Package org.apache.maven.shared.utils.io

Class IOUtil

  • public final class IOUtil
extends java.lang.Object
    General IO Stream manipulation.

    This class provides static utility methods for input/output operations, particularly buffered copying between sources (InputStream, Reader, String and byte[]) and destinations (OutputStream, Writer, String and byte[]).

    Unless otherwise noted, these copy methods do not flush or close the streams. Often, doing so would require making non-portable assumptions about the streams' origin and further use. This means that both streams' close() methods must be called after copying. if one omits this step, then the stream resources (sockets, file descriptors) are released when the associated Stream is garbage-collected. It is not a good idea to rely on this mechanism. For a good overview of the distinction between "memory management" and "resource management", see this UnixReview article

    For each copy method, a variant is provided that allows the caller to specify the buffer size (the default is 4k). As the buffer size can have a fairly large impact on speed, this may be worth tweaking. Often "large buffer -> faster" does not hold, even for large data transfers.

    For byte-to-char methods, a copy variant allows the encoding to be selected (otherwise the platform default is used).

    The copy methods use an internal buffer when copying. It is therefore advisable not to deliberately wrap the stream arguments to the copy methods in Buffered* streams. For example, don't do the following:

    copy( new BufferedInputStream( in ), new BufferedOutputStream( out ) );

    The rationale is as follows:

    Imagine that an InputStream's read() is a very expensive operation, which would usually suggest wrapping in a BufferedInputStream. The BufferedInputStream works by issuing infrequent InputStream.read(byte[] b, int off, int len) requests on the underlying InputStream, to fill an internal buffer, from which further read requests can inexpensively get their data (until the buffer runs out).

    However, the copy methods do the same thing, keeping an internal buffer, populated by InputStream.read(byte[] b, int off, int len) requests. Having two buffers (or three if the destination stream is also buffered) is pointless, and the unnecessary buffer management hurts performance slightly (about 3%, according to some simple experiments).

    Version:
    CVS $Revision$ $Date$
    Author:
    Peter Donald, Jeff Turner

    • Method Summary

      All Methods Static Methods Concrete Methods 
      Modifier and Type Method Description
      static void close​(java.io.InputStream inputStream)
      Closes an InputStream suppressing any IOException.
      static void close​(java.io.OutputStream outputStream)
      Closes an OutputStream suppressing any IOException.
      static void close​(java.io.Reader reader)
      Closes a Reader suppressing any IOException.
      static void close​(java.io.Writer writer)
      Closes a Writer suppressing any IOException.
      static void close​(java.nio.channels.Channel channel)
      Closes a Channel suppressing any IOException.
      static boolean contentEquals​(java.io.InputStream input1, java.io.InputStream input2)
      Compare the contents of two Streams to determine if they are equal or not.
      static void copy​(byte[] input, java.io.OutputStream output)
      Copy bytes from a byte[] to an OutputStream.
      static void copy​(byte[] input, java.io.Writer output)
      Copy and convert bytes from a byte[] to chars on a Writer.
      static void copy​(byte[] input, java.io.Writer output, int bufferSize)
      Copy and convert bytes from a byte[] to chars on a Writer.
      static void copy​(byte[] input, java.io.Writer output, java.lang.String encoding)
      Copy and convert bytes from a byte[] to chars on a Writer, using the specified encoding.
      static void copy​(byte[] input, java.io.Writer output, java.lang.String encoding, int bufferSize)
      Copy and convert bytes from a byte[] to chars on a Writer, using the specified encoding.
      static void copy​(java.io.InputStream input, java.io.OutputStream output)
      Copy bytes from an InputStream to an OutputStream.
      static void copy​(java.io.InputStream input, java.io.OutputStream output, int bufferSize)
      Copy bytes from an InputStream to an OutputStream.
      static void copy​(java.io.InputStream input, java.io.Writer output)
      Copy and convert bytes from an InputStream to chars on a Writer.
      static void copy​(java.io.InputStream input, java.io.Writer output, int bufferSize)
      Copy and convert bytes from an InputStream to chars on a Writer.
      static void copy​(java.io.InputStream input, java.io.Writer output, java.lang.String encoding)
      Copy and convert bytes from an InputStream to chars on a Writer, using the specified encoding.
      static void copy​(java.io.InputStream input, java.io.Writer output, java.lang.String encoding, int bufferSize)
      Copy and convert bytes from an InputStream to chars on a Writer, using the specified encoding.
      static void copy​(java.io.Reader input, java.io.OutputStream output)
      Serialize chars from a Reader to bytes on an OutputStream, and flush the OutputStream.
      static void copy​(java.io.Reader input, java.io.OutputStream output, int bufferSize)
      Serialize chars from a Reader to bytes on an OutputStream, and flush the OutputStream.
      static void copy​(java.io.Reader input, java.io.Writer output)
      Copy chars from a Reader to a Writer.
      static void copy​(java.io.Reader input, java.io.Writer output, int bufferSize)
      Copy chars from a Reader to a Writer.
      static void copy​(java.lang.String input, java.io.OutputStream output)
      Serialize chars from a String to bytes on an OutputStream, and flush the OutputStream.
      static void copy​(java.lang.String input, java.io.OutputStream output, int bufferSize)
      Serialize chars from a String to bytes on an OutputStream, and flush the OutputStream.
      static void copy​(java.lang.String input, java.io.Writer output)
      Copy chars from a String to a Writer.
      static byte[] toByteArray​(java.io.InputStream input)
      Get the contents of an InputStream as a byte[].
      static byte[] toByteArray​(java.io.InputStream input, int bufferSize)
      Get the contents of an InputStream as a byte[].
      static byte[] toByteArray​(java.io.Reader input)
      Get the contents of a Reader as a byte[].
      static byte[] toByteArray​(java.io.Reader input, int bufferSize)
      Get the contents of a Reader as a byte[].
      static byte[] toByteArray​(java.lang.String input)
      Get the contents of a String as a byte[].
      static byte[] toByteArray​(java.lang.String input, int bufferSize)
      Get the contents of a String as a byte[].
      static java.lang.String toString​(byte[] input)
      Get the contents of a byte[] as a String.
      static java.lang.String toString​(byte[] input, int bufferSize)
      Get the contents of a byte[] as a String.
      static java.lang.String toString​(byte[] input, java.lang.String encoding)
      Get the contents of a byte[] as a String.
      static java.lang.String toString​(byte[] input, java.lang.String encoding, int bufferSize)
      Get the contents of a byte[] as a String.
      static java.lang.String toString​(java.io.InputStream input)
      Get the contents of an InputStream as a String.
      static java.lang.String toString​(java.io.InputStream input, int bufferSize)
      Get the contents of an InputStream as a String.
      static java.lang.String toString​(java.io.InputStream input, java.lang.String encoding)
      Get the contents of an InputStream as a String.
      static java.lang.String toString​(java.io.InputStream input, java.lang.String encoding, int bufferSize)
      Get the contents of an InputStream as a String.
      static java.lang.String toString​(java.io.Reader input)
      Get the contents of a Reader as a String.
      static java.lang.String toString​(java.io.Reader input, int bufferSize)
      Get the contents of a Reader as a String.

      • Methods inherited from class java.lang.Object

        clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

    • Method Detail

      • copy

        public static void copy​(@Nonnull
                        java.io.InputStream input,
                        @Nonnull
                        java.io.OutputStream output)
                 throws java.io.IOException
        Copy bytes from an InputStream to an OutputStream.
        Parameters:
        input - The input size.
        output - The resulting output.
        Throws:
        java.io.IOException - in case of an error.

      • copy

        public static void copy​(@Nonnull
                        java.io.InputStream input,
                        @Nonnull
                        java.io.OutputStream output,
                        int bufferSize)
                 throws java.io.IOException
        Copy bytes from an InputStream to an OutputStream.
        Parameters:
        input - The input size.
        output - The resulting output.
        bufferSize - Size of internal buffer to use.
        Throws:
        java.io.IOException - in case of an error.

      • copy

        public static void copy​(@Nonnull
                        java.io.Reader input,
                        @Nonnull
                        java.io.Writer output)
                 throws java.io.IOException
        Copy chars from a Reader to a Writer.
        Parameters:
        input - The input size.
        output - The resulting output.
        Throws:
        java.io.IOException - in case of failure.

      • copy

        public static void copy​(@Nonnull
                        java.io.Reader input,
                        @Nonnull
                        java.io.Writer output,
                        int bufferSize)
                 throws java.io.IOException
        Copy chars from a Reader to a Writer.
        Parameters:
        input - The input size.
        output - The resulting output.
        bufferSize - Size of internal buffer to use.
        Throws:
        java.io.IOException - in case of failure.

      • copy

        public static void copy​(@Nonnull
                        java.io.InputStream input,
                        @Nonnull
                        java.io.Writer output)
                 throws java.io.IOException
        Copy and convert bytes from an InputStream to chars on a Writer. The platform's default encoding is used for the byte-to-char conversion.
        Parameters:
        input - The input size.
        output - The resulting output.
        Throws:
        java.io.IOException - in case of failure.

      • copy

        public static void copy​(@Nonnull
                        java.io.InputStream input,
                        @Nonnull
                        java.io.Writer output,
                        int bufferSize)
                 throws java.io.IOException
        Copy and convert bytes from an InputStream to chars on a Writer. The platform's default encoding is used for the byte-to-char conversion.
        Parameters:
        input - The input size.
        output - The resulting output.
        bufferSize - Size of internal buffer to use.
        Throws:
        java.io.IOException - in case of failure.

      • copy

        public static void copy​(@Nonnull
                        java.io.InputStream input,
                        @Nonnull
                        java.io.Writer output,
                        @Nonnull
                        java.lang.String encoding)
                 throws java.io.IOException
        Copy and convert bytes from an InputStream to chars on a Writer, using the specified encoding.
        Parameters:
        input - The input size.
        output - The resulting output.
        encoding - The name of a supported character encoding. See the IANA Charset Registry for a list of valid encoding types.
        Throws:
        java.io.IOException - in case of failure.

      • copy

        public static void copy​(@Nonnull
                        java.io.InputStream input,
                        @Nonnull
                        java.io.Writer output,
                        @Nonnull
                        java.lang.String encoding,
                        int bufferSize)
                 throws java.io.IOException
        Copy and convert bytes from an InputStream to chars on a Writer, using the specified encoding.
        Parameters:
        encoding - The name of a supported character encoding. See the IANA Charset Registry for a list of valid encoding types.
        input - The input size.
        output - The resulting output.
        bufferSize - Size of internal buffer to use.
        Throws:
        java.io.IOException - in case of failure.

      • toString

        @Nonnull
public static java.lang.String toString​(@Nonnull
                                        java.io.InputStream input)
                                 throws java.io.IOException
        Get the contents of an InputStream as a String. The platform's default encoding is used for the byte-to-char conversion.
        Parameters:
        input - The input size.
        Returns:
        The resulting string.
        Throws:
        java.io.IOException - in case of failure.

      • toString

        @Nonnull
public static java.lang.String toString​(@Nonnull
                                        java.io.InputStream input,
                                        int bufferSize)
                                 throws java.io.IOException
        Get the contents of an InputStream as a String. The platform's default encoding is used for the byte-to-char conversion.
        Parameters:
        input - The input size.
        bufferSize - Size of internal buffer to use.
        Returns:
        the resulting string.
        Throws:
        java.io.IOException - in case of failure.

      • toString

        @Nonnull
public static java.lang.String toString​(@Nonnull
                                        java.io.InputStream input,
                                        @Nonnull
                                        java.lang.String encoding)
                                 throws java.io.IOException
        Get the contents of an InputStream as a String.
        Parameters:
        input - The input size.
        encoding - The name of a supported character encoding. See the IANA Charset Registry for a list of valid encoding types.
        Returns:
        the converted string.
        Throws:
        java.io.IOException - in case of failure.

      • toString

        @Nonnull
public static java.lang.String toString​(@Nonnull
                                        java.io.InputStream input,
                                        @Nonnull
                                        java.lang.String encoding,
                                        int bufferSize)
                                 throws java.io.IOException
        Get the contents of an InputStream as a String.
        Parameters:
        input - The input size.
        encoding - The name of a supported character encoding. See the IANA Charset Registry for a list of valid encoding types.
        bufferSize - Size of internal buffer to use.
        Returns:
        The converted string.
        Throws:
        java.io.IOException - in case of failure.

      • toByteArray

        @Nonnull
public static byte[] toByteArray​(@Nonnull
                                 java.io.InputStream input)
                          throws java.io.IOException
        Get the contents of an InputStream as a byte[].
        Parameters:
        input - The input size.
        Returns:
        the resulting byte array.
        Throws:
        java.io.IOException - in case of failure.

      • toByteArray

        @Nonnull
public static byte[] toByteArray​(@Nonnull
                                 java.io.InputStream input,
                                 int bufferSize)
                          throws java.io.IOException
        Get the contents of an InputStream as a byte[].
        Parameters:
        input - The input size.
        bufferSize - Size of internal buffer to use.
        Returns:
        the resulting byte array.
        Throws:
        java.io.IOException - in case of failure.

      • copy

        public static void copy​(@Nonnull
                        java.io.Reader input,
                        @Nonnull
                        java.io.OutputStream output)
                 throws java.io.IOException
        Serialize chars from a Reader to bytes on an OutputStream, and flush the OutputStream.
        Parameters:
        input - The input size.
        output - The resulting output.
        Throws:
        java.io.IOException - in case of failure.

      • copy

        public static void copy​(@Nonnull
                        java.io.Reader input,
                        @Nonnull
                        java.io.OutputStream output,
                        int bufferSize)
                 throws java.io.IOException
        Serialize chars from a Reader to bytes on an OutputStream, and flush the OutputStream.
        Parameters:
        input - The input size.
        output - The resulting output.
        bufferSize - Size of internal buffer to use.
        Throws:
        java.io.IOException - in case of failure.

      • toString

        @Nonnull
public static java.lang.String toString​(@Nonnull
                                        java.io.Reader input)
                                 throws java.io.IOException
        Get the contents of a Reader as a String.
        Parameters:
        input - The input size.
        Returns:
        The converted string.
        Throws:
        java.io.IOException - in case of failure.

      • toString

        @Nonnull
public static java.lang.String toString​(@Nonnull
                                        java.io.Reader input,
                                        int bufferSize)
                                 throws java.io.IOException
        Get the contents of a Reader as a String.
        Parameters:
        input - The input size.
        bufferSize - Size of internal buffer to use.
        Returns:
        the resulting byte array.
        Throws:
        java.io.IOException - in case of failure.

      • toByteArray

        @Nonnull
public static byte[] toByteArray​(@Nonnull
                                 java.io.Reader input)
                          throws java.io.IOException
        Get the contents of a Reader as a byte[].
        Parameters:
        input - The input size.
        Returns:
        the resulting byte array.
        Throws:
        java.io.IOException - in case of failure.

      • toByteArray

        @Nonnull
public static byte[] toByteArray​(@Nonnull
                                 java.io.Reader input,
                                 int bufferSize)
                          throws java.io.IOException
        Get the contents of a Reader as a byte[].
        Parameters:
        input - The input size.
        bufferSize - Size of internal buffer to use.
        Returns:
        the resulting byte array.
        Throws:
        java.io.IOException - in case of failure.

      • copy

        public static void copy​(@Nonnull
                        java.lang.String input,
                        @Nonnull
                        java.io.OutputStream output)
                 throws java.io.IOException
        Serialize chars from a String to bytes on an OutputStream, and flush the OutputStream.
        Parameters:
        input - The input size.
        output - The resulting output.
        Throws:
        java.io.IOException - in case of failure.

      • copy

        public static void copy​(@Nonnull
                        java.lang.String input,
                        @Nonnull
                        java.io.OutputStream output,
                        int bufferSize)
                 throws java.io.IOException
        Serialize chars from a String to bytes on an OutputStream, and flush the OutputStream.
        Parameters:
        input - The input size.
        output - The resulting output.
        bufferSize - Size of internal buffer to use.
        Throws:
        java.io.IOException - in case of failure.

      • copy

        public static void copy​(@Nonnull
                        java.lang.String input,
                        @Nonnull
                        java.io.Writer output)
                 throws java.io.IOException
        Copy chars from a String to a Writer.
        Parameters:
        input - Input string.
        output - resulting output Writer
        Throws:
        java.io.IOException - in case of failure.

      • toByteArray

        @Nonnull
public static byte[] toByteArray​(@Nonnull
                                 java.lang.String input)
                          throws java.io.IOException
        Get the contents of a String as a byte[].
        Parameters:
        input - The input size.
        Returns:
        The resulting byte array.
        Throws:
        java.io.IOException - in case of failure.

      • toByteArray

        @Nonnull
public static byte[] toByteArray​(@Nonnull
                                 java.lang.String input,
                                 int bufferSize)
                          throws java.io.IOException
        Get the contents of a String as a byte[].
        Parameters:
        input - The input size.
        bufferSize - Size of internal buffer to use.
        Returns:
        The resulting byte array.
        Throws:
        java.io.IOException - in case of failure.

      • copy

        public static void copy​(@Nonnull
                        byte[] input,
                        @Nonnull
                        java.io.Writer output)
                 throws java.io.IOException
        Copy and convert bytes from a byte[] to chars on a Writer. The platform's default encoding is used for the byte-to-char conversion.
        Parameters:
        input - The input size.
        output - The resulting output.
        Throws:
        java.io.IOException - in case of failure.

      • copy

        public static void copy​(@Nonnull
                        byte[] input,
                        @Nonnull
                        java.io.Writer output,
                        int bufferSize)
                 throws java.io.IOException
        Copy and convert bytes from a byte[] to chars on a Writer. The platform's default encoding is used for the byte-to-char conversion.
        Parameters:
        input - The input size.
        output - The resulting output.
        bufferSize - Size of internal buffer to use.
        Throws:
        java.io.IOException - in case of failure.

      • copy

        public static void copy​(@Nonnull
                        byte[] input,
                        @Nonnull
                        java.io.Writer output,
                        java.lang.String encoding)
                 throws java.io.IOException
        Copy and convert bytes from a byte[] to chars on a Writer, using the specified encoding.
        Parameters:
        encoding - The name of a supported character encoding. See the IANA Charset Registry for a list of valid encoding types.
        input - The input size.
        output - The resulting output.
        Throws:
        java.io.IOException - in case of failure.

      • copy

        public static void copy​(@Nonnull
                        byte[] input,
                        @Nonnull
                        java.io.Writer output,
                        @Nonnull
                        java.lang.String encoding,
                        int bufferSize)
                 throws java.io.IOException
        Copy and convert bytes from a byte[] to chars on a Writer, using the specified encoding.
        Parameters:
        encoding - The name of a supported character encoding. See the IANA Charset Registry for a list of valid encoding types.
        input - The input bytes.
        output - The output buffer Writer
        bufferSize - Size of internal buffer to use.
        Throws:
        java.io.IOException - in case of failure.

      • toString

        @Nonnull
public static java.lang.String toString​(@Nonnull
                                        byte[] input)
                                 throws java.io.IOException
        Get the contents of a byte[] as a String. The platform's default encoding is used for the byte-to-char conversion.
        Parameters:
        input - The input bytes.
        Returns:
        The resulting string.
        Throws:
        java.io.IOException - in case of failure.

      • toString

        @Nonnull
public static java.lang.String toString​(@Nonnull
                                        byte[] input,
                                        int bufferSize)
                                 throws java.io.IOException
        Get the contents of a byte[] as a String. The platform's default encoding is used for the byte-to-char conversion.
        Parameters:
        bufferSize - Size of internal buffer to use.
        input - The input bytes.
        Returns:
        The created string.
        Throws:
        java.io.IOException - in case of failure.

      • toString

        @Nonnull
public static java.lang.String toString​(@Nonnull
                                        byte[] input,
                                        @Nonnull
                                        java.lang.String encoding)
                                 throws java.io.IOException
        Get the contents of a byte[] as a String.
        Parameters:
        encoding - The name of a supported character encoding. See the IANA Charset Registry for a list of valid encoding types.
        input - The input bytes.
        Returns:
        The resulting string.
        Throws:
        java.io.IOException - in case of failure.

      • toString

        @Nonnull
public static java.lang.String toString​(@Nonnull
                                        byte[] input,
                                        @Nonnull
                                        java.lang.String encoding,
                                        int bufferSize)
                                 throws java.io.IOException
        Get the contents of a byte[] as a String.
        Parameters:
        encoding - The name of a supported character encoding. See the IANA Charset Registry for a list of valid encoding types.
        bufferSize - Size of internal buffer to use.
        input - Input bytes.
        Returns:
        The resulting string.
        Throws:
        java.io.IOException - in case of failure.

      • copy

        public static void copy​(@Nonnull
                        byte[] input,
                        @Nonnull
                        java.io.OutputStream output)
                 throws java.io.IOException
        Copy bytes from a byte[] to an OutputStream.
        Parameters:
        input - Input byte array.
        output - output stream OutputStream
        Throws:
        java.io.IOException - in case of failure.

      • contentEquals

        public static boolean contentEquals​(@Nonnull
                                    java.io.InputStream input1,
                                    @Nonnull
                                    java.io.InputStream input2)
                             throws java.io.IOException
        Compare the contents of two Streams to determine if they are equal or not.
        Parameters:
        input1 - the first stream
        input2 - the second stream
        Returns:
        true if the content of the streams are equal or they both don't exist, false otherwise
        Throws:
        java.io.IOException - in case of failure.

      • close

        public static void close​(@Nullable
                         java.nio.channels.Channel channel)
        Closes a Channel suppressing any IOException.

        Note:
        The usecase justifying this method is a shortcoming of the Java language up to but not including Java 7. For any code targetting Java 7 or later use of this method is highly discouraged and the try-with-resources statement should be used instead. Care must be taken to not use this method in a way IOExceptions get suppressed incorrectly. You must close all resources in use inside the try block to not suppress exceptions in the finally block incorrectly by using this method.

        Example:

         // Introduce variables for the resources and initialize them to null. This cannot throw an exception.
 Closeable resource1 = null;
 Closeable resource2 = null;
 try
 {
     // Obtain a resource object and assign it to variable resource1. This may throw an exception.
     // If successful, resource1 != null.
     resource1 = ...

     // Obtain a resource object and assign it to variable resource2. This may throw an exception.
     // If successful, resource2 != null. Not reached if an exception has been thrown above.
     resource2 = ...

     // Perform operations on the resources. This may throw an exception. Not reached if an exception has been
     // thrown above. Note: Treat the variables resource1 and resource2 the same way as if they would have been
     // declared with the final modifier - that is - do NOT write anyting like resource1 = something else or
     // resource2 = something else here.
     resource1 ...
     resource2 ...

     // Finally, close the resources and set the variables to null indicating successful completion.
     // This may throw an exception. Not reached if an exception has been thrown above.
     resource1.close();
     resource1 = null;
     // Not reached if an exception has been thrown above.
     resource2.close();
     resource2 = null;

     // All resources are closed at this point and all operations (up to here) completed successfully without
     // throwing an exception we would need to handle (by letting it propagate or by catching and handling it).
 }
 finally
 {
     // Cleanup any resource not closed in the try block due to an exception having been thrown and suppress any
     // exception this may produce to not stop the exception from the try block to be propagated. If the try
     // block completed successfully, all variables will have been set to null there and this will not do
     // anything. This is just to cleanup properly in case of an exception.

     IOUtil.close( resource1 );
     IOUtil.close( resource2 );

     // Without that utility method you would need to write the following:
     //
     // try
     // {
     //     if ( resource1 != null )
     //     {
     //         resource1.close();
     //     }
     // }
     // catch( IOException e )
     // {
     //     Suppressed. If resource1 != null, an exception has already been thrown in the try block we need to
     //     propagate instead of this one.
     // }
     // finally
     // {
     //     try
     //     {
     //         if ( resource2 != null )
     //         {
     //             resource2.close();
     //         }
     //     }
     //     catch ( IOException e )
     //     {
     //         Suppressed. If resource2 != null, an exception has already been thrown in the try block we need to
     //         propagate instead of this one.
     //     }
     // }
 }

        Parameters:
        channel - The channel to close or null.

      • close

        public static void close​(@Nullable
                         java.io.InputStream inputStream)
        Closes an InputStream suppressing any IOException.

        Note:
        The usecase justifying this method is a shortcoming of the Java language up to but not including Java 7. For any code targeting Java 7 or later use of this method is highly discouraged and the try-with-resources statement should be used instead. Care must be taken to not use this method in a way IOExceptions get suppressed incorrectly. You must close all resources in use inside the try block to not suppress exceptions in the finally block incorrectly by using this method.

        Example:

         // Introduce variables for the resources and initialize them to null. This cannot throw an exception.
 Closeable resource1 = null;
 Closeable resource2 = null;
 try
 {
     // Obtain a resource object and assign it to variable resource1. This may throw an exception.
     // If successful, resource1 != null.
     resource1 = ...

     // Obtain a resource object and assign it to variable resource2. This may throw an exception.
     // If successful, resource2 != null. Not reached if an exception has been thrown above.
     resource2 = ...

     // Perform operations on the resources. This may throw an exception. Not reached if an exception has been
     // thrown above. Note: Treat the variables resource1 and resource2 the same way as if they would have been
     // declared with the final modifier - that is - do NOT write anyting like resource1 = something else or
     // resource2 = something else here.
     resource1 ...
     resource2 ...

     // Finally, close the resources and set the variables to null indicating successful completion.
     // This may throw an exception. Not reached if an exception has been thrown above.
     resource1.close();
     resource1 = null;
     // This may throw an exception. Not reached if an exception has been thrown above.
     resource2.close();
     resource2 = null;

     // All resources are closed at this point and all operations (up to here) completed successfully without
     // throwing an exception we would need to handle (by letting it propagate or by catching and handling it).
 }
 finally
 {
     // Cleanup any resource not closed in the try block due to an exception having been thrown and suppress any
     // exception this may produce to not stop the exception from the try block to be propagated. If the try
     // block completed successfully, all variables will have been set to null there and this will not do
     // anything. This is just to cleanup properly in case of an exception.

     IOUtil.close( resource1 );
     IOUtil.close( resource2 );

     // Without that utility method you would need to write the following:
     //
     // try
     // {
     //     if ( resource1 != null )
     //     {
     //         resource1.close();
     //     }
     // }
     // catch( IOException e )
     // {
     //     Suppressed. If resource1 != null, an exception has already been thrown in the try block we need to
     //     propagate instead of this one.
     // }
     // finally
     // {
     //     try
     //     {
     //         if ( resource2 != null )
     //         {
     //             resource2.close();
     //         }
     //     }
     //     catch ( IOException e )
     //     {
     //         Suppressed. If resource2 != null, an exception has already been thrown in the try block we need to
     //         propagate instead of this one.
     //     }
     // }
 }

        Parameters:
        inputStream - The stream to close or null.

      • close

        public static void close​(@Nullable
                         java.io.OutputStream outputStream)
        Closes an OutputStream suppressing any IOException.

        Note:
        The usecase justifying this method is a shortcoming of the Java language up to but not including Java 7. For any code targeting Java 7 or later use of this method is highly discouraged and the try-with-resources statement should be used instead. Care must be taken to not use this method in a way IOExceptions get suppressed incorrectly. You must close all resources in use inside the try block to not suppress exceptions in the finally block incorrectly by using this method.

        Example:

         // Introduce variables for the resources and initialize them to null. This cannot throw an exception.
 Closeable resource1 = null;
 Closeable resource2 = null;
 try
 {
     // Obtain a resource object and assign it to variable resource1. This may throw an exception.
     // If successful, resource1 != null.
     resource1 = ...

     // Obtain a resource object and assign it to variable resource2. This may throw an exception.
     // If successful, resource2 != null. Not reached if an exception has been thrown above.
     resource2 = ...

     // Perform operations on the resources. This may throw an exception. Not reached if an exception has been
     // thrown above. Note: Treat the variables resource1 and resource2 the same way as if they would have been
     // declared with the final modifier - that is - do NOT write anyting like resource1 = something else or
     // resource2 = something else here.
     resource1 ...
     resource2 ...

     // Finally, close the resources and set the variables to null indicating successful completion.
     // This may throw an exception. Not reached if an exception has been thrown above.
     resource1.close();
     resource1 = null;
     // This may throw an exception. Not reached if an exception has been thrown above.
     resource2.close();
     resource2 = null;

     // All resources are closed at this point and all operations (up to here) completed successfully without
     // throwing an exception we would need to handle (by letting it propagate or by catching and handling it).
 }
 finally
 {
     // Cleanup any resource not closed in the try block due to an exception having been thrown and suppress any
     // exception this may produce to not stop the exception from the try block to be propagated. If the try
     // block completed successfully, all variables will have been set to null there and this will not do
     // anything. This is just to cleanup properly in case of an exception.

     IOUtil.close( resource1 );
     IOUtil.close( resource2 );

     // Without that utility method you would need to write the following:
     //
     // try
     // {
     //     if ( resource1 != null )
     //     {
     //         resource1.close();
     //     }
     // }
     // catch( IOException e )
     // {
     //     Suppressed. If resource1 != null, an exception has already been thrown in the try block we need to
     //     propagate instead of this one.
     // }
     // finally
     // {
     //     try
     //     {
     //         if ( resource2 != null )
     //         {
     //             resource2.close();
     //         }
     //     }
     //     catch ( IOException e )
     //     {
     //         Suppressed. If resource2 != null, an exception has already been thrown in the try block we need to
     //         propagate instead of this one.
     //     }
     // }
 }

        Parameters:
        outputStream - The stream to close or null.

      • close

        public static void close​(@Nullable
                         java.io.Reader reader)
        Closes a Reader suppressing any IOException.

        Note:
        The usecase justifying this method is a shortcoming of the Java language up to but not including Java 7. For any code targeting Java 7 or later use of this method is highly discouraged and the try-with-resources statement should be used instead. Care must be taken to not use this method in a way IOExceptions get suppressed incorrectly. You must close all resources in use inside the try block to not suppress exceptions in the finally block incorrectly by using this method.

        Example:

         // Introduce variables for the resources and initialize them to null. This cannot throw an exception.
 Closeable resource1 = null;
 Closeable resource2 = null;
 try
 {
     // Obtain a resource object and assign it to variable resource1. This may throw an exception.
     // If successful, resource1 != null.
     resource1 = ...

     // Obtain a resource object and assign it to variable resource2. This may throw an exception.
     // If successful, resource2 != null. Not reached if an exception has been thrown above.
     resource2 = ...

     // Perform operations on the resources. This may throw an exception. Not reached if an exception has been
     // thrown above. Note: Treat the variables resource1 and resource2 the same way as if they would have been
     // declared with the final modifier - that is - do NOT write anyting like resource1 = something else or
     // resource2 = something else here.
     resource1 ...
     resource2 ...

     // Finally, close the resources and set the variables to null indicating successful completion.
     // This may throw an exception. Not reached if an exception has been thrown above.
     resource1.close();
     resource1 = null;
     // This may throw an exception. Not reached if an exception has been thrown above.
     resource2.close();
     resource2 = null;

     // All resources are closed at this point and all operations (up to here) completed successfully without
     // throwing an exception we would need to handle (by letting it propagate or by catching and handling it).
 }
 finally
 {
     // Cleanup any resource not closed in the try block due to an exception having been thrown and suppress any
     // exception this may produce to not stop the exception from the try block to be propagated. If the try
     // block completed successfully, all variables will have been set to null there and this will not do
     // anything. This is just to cleanup properly in case of an exception.

     IOUtil.close( resource1 );
     IOUtil.close( resource2 );

     // Without that utility method you would need to write the following:
     //
     // try
     // {
     //     if ( resource1 != null )
     //     {
     //         resource1.close();
     //     }
     // }
     // catch( IOException e )
     // {
     //     Suppressed. If resource1 != null, an exception has already been thrown in the try block we need to
     //     propagate instead of this one.
     // }
     // finally
     // {
     //     try
     //     {
     //         if ( resource2 != null )
     //         {
     //             resource2.close();
     //         }
     //     }
     //     catch ( IOException e )
     //     {
     //         Suppressed. If resource2 != null, an exception has already been thrown in the try block we need to
     //         propagate instead of this one.
     //     }
     // }
 }

        Parameters:
        reader - The reader to close or null.

      • close

        public static void close​(@Nullable
                         java.io.Writer writer)
        Closes a Writer suppressing any IOException.

        Note:
        The usecase justifying this method is a shortcoming of the Java language up to but not including Java 7. For any code targeting Java 7 or later use of this method is highly discouraged and the try-with-resources statement should be used instead. Care must be taken to not use this method in a way IOExceptions get suppressed incorrectly. You must close all resources in use inside the try block to not suppress exceptions in the finally block incorrectly by using this method.

        Example:

         // Introduce variables for the resources and initialize them to null. This cannot throw an exception.
 Closeable resource1 = null;
 Closeable resource2 = null;
 try
 {
     // Obtain a resource object and assign it to variable resource1. This may throw an exception.
     // If successful, resource1 != null.
     resource1 = ...

     // Obtain a resource object and assign it to variable resource2. This may throw an exception.
     // If successful, resource2 != null. Not reached if an exception has been thrown above.
     resource2 = ...

     // Perform operations on the resources. This may throw an exception. Not reached if an exception has been
     // thrown above. Note: Treat the variables resource1 and resource2 the same way as if they would have been
     // declared with the final modifier - that is - do NOT write anyting like resource1 = something else or
     // resource2 = something else here.
     resource1 ...
     resource2 ...

     // Finally, close the resources and set the variables to null indicating successful completion.
     // This may throw an exception. Not reached if an exception has been thrown above.
     resource1.close();
     resource1 = null;
     // This may throw an exception. Not reached if an exception has been thrown above.
     resource2.close();
     resource2 = null;

     // All resources are closed at this point and all operations (up to here) completed successfully without
     // throwing an exception we would need to handle (by letting it propagate or by catching and handling it).
 }
 finally
 {
     // Cleanup any resource not closed in the try block due to an exception having been thrown and suppress any
     // exception this may produce to not stop the exception from the try block to be propagated. If the try
     // block completed successfully, all variables will have been set to null there and this will not do
     // anything. This is just to cleanup properly in case of an exception.

     IOUtil.close( resource1 );
     IOUtil.close( resource2 );

     // Without that utility method you would need to write the following:
     //
     // try
     // {
     //     if ( resource1 != null )
     //     {
     //         resource1.close();
     //     }
     // }
     // catch( IOException e )
     // {
     //     Suppressed. If resource1 != null, an exception has already been thrown in the try block we need to
     //     propagate instead of this one.
     // }
     // finally
     // {
     //     try
     //     {
     //         if ( resource2 != null )
     //         {
     //             resource2.close();
     //         }
     //     }
     //     catch ( IOException e )
     //     {
     //         Suppressed. If resource2 != null, an exception has already been thrown in the try block we need to
     //         propagate instead of this one.
     //     }
     // }
 }

        Parameters:
        writer - The writer to close or null.