public final class IOUtil extends Object
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).
| Modifier and Type | Method and Description |
|---|---|
static void |
close(Channel channel)
Closes a
Channel suppressing any IOException. |
static void |
close(InputStream inputStream)
Closes an
InputStream suppressing any IOException. |
static void |
close(OutputStream outputStream)
Closes an
OutputStream suppressing any IOException. |
static void |
close(Reader reader)
Closes a
Reader suppressing any IOException. |
static void |
close(Writer writer)
Closes a
Writer suppressing any IOException. |
static boolean |
contentEquals(InputStream input1,
InputStream input2)
Compare the contents of two Streams to determine if they are equal or not.
|
static void |
copy(byte[] input,
OutputStream output)
Copy bytes from a
byte[] to an OutputStream. |
static void |
copy(byte[] input,
Writer output)
Copy and convert bytes from a
byte[] to chars on a
Writer. |
static void |
copy(byte[] input,
Writer output,
int bufferSize)
Copy and convert bytes from a
byte[] to chars on a
Writer. |
static void |
copy(byte[] input,
Writer output,
String encoding)
Copy and convert bytes from a
byte[] to chars on a
Writer, using the specified encoding. |
static void |
copy(byte[] input,
Writer output,
String encoding,
int bufferSize)
Copy and convert bytes from a
byte[] to chars on a
Writer, using the specified encoding. |
static void |
copy(InputStream input,
OutputStream output)
Copy bytes from an
InputStream to an OutputStream. |
static void |
copy(InputStream input,
OutputStream output,
int bufferSize)
Copy bytes from an
InputStream to an OutputStream. |
static void |
copy(InputStream input,
Writer output)
Copy and convert bytes from an
InputStream to chars on a
Writer. |
static void |
copy(InputStream input,
Writer output,
int bufferSize)
Copy and convert bytes from an
InputStream to chars on a
Writer. |
static void |
copy(InputStream input,
Writer output,
String encoding)
Copy and convert bytes from an
InputStream to chars on a
Writer, using the specified encoding. |
static void |
copy(InputStream input,
Writer output,
String encoding,
int bufferSize)
Copy and convert bytes from an
InputStream to chars on a
Writer, using the specified encoding. |
static void |
copy(Reader input,
OutputStream output)
Serialize chars from a
Reader to bytes on an OutputStream, and
flush the OutputStream. |
static void |
copy(Reader input,
OutputStream output,
int bufferSize)
Serialize chars from a
Reader to bytes on an OutputStream, and
flush the OutputStream. |
static void |
copy(Reader input,
Writer output)
Copy chars from a
Reader to a Writer. |
static void |
copy(Reader input,
Writer output,
int bufferSize)
Copy chars from a
Reader to a Writer. |
static void |
copy(String input,
OutputStream output)
Serialize chars from a
String to bytes on an OutputStream, and
flush the OutputStream. |
static void |
copy(String input,
OutputStream output,
int bufferSize)
Serialize chars from a
String to bytes on an OutputStream, and
flush the OutputStream. |
static void |
copy(String input,
Writer output)
Copy chars from a
String to a Writer. |
static byte[] |
toByteArray(InputStream input)
Get the contents of an
InputStream as a byte[]. |
static byte[] |
toByteArray(InputStream input,
int bufferSize)
Get the contents of an
InputStream as a byte[]. |
static byte[] |
toByteArray(Reader input)
Get the contents of a
Reader as a byte[]. |
static byte[] |
toByteArray(Reader input,
int bufferSize)
Get the contents of a
Reader as a byte[]. |
static byte[] |
toByteArray(String input)
Get the contents of a
String as a byte[]. |
static byte[] |
toByteArray(String input,
int bufferSize)
Get the contents of a
String as a byte[]. |
static String |
toString(byte[] input)
Get the contents of a
byte[] as a String. |
static String |
toString(byte[] input,
int bufferSize)
Get the contents of a
byte[] as a String. |
static String |
toString(byte[] input,
String encoding)
Get the contents of a
byte[] as a String. |
static String |
toString(byte[] input,
String encoding,
int bufferSize)
Get the contents of a
byte[] as a String. |
static String |
toString(InputStream input)
Get the contents of an
InputStream as a String. |
static String |
toString(InputStream input,
int bufferSize)
Get the contents of an
InputStream as a String. |
static String |
toString(InputStream input,
String encoding)
Get the contents of an
InputStream as a String. |
static String |
toString(InputStream input,
String encoding,
int bufferSize)
Get the contents of an
InputStream as a String. |
static String |
toString(Reader input)
Get the contents of a
Reader as a String. |
static String |
toString(Reader input,
int bufferSize)
Get the contents of a
Reader as a String. |
public static void copy(@Nonnull InputStream input, @Nonnull OutputStream output) throws IOException
InputStream to an OutputStream.input - The input size.output - The resulting output.IOException - in case of an error.public static void copy(@Nonnull InputStream input, @Nonnull OutputStream output, int bufferSize) throws IOException
InputStream to an OutputStream.input - The input size.output - The resulting output.bufferSize - Size of internal buffer to use.IOException - in case of an error.public static void copy(@Nonnull Reader input, @Nonnull Writer output) throws IOException
Reader to a Writer.input - The input size.output - The resulting output.IOException - in case of failure.public static void copy(@Nonnull Reader input, @Nonnull Writer output, int bufferSize) throws IOException
Reader to a Writer.input - The input size.output - The resulting output.bufferSize - Size of internal buffer to use.IOException - in case of failure.public static void copy(@Nonnull InputStream input, @Nonnull Writer output) throws IOException
InputStream to chars on a
Writer.
The platform's default encoding is used for the byte-to-char conversion.input - The input size.output - The resulting output.IOException - in case of failure.public static void copy(@Nonnull InputStream input, @Nonnull Writer output, int bufferSize) throws IOException
InputStream to chars on a
Writer.
The platform's default encoding is used for the byte-to-char conversion.input - The input size.output - The resulting output.bufferSize - Size of internal buffer to use.IOException - in case of failure.public static void copy(@Nonnull InputStream input, @Nonnull Writer output, @Nonnull String encoding) throws IOException
InputStream to chars on a
Writer, using the specified encoding.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.IOException - in case of failure.public static void copy(@Nonnull InputStream input, @Nonnull Writer output, @Nonnull String encoding, int bufferSize) throws IOException
InputStream to chars on a
Writer, using the specified encoding.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.IOException - in case of failure.@Nonnull public static String toString(@Nonnull InputStream input) throws IOException
InputStream as a String.
The platform's default encoding is used for the byte-to-char conversion.input - The input size.IOException - in case of failure.@Nonnull public static String toString(@Nonnull InputStream input, int bufferSize) throws IOException
InputStream as a String.
The platform's default encoding is used for the byte-to-char conversion.input - The input size.bufferSize - Size of internal buffer to use.IOException - in case of failure.@Nonnull public static String toString(@Nonnull InputStream input, @Nonnull String encoding) throws IOException
InputStream as a String.input - The input size.encoding - The name of a supported character encoding. See the
IANA
Charset Registry for a list of valid encoding types.IOException - in case of failure.@Nonnull public static String toString(@Nonnull InputStream input, @Nonnull String encoding, int bufferSize) throws IOException
InputStream as a String.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.IOException - in case of failure.@Nonnull public static byte[] toByteArray(@Nonnull InputStream input) throws IOException
InputStream as a byte[].input - The input size.IOException - in case of failure.@Nonnull public static byte[] toByteArray(@Nonnull InputStream input, int bufferSize) throws IOException
InputStream as a byte[].input - The input size.bufferSize - Size of internal buffer to use.IOException - in case of failure.public static void copy(@Nonnull Reader input, @Nonnull OutputStream output) throws IOException
Reader to bytes on an OutputStream, and
flush the OutputStream.input - The input size.output - The resulting output.IOException - in case of failure.public static void copy(@Nonnull Reader input, @Nonnull OutputStream output, int bufferSize) throws IOException
Reader to bytes on an OutputStream, and
flush the OutputStream.input - The input size.output - The resulting output.bufferSize - Size of internal buffer to use.IOException - in case of failure.@Nonnull public static String toString(@Nonnull Reader input) throws IOException
Reader as a String.input - The input size.IOException - in case of failure.@Nonnull public static String toString(@Nonnull Reader input, int bufferSize) throws IOException
Reader as a String.input - The input size.bufferSize - Size of internal buffer to use.IOException - in case of failure.@Nonnull public static byte[] toByteArray(@Nonnull Reader input) throws IOException
Reader as a byte[].input - The input size.IOException - in case of failure.@Nonnull public static byte[] toByteArray(@Nonnull Reader input, int bufferSize) throws IOException
Reader as a byte[].input - The input size.bufferSize - Size of internal buffer to use.IOException - in case of failure.public static void copy(@Nonnull String input, @Nonnull OutputStream output) throws IOException
String to bytes on an OutputStream, and
flush the OutputStream.input - The input size.output - The resulting output.IOException - in case of failure.public static void copy(@Nonnull String input, @Nonnull OutputStream output, int bufferSize) throws IOException
String to bytes on an OutputStream, and
flush the OutputStream.input - The input size.output - The resulting output.bufferSize - Size of internal buffer to use.IOException - in case of failure.public static void copy(@Nonnull String input, @Nonnull Writer output) throws IOException
String to a Writer.input - Input string.output - resulting output WriterIOException - in case of failure.@Nonnull public static byte[] toByteArray(@Nonnull String input) throws IOException
String as a byte[].input - The input size.IOException - in case of failure.@Nonnull public static byte[] toByteArray(@Nonnull String input, int bufferSize) throws IOException
String as a byte[].input - The input size.bufferSize - Size of internal buffer to use.IOException - in case of failure.public static void copy(@Nonnull byte[] input, @Nonnull Writer output) throws IOException
byte[] to chars on a
Writer.
The platform's default encoding is used for the byte-to-char conversion.input - The input size.output - The resulting output.IOException - in case of failure.public static void copy(@Nonnull byte[] input, @Nonnull Writer output, int bufferSize) throws IOException
byte[] to chars on a
Writer.
The platform's default encoding is used for the byte-to-char conversion.input - The input size.output - The resulting output.bufferSize - Size of internal buffer to use.IOException - in case of failure.public static void copy(@Nonnull byte[] input, @Nonnull Writer output, String encoding) throws IOException
byte[] to chars on a
Writer, using the specified encoding.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.IOException - in case of failure.public static void copy(@Nonnull byte[] input, @Nonnull Writer output, @Nonnull String encoding, int bufferSize) throws IOException
byte[] to chars on a
Writer, using the specified encoding.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 WriterbufferSize - Size of internal buffer to use.IOException - in case of failure.@Nonnull public static String toString(@Nonnull byte[] input) throws IOException
byte[] as a String.
The platform's default encoding is used for the byte-to-char conversion.input - The input bytes.IOException - in case of failure.@Nonnull public static String toString(@Nonnull byte[] input, int bufferSize) throws IOException
byte[] as a String.
The platform's default encoding is used for the byte-to-char conversion.bufferSize - Size of internal buffer to use.input - The input bytes.IOException - in case of failure.@Nonnull public static String toString(@Nonnull byte[] input, @Nonnull String encoding) throws IOException
byte[] as a String.encoding - The name of a supported character encoding. See the
IANA
Charset Registry for a list of valid encoding types.input - The input bytes.IOException - in case of failure.@Nonnull public static String toString(@Nonnull byte[] input, @Nonnull String encoding, int bufferSize) throws IOException
byte[] as a String.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.IOException - in case of failure.public static void copy(@Nonnull byte[] input, @Nonnull OutputStream output) throws IOException
byte[] to an OutputStream.input - Input byte array.output - output stream OutputStreamIOException - in case of failure.public static boolean contentEquals(@Nonnull InputStream input1, @Nonnull InputStream input2) throws IOException
input1 - the first streaminput2 - the second streamIOException - in case of failure.public static void close(@Nullable Channel channel)
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.
// }
// }
}
channel - The channel to close or null.public static void close(@Nullable InputStream inputStream)
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.
// }
// }
}
inputStream - The stream to close or null.public static void close(@Nullable OutputStream outputStream)
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.
// }
// }
}
outputStream - The stream to close or null.public static void close(@Nullable Reader reader)
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.
// }
// }
}
reader - The reader to close or null.public static void close(@Nullable Writer writer)
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.
// }
// }
}
writer - The writer to close or null.Copyright © 2002–2016 The Apache Software Foundation. All rights reserved.