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 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)
Deprecated.
use try-with-resources
|
static void |
close(InputStream inputStream)
Deprecated.
use try-with-resources
|
static void |
close(OutputStream outputStream)
Deprecated.
use try-with-resources
|
static void |
close(Reader reader)
Deprecated.
use try-with-resources
|
static void |
close(Writer writer)
Deprecated.
use try-with-resources
|
static boolean |
contentEquals(InputStream input1,
InputStream input2)
Deprecated.
use
org.apache.commons.io.IOUtils.contentEquals() |
static void |
copy(byte[] input,
OutputStream output)
Deprecated.
inline this method
|
static void |
copy(byte[] input,
Writer output)
Deprecated.
always specify a character encoding
|
static void |
copy(byte[] input,
Writer output,
int bufferSize)
Deprecated.
always specify a character encoding
|
static void |
copy(byte[] input,
Writer output,
String encoding)
Deprecated.
use
org.apache.commons.io.IOUtils.write() . |
static void |
copy(byte[] input,
Writer output,
String encoding,
int bufferSize)
Deprecated.
use
org.apache.commons.io.IOUtils.write() . |
static void |
copy(InputStream input,
OutputStream output)
Deprecated.
use
org.apache.commons.io.IOUtils.copy() or in
Java 9 and later InputStream.transferTo() . |
static void |
copy(InputStream input,
OutputStream output,
int bufferSize)
Deprecated.
use
org.apache.commons.io.IOUtils.copy() or in
Java 9 and later InputStream.transferTo() . |
static void |
copy(InputStream input,
Writer output)
Deprecated.
use
org.apache.commons.io.IOUtils.copy() . |
static void |
copy(InputStream input,
Writer output,
int bufferSize)
Deprecated.
use
org.apache.commons.io.IOUtils.copy() . |
static void |
copy(InputStream input,
Writer output,
String encoding)
Deprecated.
use
org.apache.commons.io.IOUtils.copy() . |
static void |
copy(InputStream input,
Writer output,
String encoding,
int bufferSize)
Deprecated.
use
org.apache.commons.io.IOUtils.copy() . |
static void |
copy(Reader input,
OutputStream output)
Deprecated.
always specify a character encoding
|
static void |
copy(Reader input,
OutputStream output,
int bufferSize)
Deprecated.
always specify a character encoding
|
static void |
copy(Reader input,
Writer output)
Deprecated.
|
static void |
copy(Reader input,
Writer output,
int bufferSize)
Deprecated.
use
org.apache.commons.io.IOUtils.copy() . |
static void |
copy(String input,
OutputStream output)
Deprecated.
always specify a character encoding
|
static void |
copy(String input,
OutputStream output,
int bufferSize)
Deprecated.
always specify a character encoding
|
static void |
copy(String input,
Writer output)
Deprecated.
use
org.apache.commons.io.IOUtils.write() . |
static byte[] |
toByteArray(InputStream input)
Deprecated.
use
org.apache.commons.io.IOUtils.readFully() . |
static byte[] |
toByteArray(InputStream input,
int bufferSize)
Deprecated.
use
org.apache.commons.io.IOUtils.readFully() . |
static byte[] |
toByteArray(Reader input)
Deprecated.
always specify a character encoding
|
static byte[] |
toByteArray(Reader input,
int bufferSize)
Deprecated.
always specify a character encoding
|
static byte[] |
toByteArray(String input)
Deprecated.
always specify a character encoding
|
static byte[] |
toByteArray(String input,
int bufferSize)
Deprecated.
always specify a character encoding
|
static String |
toString(byte[] input)
Deprecated.
always specify a character encoding
|
static String |
toString(byte[] input,
int bufferSize)
Deprecated.
always specify a character encoding
|
static String |
toString(byte[] input,
String encoding)
Deprecated.
use
new String(input, encoding) |
static String |
toString(byte[] input,
String encoding,
int bufferSize)
Deprecated.
use
new String(input, encoding) |
static String |
toString(InputStream input)
Deprecated.
always specify a character encoding
|
static String |
toString(InputStream input,
int bufferSize)
Deprecated.
always specify a character encoding
|
static String |
toString(InputStream input,
String encoding)
Deprecated.
use
org.apache.commons.io.IOUtils.toString() . |
static String |
toString(InputStream input,
String encoding,
int bufferSize)
Deprecated.
use
org.apache.commons.io.IOUtils.toString() . |
static String |
toString(Reader input)
Deprecated.
use
org.apache.commons.io.IOUtils.toString() . |
static String |
toString(Reader input,
int bufferSize)
Deprecated.
use
org.apache.commons.io.IOUtils.toString() . |
@Deprecated public static void copy(@Nonnull InputStream input, @Nonnull OutputStream output) throws IOException
org.apache.commons.io.IOUtils.copy()
or in
Java 9 and later InputStream.transferTo()
.InputStream
to an OutputStream
.input
- the stream to read fromoutput
- the stream to write toIOException
- in case of an error@Deprecated public static void copy(@Nonnull InputStream input, @Nonnull OutputStream output, int bufferSize) throws IOException
org.apache.commons.io.IOUtils.copy()
or in
Java 9 and later InputStream.transferTo()
.InputStream
to an OutputStream
.
In Java 9 and later this is replaced by InputStream.transferTo()
.input
- the stream to read fromoutput
- the stream to write tobufferSize
- size of internal bufferIOException
- in case of an error@Deprecated public static void copy(@Nonnull Reader input, @Nonnull Writer output) throws IOException
Reader
to a Writer
.input
- the reader to read fromoutput
- the writer to write toIOException
- in case of failure * @deprecated use org.apache.commons.io.IOUtils.copy()
.@Deprecated public static void copy(@Nonnull Reader input, @Nonnull Writer output, int bufferSize) throws IOException
org.apache.commons.io.IOUtils.copy()
.Reader
to a Writer
.input
- the reader to read fromoutput
- the writer to write tobufferSize
- size of internal bufferIOException
- in case of failure@Deprecated public static void copy(@Nonnull InputStream input, @Nonnull Writer output) throws IOException
org.apache.commons.io.IOUtils.copy()
.InputStream
to chars on a
Writer
.
The platform's default encoding is used for the byte-to-char conversion.input
- the reader to read fromoutput
- the writer to write toIOException
- in case of failure@Deprecated public static void copy(@Nonnull InputStream input, @Nonnull Writer output, int bufferSize) throws IOException
org.apache.commons.io.IOUtils.copy()
.InputStream
to chars on a
Writer
.
The platform's default encoding is used for the byte-to-char conversion.input
- the input stream to read fromoutput
- the writer to write tobufferSize
- size of internal bufferIOException
- in case of failure@Deprecated public static void copy(@Nonnull InputStream input, @Nonnull Writer output, @Nonnull String encoding) throws IOException
org.apache.commons.io.IOUtils.copy()
.InputStream
to chars on a
Writer
, using the specified encoding.input
- the input stream to read fromoutput
- the writer to write toencoding
- the name of a supported character encoding. See the
IANA
Charset Registry for a list of valid encoding types.IOException
- in case of failure@Deprecated public static void copy(@Nonnull InputStream input, @Nonnull Writer output, @Nonnull String encoding, int bufferSize) throws IOException
org.apache.commons.io.IOUtils.copy()
.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 stream to read fromoutput
- the writer to write tobufferSize
- size of internal bufferIOException
- in case of failure@Deprecated @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 InputStream to read fromIOException
- in case of failure@Deprecated @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 InputStream to read frombufferSize
- size of internal bufferIOException
- in case of failure@Deprecated @Nonnull public static String toString(@Nonnull InputStream input, @Nonnull String encoding) throws IOException
org.apache.commons.io.IOUtils.toString()
.InputStream
as a String.input
- the InputStream to read fromencoding
- the name of a supported character encoding. See the
IANA
Charset Registry for a list of valid encoding types.IOException
- in case of failure@Deprecated @Nonnull public static String toString(@Nonnull InputStream input, @Nonnull String encoding, int bufferSize) throws IOException
org.apache.commons.io.IOUtils.toString()
.InputStream
as a String.input
- the InputStream to read fromencoding
- the name of a supported character encoding. See the
IANA
Charset Registry for a list of valid encoding types.bufferSize
- size of internal bufferIOException
- in case of failure@Deprecated @Nonnull public static byte[] toByteArray(@Nonnull InputStream input) throws IOException
org.apache.commons.io.IOUtils.readFully()
.InputStream
as a byte[]
.input
- the InputStream to read fromIOException
- in case of failure@Deprecated @Nonnull public static byte[] toByteArray(@Nonnull InputStream input, int bufferSize) throws IOException
org.apache.commons.io.IOUtils.readFully()
.InputStream
as a byte[]
.input
- the InputStream to read frombufferSize
- size of internal bufferIOException
- in case of failure@Deprecated public static void copy(@Nonnull Reader input, @Nonnull OutputStream output) throws IOException
Reader
to bytes on an OutputStream
, and
flush the OutputStream
.input
- the InputStream to read fromoutput
- the output stream to write toIOException
- in case of failure@Deprecated 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 InputStream to read fromoutput
- the output to write tobufferSize
- size of internal bufferIOException
- in case of failure@Deprecated @Nonnull public static String toString(@Nonnull Reader input) throws IOException
org.apache.commons.io.IOUtils.toString()
.Reader
as a String.input
- the InputStream to read fromIOException
- in case of failure@Deprecated @Nonnull public static String toString(@Nonnull Reader input, int bufferSize) throws IOException
org.apache.commons.io.IOUtils.toString()
.Reader
as a String.input
- the reader to read frombufferSize
- size of internal bufferIOException
- in case of failure@Deprecated @Nonnull public static byte[] toByteArray(@Nonnull Reader input) throws IOException
Reader
as a byte[]
.input
- the InputStream to read fromIOException
- in case of failure@Deprecated @Nonnull public static byte[] toByteArray(@Nonnull Reader input, int bufferSize) throws IOException
Reader
as a byte[]
.input
- the InputStream to read frombufferSize
- size of internal bufferIOException
- in case of failure@Deprecated public static void copy(@Nonnull String input, @Nonnull OutputStream output) throws IOException
String
to bytes on an OutputStream
, and
flush the OutputStream
.input
- the InputStream to read fromoutput
- the output to write toIOException
- in case of failure@Deprecated 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 InputStream to read fromoutput
- the output to write tobufferSize
- size of internal bufferIOException
- in case of failure@Deprecated public static void copy(@Nonnull String input, @Nonnull Writer output) throws IOException
org.apache.commons.io.IOUtils.write()
.String
to a Writer
.input
- the string to writeoutput
- resulting output Writer
IOException
- in case of failure@Deprecated @Nonnull public static byte[] toByteArray(@Nonnull String input) throws IOException
String
as a byte[]
.input
- the String to read fromIOException
- in case of failure@Deprecated @Nonnull public static byte[] toByteArray(@Nonnull String input, int bufferSize) throws IOException
String
as a byte[]
.input
- the InputStream to read frombufferSize
- size of internal bufferIOException
- in case of failure@Deprecated 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 InputStream to read fromoutput
- the output to write toIOException
- in case of failure@Deprecated 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 InputStream to read fromoutput
- the output to write tobufferSize
- size of internal bufferIOException
- in case of failure@Deprecated public static void copy(@Nonnull byte[] input, @Nonnull Writer output, String encoding) throws IOException
org.apache.commons.io.IOUtils.write()
.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 data to writeoutput
- the writer to write toIOException
- in case of failure@Deprecated public static void copy(@Nonnull byte[] input, @Nonnull Writer output, @Nonnull String encoding, int bufferSize) throws IOException
org.apache.commons.io.IOUtils.write()
.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 bytesoutput
- The output buffer Writer
bufferSize
- size of internal bufferIOException
- in case of failure@Deprecated @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 bytesIOException
- in case of failure@Deprecated @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 bufferinput
- the input bytesIOException
- in case of failure@Deprecated @Nonnull public static String toString(@Nonnull byte[] input, @Nonnull String encoding) throws IOException
new String(input, encoding)
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 bytesIOException
- in case of failure@Deprecated @Nonnull public static String toString(@Nonnull byte[] input, @Nonnull String encoding, int bufferSize) throws IOException
new String(input, encoding)
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 bufferinput
- input bytesIOException
- in case of failure@Deprecated public static void copy(@Nonnull byte[] input, @Nonnull OutputStream output) throws IOException
byte[]
to an OutputStream
.input
- Input byte array.output
- output stream OutputStream
IOException
- in case of failure@Deprecated public static boolean contentEquals(@Nonnull InputStream input1, @Nonnull InputStream input2) throws IOException
org.apache.commons.io.IOUtils.contentEquals()
input1
- the first streaminput2
- the second streamIOException
- in case of failure@Deprecated public static void close(@Nullable Channel channel)
Channel
suppressing any IOException
.
Note: The use case 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
IOException
s 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
.@Deprecated public static void close(@Nullable InputStream inputStream)
InputStream
suppressing any IOException
.
Note: The use case 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
IOException
s 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
.@Deprecated public static void close(@Nullable OutputStream outputStream)
OutputStream
suppressing any IOException
.
Note: The use case 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
IOException
s 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
.@Deprecated public static void close(@Nullable Reader reader)
Reader
suppressing any IOException
.
Note: The use case 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
IOException
s 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
.@Deprecated public static void close(@Nullable Writer writer)
Writer
suppressing any IOException
.
Note: The use case 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
IOException
s 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
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