javax.servlet.jsp
Class JspWriter

java.lang.Object
  extended by java.io.Writer
      extended by javax.servlet.jsp.JspWriter
All Implemented Interfaces:
Closeable, Flushable, Appendable
Direct Known Subclasses:
BodyContent

public abstract class JspWriter
extends Writer

The actions and template data in a JSP page is written using the JspWriter object that is referenced by the implicit variable out which is initialized automatically using methods in the PageContext object.

This abstract class emulates some of the functionality found in the java.io.BufferedWriter and java.io.PrintWriter classes, however it differs in that it throws java.io.IOException from the print methods while PrintWriter does not.

Buffering

The initial JspWriter object is associated with the PrintWriter object of the ServletResponse in a way that depends on whether the page is or is not buffered. If the page is not buffered, output written to this JspWriter object will be written through to the PrintWriter directly, which will be created if necessary by invoking the getWriter() method on the response object. But if the page is buffered, the PrintWriter object will not be created until the buffer is flushed and operations like setContentType() are legal. Since this flexibility simplifies programming substantially, buffering is the default for JSP pages.

Buffering raises the issue of what to do when the buffer is exceeded. Two approaches can be taken:

Both approaches are valid, and thus both are supported in the JSP technology. The behavior of a page is controlled by the autoFlush attribute, which defaults to true. In general, JSP pages that need to be sure that correct and complete data has been sent to their client may want to set autoFlush to false, with a typical case being that where the client is an application itself. On the other hand, JSP pages that send data that is meaningful even when partially constructed may want to set autoFlush to true; such as when the data is sent for immediate display through a browser. Each application will need to consider their specific needs.

An alternative considered was to make the buffer size unbounded; but, this had the disadvantage that runaway computations would consume an unbounded amount of resources.

The "out" implicit variable of a JSP implementation class is of this type. If the page directive selects autoflush="true" then all the I/O operations on this class shall automatically flush the contents of the buffer if an overflow condition would result if the current operation were performed without a flush. If autoflush="false" then all the I/O operations on this class shall throw an IOException if performing the current operation would result in a buffer overflow condition.

See Also:
Writer, BufferedWriter, PrintWriter

Field Summary
protected  boolean autoFlush
          Whether the JspWriter is autoflushing.
protected  int bufferSize
          The size of the buffer used by the JspWriter.
static int DEFAULT_BUFFER
          Constant indicating that the Writer is buffered and is using the implementation default buffer size.
static int NO_BUFFER
          Constant indicating that the Writer is not buffering output.
static int UNBOUNDED_BUFFER
          Constant indicating that the Writer is buffered and is unbounded; this is used in BodyContent.
 
Fields inherited from class java.io.Writer
lock
 
Constructor Summary
protected JspWriter(int bufferSize, boolean autoFlush)
          Protected constructor.
 
Method Summary
abstract  void clear()
          Clear the contents of the buffer.
abstract  void clearBuffer()
          Clears the current contents of the buffer.
abstract  void close()
          Close the stream, flushing it first.
abstract  void flush()
          Flush the stream.
 int getBufferSize()
          This method returns the size of the buffer used by the JspWriter.
abstract  int getRemaining()
          This method returns the number of unused bytes in the buffer.
 boolean isAutoFlush()
          This method indicates whether the JspWriter is autoFlushing.
abstract  void newLine()
          Write a line separator.
abstract  void print(boolean b)
          Print a boolean value.
abstract  void print(char c)
          Print a character.
abstract  void print(char[] s)
          Print an array of characters.
abstract  void print(double d)
          Print a double-precision floating-point number.
abstract  void print(float f)
          Print a floating-point number.
abstract  void print(int i)
          Print an integer.
abstract  void print(long l)
          Print a long integer.
abstract  void print(Object obj)
          Print an object.
abstract  void print(String s)
          Print a string.
abstract  void println()
          Terminate the current line by writing the line separator string.
abstract  void println(boolean x)
          Print a boolean value and then terminate the line.
abstract  void println(char x)
          Print a character and then terminate the line.
abstract  void println(char[] x)
          Print an array of characters and then terminate the line.
abstract  void println(double x)
          Print a double-precision floating-point number and then terminate the line.
abstract  void println(float x)
          Print a floating-point number and then terminate the line.
abstract  void println(int x)
          Print an integer and then terminate the line.
abstract  void println(long x)
          Print a long integer and then terminate the line.
abstract  void println(Object x)
          Print an Object and then terminate the line.
abstract  void println(String x)
          Print a String and then terminate the line.
 
Methods inherited from class java.io.Writer
append, append, append, write, write, write, write, write
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Field Detail

NO_BUFFER

public static final int NO_BUFFER
Constant indicating that the Writer is not buffering output.

See Also:
Constant Field Values

DEFAULT_BUFFER

public static final int DEFAULT_BUFFER
Constant indicating that the Writer is buffered and is using the implementation default buffer size.

See Also:
Constant Field Values

UNBOUNDED_BUFFER

public static final int UNBOUNDED_BUFFER
Constant indicating that the Writer is buffered and is unbounded; this is used in BodyContent.

See Also:
Constant Field Values

bufferSize

protected int bufferSize
The size of the buffer used by the JspWriter.


autoFlush

protected boolean autoFlush
Whether the JspWriter is autoflushing.

Constructor Detail

JspWriter

protected JspWriter(int bufferSize,
                    boolean autoFlush)
Protected constructor.

Parameters:
bufferSize - the size of the buffer to be used by the JspWriter
autoFlush - whether the JspWriter should be autoflushing
Method Detail

newLine

public abstract void newLine()
                      throws IOException
Write a line separator. The line separator string is defined by the system property line.separator, and is not necessarily a single newline ('\n') character.

Throws:
IOException - If an I/O error occurs

print

public abstract void print(boolean b)
                    throws IOException
Print a boolean value. The string produced by String.valueOf(boolean) is written to the JspWriter's buffer or, if no buffer is used, directly to the underlying writer.

Parameters:
b - The boolean to be printed
Throws:
IOException - If an error occurred while writing

print

public abstract void print(char c)
                    throws IOException
Print a character. The character is written to the JspWriter's buffer or, if no buffer is used, directly to the underlying writer.

Parameters:
c - The char to be printed
Throws:
IOException - If an error occurred while writing

print

public abstract void print(int i)
                    throws IOException
Print an integer. The string produced by String.valueOf(int) is written to the JspWriter's buffer or, if no buffer is used, directly to the underlying writer.

Parameters:
i - The int to be printed
Throws:
IOException - If an error occurred while writing
See Also:
Integer.toString(int)

print

public abstract void print(long l)
                    throws IOException
Print a long integer. The string produced by String.valueOf(long) is written to the JspWriter's buffer or, if no buffer is used, directly to the underlying writer.

Parameters:
l - The long to be printed
Throws:
IOException - If an error occurred while writing
See Also:
Long.toString(long)

print

public abstract void print(float f)
                    throws IOException
Print a floating-point number. The string produced by String.valueOf(float) is written to the JspWriter's buffer or, if no buffer is used, directly to the underlying writer.

Parameters:
f - The float to be printed
Throws:
IOException - If an error occurred while writing
See Also:
Float.toString(float)

print

public abstract void print(double d)
                    throws IOException
Print a double-precision floating-point number. The string produced by String.valueOf(double) is written to the JspWriter's buffer or, if no buffer is used, directly to the underlying writer.

Parameters:
d - The double to be printed
Throws:
IOException - If an error occurred while writing
See Also:
Double.toString(double)

print

public abstract void print(char[] s)
                    throws IOException
Print an array of characters. The characters are written to the JspWriter's buffer or, if no buffer is used, directly to the underlying writer.

Parameters:
s - The array of chars to be printed
Throws:
NullPointerException - If s is null
IOException - If an error occurred while writing

print

public abstract void print(String s)
                    throws IOException
Print a string. If the argument is null then the string "null" is printed. Otherwise, the string's characters are written to the JspWriter's buffer or, if no buffer is used, directly to the underlying writer.

Parameters:
s - The String to be printed
Throws:
IOException - If an error occurred while writing

print

public abstract void print(Object obj)
                    throws IOException
Print an object. The string produced by the String.valueOf(Object) method is written to the JspWriter's buffer or, if no buffer is used, directly to the underlying writer.

Parameters:
obj - The Object to be printed
Throws:
IOException - If an error occurred while writing
See Also:
Object.toString()

println

public abstract void println()
                      throws IOException
Terminate the current line by writing the line separator string. The line separator string is defined by the system property line.separator, and is not necessarily a single newline character ('\n').

Throws:
IOException - If an error occurred while writing

println

public abstract void println(boolean x)
                      throws IOException
Print a boolean value and then terminate the line. This method behaves as though it invokes print(boolean) and then println().

Parameters:
x - the boolean to write
Throws:
IOException - If an error occurred while writing

println

public abstract void println(char x)
                      throws IOException
Print a character and then terminate the line. This method behaves as though it invokes print(char) and then println().

Parameters:
x - the char to write
Throws:
IOException - If an error occurred while writing

println

public abstract void println(int x)
                      throws IOException
Print an integer and then terminate the line. This method behaves as though it invokes print(int) and then println().

Parameters:
x - the int to write
Throws:
IOException - If an error occurred while writing

println

public abstract void println(long x)
                      throws IOException
Print a long integer and then terminate the line. This method behaves as though it invokes print(long) and then println().

Parameters:
x - the long to write
Throws:
IOException - If an error occurred while writing

println

public abstract void println(float x)
                      throws IOException
Print a floating-point number and then terminate the line. This method behaves as though it invokes print(float) and then println().

Parameters:
x - the float to write
Throws:
IOException - If an error occurred while writing

println

public abstract void println(double x)
                      throws IOException
Print a double-precision floating-point number and then terminate the line. This method behaves as though it invokes print(double) and then println().

Parameters:
x - the double to write
Throws:
IOException - If an error occurred while writing

println

public abstract void println(char[] x)
                      throws IOException
Print an array of characters and then terminate the line. This method behaves as though it invokes print(char[]) and then println().

Parameters:
x - the char[] to write
Throws:
IOException - If an error occurred while writing

println

public abstract void println(String x)
                      throws IOException
Print a String and then terminate the line. This method behaves as though it invokes print(String) and then println().

Parameters:
x - the String to write
Throws:
IOException - If an error occurred while writing

println

public abstract void println(Object x)
                      throws IOException
Print an Object and then terminate the line. This method behaves as though it invokes print(Object) and then println().

Parameters:
x - the Object to write
Throws:
IOException - If an error occurred while writing

clear

public abstract void clear()
                    throws IOException
Clear the contents of the buffer. If the buffer has been already been flushed then the clear operation shall throw an IOException to signal the fact that some data has already been irrevocably written to the client response stream.

Throws:
IOException - If an I/O error occurs

clearBuffer

public abstract void clearBuffer()
                          throws IOException
Clears the current contents of the buffer. Unlike clear(), this method will not throw an IOException if the buffer has already been flushed. It merely clears the current content of the buffer and returns.

Throws:
IOException - If an I/O error occurs

flush

public abstract void flush()
                    throws IOException
Flush the stream. If the stream has saved any characters from the various write() methods in a buffer, write them immediately to their intended destination. Then, if that destination is another character or byte stream, flush it. Thus one flush() invocation will flush all the buffers in a chain of Writers and OutputStreams.

The method may be invoked indirectly if the buffer size is exceeded.

Once a stream has been closed, further write() or flush() invocations will cause an IOException to be thrown.

Specified by:
flush in interface Flushable
Specified by:
flush in class Writer
Throws:
IOException - If an I/O error occurs

close

public abstract void close()
                    throws IOException
Close the stream, flushing it first.

This method needs not be invoked explicitly for the initial JspWriter as the code generated by the JSP container will automatically include a call to close().

Closing a previously-closed stream, unlike flush(), has no effect.

Specified by:
close in interface Closeable
Specified by:
close in class Writer
Throws:
IOException - If an I/O error occurs

getBufferSize

public int getBufferSize()
This method returns the size of the buffer used by the JspWriter.

Returns:
the size of the buffer in bytes, or 0 is unbuffered.

getRemaining

public abstract int getRemaining()
This method returns the number of unused bytes in the buffer.

Returns:
the number of bytes unused in the buffer

isAutoFlush

public boolean isAutoFlush()
This method indicates whether the JspWriter is autoFlushing.

Returns:
if this JspWriter is auto flushing or throwing IOExceptions on buffer overflow conditions

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As of July 2010, there were no online versions of the servlet 3.0, JSP 2.2, and EL 2.2 Javadocs, except as part of the huge Java EE 6 API. So, I built them myself from the Tomcat 7 source code.

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