javax.servlet.jsp

Class JspWriter

java.lang.Object

java.io.Writer

javax.servlet.jsp.JspWriter

All Implemented Interfaces:

Closeable, Flushable, Appendable, AutoCloseable

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:

• Exceeding the buffer is not a fatal error; when the buffer is exceeded, just flush the output.
• Exceeding the buffer is a fatal error; when the buffer is exceeded, raise an exception.

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

Fields

Modifier and Type	Field and Description
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

Constructors

Modifier	Constructor and Description
protected	JspWriter(int bufferSize, boolean autoFlush) Protected constructor.

Method Summary

Methods

Modifier and Type	Method and Description
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 occured 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 occured 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 occured 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 occured 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 occured 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 occured 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 occured 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 occured 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 occured 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 occured 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 occured 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 occured 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 occured 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 occured 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 occured 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 occured 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 occured 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 occured 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 occured 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 interface AutoCloseable

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