javax.servlet.jsp

Class JspWriter

Known Direct Subclasses:
BodyContent

public abstract class JspWriter
extends java.io.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:
java.io.Writer, java.io.BufferedWriter, java.io.PrintWriter

Field Summary

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.
protected boolean
autoFlush
Whether the JspWriter is autoflushing.
protected int
bufferSize
The size of the buffer used by the JspWriter.

Constructor Summary

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(Object obj)
Print an object.
abstract void
print(String s)
Print a string.
abstract void
print(boolean b)
Print a boolean value.
abstract void
print(char c)
Print a character.
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(s[] )
Print an array of characters.
abstract void
println()
Terminate the current line by writing the line separator string.
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.
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(double x)
Print a double-precision floating-point number and then terminate the line.
abstract void
print