File Doc Category Size Date Package
JspWriter.java API Doc Apache Tomcat 6.0.14 16482 Fri Jul 20 04:20:30 BST 2007 javax.servlet.jsp

JspWriter

java.lang.Object
- java.io.Writer

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: java.io.Writer
see: java.io.BufferedWriter
see: java.io.PrintWriter

Fields Summary
public static final int
NO_BUFFER
Constant indicating that the Writer is not buffering output.
public static final int
DEFAULT_BUFFER
Constant indicating that the Writer is buffered and is using the implementation default buffer size.
public static final int
UNBOUNDED_BUFFER
Constant indicating that the Writer is buffered and is unbounded; this is used in BodyContent.
protected int
bufferSize
The size of the buffer used by the JspWriter.
protected boolean
autoFlush
Whether the JspWriter is autoflushing.
Constructors Summary
protected JspWriter(int bufferSize, boolean autoFlush)
Protected constructor.
param
bufferSize the size of the buffer to be used by the JspWriter
param
autoFlush whether the JspWriter should be autoflushing
this.bufferSize = bufferSize; this.autoFlush = autoFlush;
Methods Summary
public abstract void clear()
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
public abstract void clearBuffer()
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
public abstract void close()
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.
exception
IOException If an I/O error occurs
public abstract void flush()
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.
exception
IOException If an I/O error occurs
public int getBufferSize()
This method returns the size of the buffer used by the JspWriter.
return
the size of the buffer in bytes, or 0 is unbuffered.
return bufferSize;
public abstract int getRemaining()
This method returns the number of unused bytes in the buffer.
return
the number of bytes unused in the buffer
public boolean isAutoFlush()
This method indicates whether the JspWriter is autoFlushing.
return
if this JspWriter is auto flushing or throwing IOExceptions on buffer overflow conditions
return autoFlush;
public abstract void newLine()
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.
exception
IOException If an I/O error occurs
public abstract void print(java.lang.String s)
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.
param
s The String to be printed
throws
java.io.IOException If an error occured while writing
public abstract void print(java.lang.Object obj)
Print an object. The string produced by the {@link java.lang.String#valueOf(Object)} method is written to the JspWriter's buffer or, if no buffer is used, directly to the underlying writer.
param
obj The Object to be printed
see
java.lang.Object#toString()
throws
java.io.IOException If an error occured while writing
public abstract void print(boolean b)
Print a boolean value. The string produced by {@link java.lang.String#valueOf(boolean)} is written to the JspWriter's buffer or, if no buffer is used, directly to the underlying writer.
param
b The boolean to be printed
throws
java.io.IOException If an error occured while writing
public abstract void print(char c)
Print a character. The character is written to the JspWriter's buffer or, if no buffer is used, directly to the underlying writer.
param
c The char to be printed
throws
java.io.IOException If an error occured while writing
public abstract void print(int i)
Print an integer. The string produced by {@link java.lang.String#valueOf(int)} is written to the JspWriter's buffer or, if no buffer is used, directly to the underlying writer.
param
i The int to be printed
see
java.lang.Integer#toString(int)
throws
java.io.IOException If an error occured while writing
public abstract void print(long l)
Print a long integer. The string produced by {@link java.lang.String#valueOf(long)} is written to the JspWriter's buffer or, if no buffer is used, directly to the underlying writer.
param
l The long to be printed
see
java.lang.Long#toString(long)
throws
java.io.IOException If an error occured while writing
public abstract void print(float f)
Print a floating-point number. The string produced by {@link java.lang.String#valueOf(float)} is written to the JspWriter's buffer or, if no buffer is used, directly to the underlying writer.
param
f The float to be printed
see
java.lang.Float#toString(float)
throws
java.io.IOException If an error occured while writing
public abstract void print(double d)
Print a double-precision floating-point number. The string produced by {@link java.lang.String#valueOf(double)} is written to the JspWriter's buffer or, if no buffer is used, directly to the underlying writer.
param
d The double to be printed
see
java.lang.Double#toString(double)
throws
java.io.IOException If an error occured while writing
public abstract void print(char[] s)
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.
param
s The array of chars to be printed
throws
NullPointerException If s is null
throws
java.io.IOException If an error occured while writing
public abstract void println()
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
java.io.IOException If an error occured while writing
public abstract void println(boolean x)
Print a boolean value and then terminate the line. This method behaves as though it invokes {@link #print(boolean)} and then {@link #println()}.
param
x the boolean to write
throws
java.io.IOException If an error occured while writing
public abstract void println(char x)
Print a character and then terminate the line. This method behaves as though it invokes {@link #print(char)} and then {@link #println()}.
param
x the char to write
throws
java.io.IOException If an error occured while writing
public abstract void println(int x)
Print an integer and then terminate the line. This method behaves as though it invokes {@link #print(int)} and then {@link #println()}.
param
x the int to write
throws
java.io.IOException If an error occured while writing
public abstract void println(long x)
Print a long integer and then terminate the line. This method behaves as though it invokes {@link #print(long)} and then {@link #println()}.
param
x the long to write
throws
java.io.IOException If an error occured while writing
public abstract void println(float x)
Print a floating-point number and then terminate the line. This method behaves as though it invokes {@link #print(float)} and then {@link #println()}.
param
x the float to write
throws
java.io.IOException If an error occured while writing
public abstract void println(double x)
Print a double-precision floating-point number and then terminate the line. This method behaves as though it invokes {@link #print(double)} and then {@link #println()}.
param
x the double to write
throws
java.io.IOException If an error occured while writing
public abstract void println(char[] x)
Print an array of characters and then terminate the line. This method behaves as though it invokes print(char[]) and then println().
param
x the char[] to write
throws
java.io.IOException If an error occured while writing
public abstract void println(java.lang.String x)
Print a String and then terminate the line. This method behaves as though it invokes {@link #print(String)} and then {@link #println()}.
param
x the String to write
throws
java.io.IOException If an error occured while writing
public abstract void println(java.lang.Object x)
Print an Object and then terminate the line. This method behaves as though it invokes {@link #print(Object)} and then {@link #println()}.
param
x the Object to write
throws
java.io.IOException If an error occured while writing