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Class JspWriter

java.lang.Object  |  +--java.io.Writer        |        +--javax.servlet.jsp.JspWriter

Direct Known Subclasses:

BodyContent

public abstract classJspWriter

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:

• 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,java.io.BufferedWriter,PrintWriter

NO_BUFFER

public static final intNO_BUFFER

constant indicating that the Writer is not buffering output

DEFAULT_BUFFER

public static final intDEFAULT_BUFFER

constant indicating that the Writer is buffered and is using the implementation default buffer size

UNBOUNDED_BUFFER

public static final intUNBOUNDED_BUFFER

constant indicating that the Writer is buffered and is unbounded; this is used in BodyContent

bufferSize

protected intbufferSize

autoFlush

protected booleanautoFlush

JspWriter

protectedJspWriter(int bufferSize,                    boolean autoFlush)

protected constructor.

newLine

public abstract voidnewLine()                      throws java.io.IOException

Write a line separator. The line separator string is defined by the system propertyline.separator, and is not necessarily a single newline ('\n') character.

Throws:

java.io.IOException - If an I/O error occurs

print

public abstract voidprint(boolean b)                    throws java.io.IOException

Print a boolean value. The string produced byString.valueOf(boolean) is translated into bytes according to the platform's default character encoding, and these bytes are written in exactly the manner of theWriter.write(int) method.

Parameters:

b - Theboolean to be printed

Throws:

java.io.IOException -  

print

public abstract voidprint(char c)                    throws java.io.IOException

Print a character. The character is translated into one or more bytes according to the platform's default character encoding, and these bytes are written in exactly the manner of theWriter.write(int) method.

Parameters:

c - Thechar to be printed

Throws:

java.io.IOException -  

print

public abstract voidprint(int i)                    throws java.io.IOException

Print an integer. The string produced byString.valueOf(int) is translated into bytes according to the platform's default character encoding, and these bytes are written in exactly the manner of theWriter.write(int) method.

Parameters:

i - Theint to be printed

Throws:

java.io.IOException -  

See Also:

java.lang.Integer#toString(int)

print

public abstract voidprint(long l)                    throws java.io.IOException

Print a long integer. The string produced byString.valueOf(long) is translated into bytes according to the platform's default character encoding, and these bytes are written in exactly the manner of theWriter.write(int) method.

Parameters:

l - Thelong to be printed

Throws:

java.io.IOException -  

See Also:

java.lang.Long#toString(long)

print

public abstract voidprint(float f)                    throws java.io.IOException

Print a floating-point number. The string produced byString.valueOf(float) is translated into bytes according to the platform's default character encoding, and these bytes are written in exactly the manner of theWriter.write(int) method.

Parameters:

f - Thefloat to be printed

Throws:

java.io.IOException -  

See Also:

java.lang.Float#toString(float)

print

public abstract voidprint(double d)                    throws java.io.IOException

Print a double-precision floating-point number. The string produced byString.valueOf(double) is translated into bytes according to the platform's default character encoding, and these bytes are written in exactly the manner of theWriter.write(int) method.

Parameters:

d - Thedouble to be printed

Throws:

java.io.IOException -  

See Also:

java.lang.Double#toString(double)

print

public abstract voidprint(char[] s)                    throws java.io.IOException

Print an array of characters. The characters are converted into bytes according to the platform's default character encoding, and these bytes are written in exactly the manner of theWriter.write(int) method.

Parameters:

s - The array of chars to be printed

Throws:

java.lang.NullPointerException - Ifs isnull

java.io.IOException -  

print

public abstract voidprint(java.lang.String s)                    throws java.io.IOException

Print a string. If the argument isnull then the string"null" is printed. Otherwise, the string's characters are converted into bytes according to the platform's default character encoding, and these bytes are written in exactly the manner of theWriter.write(int) method.

Parameters:

s - TheString to be printed

Throws:

java.io.IOException -  

print

public abstract voidprint(java.lang.Object obj)                    throws java.io.IOException

Print an object. The string produced by theString.valueOf(Object) method is translated into bytes according to the platform's default character encoding, and these bytes are written in exactly the manner of theWriter.write(int) method.

Parameters:

obj - TheObject to be printed

Throws:

java.io.IOException -  

See Also:

Object.toString()

println

public abstract voidprintln()                      throws java.io.IOException

Terminate the current line by writing the line separator string. The line separator string is defined by the system propertyline.separator, and is not necessarily a single newline character ('\n').

Throws:

java.io.IOException -  

println

public abstract voidprintln(boolean x)                      throws java.io.IOException

Print a boolean value and then terminate the line. This method behaves as though it invokesprint(boolean) and thenprintln().

Throws:

java.io.IOException -  

println

public abstract voidprintln(char x)                      throws java.io.IOException

Print a character and then terminate the line. This method behaves as though it invokesprint(char) and thenprintln().

Throws:

java.io.IOException -  

println

public abstract voidprintln(int x)                      throws java.io.IOException

Print an integer and then terminate the line. This method behaves as though it invokesprint(int) and thenprintln().

Throws:

java.io.IOException -  

println

public abstract voidprintln(long x)                      throws java.io.IOException

Print a long integer and then terminate the line. This method behaves as though it invokesprint(long) and thenprintln().

Throws:

java.io.IOException -  

println

public abstract voidprintln(float x)                      throws java.io.IOException

Print a floating-point number and then terminate the line. This method behaves as though it invokesprint(float) and thenprintln().

Throws:

java.io.IOException -  

println

public abstract voidprintln(double x)                      throws java.io.IOException

Print a double-precision floating-point number and then terminate the line. This method behaves as though it invokesprint(double) and thenprintln().

Throws:

java.io.IOException -  

println

public abstract voidprintln(char[] x)                      throws java.io.IOException

Print an array of characters and then terminate the line. This method behaves as though it invokesprint(char[]) and thenprintln().

Throws:

java.io.IOException -  

println

public abstract voidprintln(java.lang.String x)                      throws java.io.IOException

Print a String and then terminate the line. This method behaves as though it invokesprint(String) and thenprintln().

Throws:

java.io.IOException -  

println

public abstract voidprintln(java.lang.Object x)                      throws java.io.IOException

Print an Object and then terminate the line. This method behaves as though it invokesprint(Object) and thenprintln().

Throws:

java.io.IOException -  

clear

public abstract voidclear()                    throws java.io.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:

java.io.IOException - If an I/O error occurs

clearBuffer

public abstract voidclearBuffer()                          throws java.io.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:

java.io.IOException - If an I/O error occurs

flush

public abstract voidflush()                    throws java.io.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.

Overrides:

flush in classjava.io.Writer

Throws:

java.io.IOException - If an I/O error occurs

close

public abstract voidclose()                    throws java.io.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.

Overrides:

close in classjava.io.Writer

Throws:

java.io.IOException - If an I/O error occurs

getBufferSize

public intgetBufferSize()

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 intgetRemaining()

This method returns the number of unused bytes in the buffer.

Returns:

the number of bytes unused in the buffer

isAutoFlush

public booleanisAutoFlush()

This method indicates whether the JspWriter is autoFlushing.

Returns:

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