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java.lang.Object | +--java.io.Writer | +--javax.servlet.jsp.JspWriter
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.
Writer
,
BufferedWriter
,
PrintWriter
Field Summary | |
protected boolean |
autoFlush
|
protected int |
bufferSize
|
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 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(). |
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(java.lang.Object obj)
Print an object. |
abstract void |
print(java.lang.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(java.lang.Object x)
Print an Object and then terminate the line. |
abstract void |
println(java.lang.String x)
Print a String and then terminate the line. |
Methods inherited from class java.io.Writer |
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 |
public static final int NO_BUFFER
public static final int DEFAULT_BUFFER
public static final int UNBOUNDED_BUFFER
protected int bufferSize
protected boolean autoFlush
Constructor Detail |
protected JspWriter(int bufferSize, boolean autoFlush)
Method Detail |
public abstract void newLine() throws java.io.IOException
java.io.IOException
- If an I/O error occurspublic abstract void print(boolean b) throws java.io.IOException
String.valueOf(boolean)
is translated into bytes
according to the platform's default character encoding, and these bytes
are written in exactly the manner of the Writer.write(int)
method.
b
- The boolean
to be printed
java.io.IOException
public abstract void print(char c) throws java.io.IOException
Writer.write(int)
method.
c
- The char
to be printed
java.io.IOException
public abstract void print(int i) throws java.io.IOException
String.valueOf(int)
is translated into bytes according
to the platform's default character encoding, and these bytes are
written in exactly the manner of the Writer.write(int)
method.
i
- The int
to be printed
java.io.IOException
Integer.toString(int)
public abstract void print(long l) throws java.io.IOException
String.valueOf(long)
is translated into bytes
according to the platform's default character encoding, and these bytes
are written in exactly the manner of the Writer.write(int)
method.
l
- The long
to be printed
java.io.IOException
Long.toString(long)
public abstract void print(float f) throws java.io.IOException
String.valueOf(float)
is translated into bytes
according to the platform's default character encoding, and these bytes
are written in exactly the manner of the Writer.write(int)
method.
f
- The float
to be printed
java.io.IOException
Float.toString(float)
public abstract void print(double d) throws java.io.IOException
String.valueOf(double)
is translated into
bytes according to the platform's default character encoding, and these
bytes are written in exactly the manner of the Writer.write(int)
method.
d
- The double
to be printed
java.io.IOException
Double.toString(double)
public abstract void print(char[] s) throws java.io.IOException
Writer.write(int)
method.
s
- The array of chars to be printed
java.lang.NullPointerException
- If s
is null
java.io.IOException
public abstract void print(java.lang.String s) throws java.io.IOException
null
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 the
Writer.write(int)
method.
s
- The String
to be printed
java.io.IOException
public abstract void print(java.lang.Object obj) throws java.io.IOException
String.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 the Writer.write(int)
method.
obj
- The Object
to be printed
java.io.IOException
Object.toString()
public abstract void println() throws java.io.IOException
line.separator
, and is not necessarily a single newline
character ('\n'
).
java.io.IOException
public abstract void println(boolean x) throws java.io.IOException
print(boolean)
and then
println()
.
java.io.IOException
public abstract void println(char x) throws java.io.IOException
print(char)
and then println()
.
java.io.IOException
public abstract void println(int x) throws java.io.IOException
print(int)
and then println()
.
java.io.IOException
public abstract void println(long x) throws java.io.IOException
print(long)
and then
println()
.
java.io.IOException
public abstract void println(float x) throws java.io.IOException
print(float)
and then
println()
.
java.io.IOException
public abstract void println(double x) throws java.io.IOException
print(double)
and then println()
.
java.io.IOException
public abstract void println(char[] x) throws java.io.IOException
print(char[])
and then
println()
.
java.io.IOException
public abstract void println(java.lang.String x) throws java.io.IOException
print(String)
and then
println()
.
java.io.IOException
public abstract void println(java.lang.Object x) throws java.io.IOException
print(Object)
and then
println()
.
java.io.IOException
public abstract void clear() throws java.io.IOException
java.io.IOException
- If an I/O error occurspublic abstract void clearBuffer() throws java.io.IOException
java.io.IOException
- If an I/O error occurspublic abstract void flush() throws java.io.IOException
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.
flush
in class java.io.Writer
java.io.IOException
- If an I/O error occurspublic abstract void close() throws java.io.IOException
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.
close
in class java.io.Writer
java.io.IOException
- If an I/O error occurspublic int getBufferSize()
public abstract int getRemaining()
public boolean isAutoFlush()
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