Class JspWriter
- All Implemented Interfaces:
Closeable
,Flushable
,Appendable
,AutoCloseable
- Direct Known Subclasses:
BodyContent
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 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:
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Field Summary
Modifier and TypeFieldDescriptionprotected boolean
Whether the JspWriter is autoflushing.protected int
The size of the buffer used by the JspWriter.static final int
Constant indicating that the Writer is buffered and is using the implementation default buffer size.static final int
Constant indicating that the Writer is not buffering output.static final int
Constant indicating that the Writer is buffered and is unbounded; this is used in BodyContent. -
Constructor Summary
ModifierConstructorDescriptionprotected
JspWriter
(int bufferSize, boolean autoFlush) Protected constructor. -
Method Summary
Modifier and TypeMethodDescriptionabstract void
clear()
Clear the contents of the buffer.abstract void
Clears the current contents of the buffer.abstract void
close()
Close the stream, flushing it first.abstract void
flush()
Flush the stream.int
This method returns the size of the buffer used by the JspWriter.abstract int
This method returns the number of unused bytes in the buffer.boolean
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 an object.abstract void
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
Print an Object and then terminate the line.abstract void
Print a String and then terminate the line.
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Field Details
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NO_BUFFER
public static final int NO_BUFFERConstant indicating that the Writer is not buffering output.- See Also:
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DEFAULT_BUFFER
public static final int DEFAULT_BUFFERConstant indicating that the Writer is buffered and is using the implementation default buffer size.- See Also:
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UNBOUNDED_BUFFER
public static final int UNBOUNDED_BUFFERConstant indicating that the Writer is buffered and is unbounded; this is used in BodyContent.- See Also:
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bufferSize
protected int bufferSizeThe size of the buffer used by the JspWriter. -
autoFlush
protected boolean autoFlushWhether the JspWriter is autoflushing.
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Constructor Details
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JspWriter
protected JspWriter(int bufferSize, boolean autoFlush) Protected constructor.- Parameters:
bufferSize
- the size of the buffer to be used by the JspWriterautoFlush
- whether the JspWriter should be autoflushing
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Method Details
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newLine
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:
IOException
- If an I/O error occurs
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print
Print a boolean value. The string produced by
is written to the JspWriter's buffer or, if no buffer is used, directly to the underlying writer.String.valueOf(boolean)
- Parameters:
b
- Theboolean
to be printed- Throws:
IOException
- If an error occurred while writing
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print
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
- Thechar
to be printed- Throws:
IOException
- If an error occurred while writing
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print
Print an integer. The string produced by
is written to the JspWriter's buffer or, if no buffer is used, directly to the underlying writer.String.valueOf(int)
- Parameters:
i
- Theint
to be printed- Throws:
IOException
- If an error occurred while writing- See Also:
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print
Print a long integer. The string produced by
is written to the JspWriter's buffer or, if no buffer is used, directly to the underlying writer.String.valueOf(long)
- Parameters:
l
- Thelong
to be printed- Throws:
IOException
- If an error occurred while writing- See Also:
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print
Print a floating-point number. The string produced by
is written to the JspWriter's buffer or, if no buffer is used, directly to the underlying writer.String.valueOf(float)
- Parameters:
f
- Thefloat
to be printed- Throws:
IOException
- If an error occurred while writing- See Also:
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print
Print a double-precision floating-point number. The string produced by
is written to the JspWriter's buffer or, if no buffer is used, directly to the underlying writer.String.valueOf(double)
- Parameters:
d
- Thedouble
to be printed- Throws:
IOException
- If an error occurred while writing- See Also:
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print
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
- Ifs
isnull
IOException
- If an error occurred while writing
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print
Print a string. If the argument isnull
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
- TheString
to be printed- Throws:
IOException
- If an error occurred while writing
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print
Print an object. The string produced by the
method is written to the JspWriter's buffer or, if no buffer is used, directly to the underlying writer.String.valueOf(Object)
- Parameters:
obj
- TheObject
to be printed- Throws:
IOException
- If an error occurred while writing- See Also:
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println
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:
IOException
- If an error occurred while writing
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println
Print a boolean value and then terminate the line. This method behaves as though it invokes
and thenprint(boolean)
.println()
- Parameters:
x
- the boolean to write- Throws:
IOException
- If an error occurred while writing
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println
Print a character and then terminate the line. This method behaves as though it invokes
and thenprint(char)
.println()
- Parameters:
x
- the char to write- Throws:
IOException
- If an error occurred while writing
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println
Print an integer and then terminate the line. This method behaves as though it invokes
and thenprint(int)
.println()
- Parameters:
x
- the int to write- Throws:
IOException
- If an error occurred while writing
-
println
Print a long integer and then terminate the line. This method behaves as though it invokes
and thenprint(long)
.println()
- Parameters:
x
- the long to write- Throws:
IOException
- If an error occurred while writing
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println
Print a floating-point number and then terminate the line. This method behaves as though it invokes
and thenprint(float)
.println()
- Parameters:
x
- the float to write- Throws:
IOException
- If an error occurred while writing
-
println
Print a double-precision floating-point number and then terminate the line. This method behaves as though it invokes
and thenprint(double)
.println()
- Parameters:
x
- the double to write- Throws:
IOException
- If an error occurred while writing
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println
Print an array of characters and then terminate the line. This method behaves as though it invokesprint(char[])
and thenprintln()
.- Parameters:
x
- the char[] to write- Throws:
IOException
- If an error occurred while writing
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println
Print a String and then terminate the line. This method behaves as though it invokes
and thenprint(String)
.println()
- Parameters:
x
- the String to write- Throws:
IOException
- If an error occurred while writing
-
println
Print an Object and then terminate the line. This method behaves as though it invokes
and thenprint(Object)
.println()
- Parameters:
x
- the Object to write- Throws:
IOException
- If an error occurred while writing
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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
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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
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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.
- Specified by:
flush
in interfaceFlushable
- Specified by:
flush
in classWriter
- Throws:
IOException
- If an I/O error occurs
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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.
- Specified by:
close
in interfaceAutoCloseable
- Specified by:
close
in interfaceCloseable
- Specified by:
close
in classWriter
- Throws:
IOException
- If an I/O error occurs
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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.
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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
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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
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