javax.servlet.jsp: abstract public class: JspWriter

javax.servlet.jsp
abstract public class: JspWriter [javadoc | source]

java.lang.Object
   java.io.Writer
      javax.servlet.jsp.JspWriter

All Implemented Interfaces:
Closeable, Flushable, Appendable

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 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.

Also see:

java.io.Writer

java.io.BufferedWriter

java.io.PrintWriter

Field 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.

Fields inherited from java.io.Writer:
lock

Constructor:

Constructor:
protected JspWriter(int bufferSize, boolean autoFlush) { this.bufferSize = bufferSize; this.autoFlush = autoFlush; } Protected constructor. Parameters: `bufferSize` - the size of the buffer to be used by the JspWriter `autoFlush` - whether the JspWriter should be autoflushing

 protected JspWriter(int bufferSize,
    boolean autoFlush) {
	this.bufferSize = bufferSize;
	this.autoFlush  = autoFlush;
}

Protected constructor.

Parameters:

bufferSize - the size of the buffer to be used by the JspWriter

autoFlush - whether the JspWriter should be autoflushing

Method from javax.servlet.jsp.JspWriter Summary:
clear, clearBuffer, close, flush, getBufferSize, getRemaining, isAutoFlush, newLine, print, print, print, print, print, print, print, print, print, println, println, println, println, println, println, println, println, println, println

Methods from java.io.Writer:
append, append, append, append, append, append, close, flush, write, write, write, write, write

Methods from java.lang.Object:
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method from javax.servlet.jsp.JspWriter Detail:
abstract public void clear() throws 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.
abstract public void clearBuffer() throws 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.
abstract public void close() throws 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.
abstract public void flush() throws 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.
public int getBufferSize() { return bufferSize; } This method returns the size of the buffer used by the JspWriter.
abstract public int getRemaining() This method returns the number of unused bytes in the buffer.
public boolean isAutoFlush() { return autoFlush; } This method indicates whether the JspWriter is autoFlushing.
abstract public void newLine() throws IOException 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.
abstract public void print(boolean b) throws IOException Print a boolean value. The string produced by `java.lang.String#valueOf(boolean)` is written to the JspWriter's buffer or, if no buffer is used, directly to the underlying writer.
abstract public void print(char c) throws IOException Print a character. The character is written to the JspWriter's buffer or, if no buffer is used, directly to the underlying writer.
abstract public void print(int i) throws IOException Print an integer. The string produced by `java.lang.String#valueOf(int)` is written to the JspWriter's buffer or, if no buffer is used, directly to the underlying writer.
abstract public void print(long l) throws IOException Print a long integer. The string produced by `java.lang.String#valueOf(long)` is written to the JspWriter's buffer or, if no buffer is used, directly to the underlying writer.
abstract public void print(float f) throws IOException Print a floating-point number. The string produced by `java.lang.String#valueOf(float)` is written to the JspWriter's buffer or, if no buffer is used, directly to the underlying writer.
abstract public void print(double d) throws IOException Print a double-precision floating-point number. The string produced by `java.lang.String#valueOf(double)` is written to the JspWriter's buffer or, if no buffer is used, directly to the underlying writer.
abstract public void print(char[] s) throws IOException 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.
abstract public void print(String s) throws IOException 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.
abstract public void print(Object obj) throws IOException Print an object. The string produced by the `java.lang.String#valueOf(Object)` method is written to the JspWriter's buffer or, if no buffer is used, directly to the underlying writer.
abstract public void println() throws IOException 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'`).
abstract public void println(boolean x) throws IOException Print a boolean value and then terminate the line. This method behaves as though it invokes `#print(boolean)` and then `#println()` .
abstract public void println(char x) throws IOException Print a character and then terminate the line. This method behaves as though it invokes `#print(char)` and then `#println()` .
abstract public void println(int x) throws IOException Print an integer and then terminate the line. This method behaves as though it invokes `#print(int)` and then `#println()` .
abstract public void println(long x) throws IOException Print a long integer and then terminate the line. This method behaves as though it invokes `#print(long)` and then `#println()` .
abstract public void println(float x) throws IOException Print a floating-point number and then terminate the line. This method behaves as though it invokes `#print(float)` and then `#println()` .
abstract public void println(double x) throws IOException Print a double-precision floating-point number and then terminate the line. This method behaves as though it invokes `#print(double)` and then `#println()` .
abstract public void println(char[] x) throws IOException Print an array of characters and then terminate the line. This method behaves as though it invokes `print(char[])` and then `println()`.
abstract public void println(String x) throws IOException Print a String and then terminate the line. This method behaves as though it invokes `#print(String)` and then `#println()` .
abstract public void println(Object x) throws IOException Print an Object and then terminate the line. This method behaves as though it invokes `#print(Object)` and then `#println()` .