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Tomcat example source code file (JspWriter.java)

This example Tomcat source code file (JspWriter.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Java - Tomcat tags/keywords

default_buffer, default_buffer, io, ioexception, ioexception, jspwriter, jspwriter, no_buffer, unbounded_buffer, unbounded_buffer

The Tomcat JspWriter.java source code

/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements.  See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License.  You may obtain a copy of the License at
*
*     http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
 
package javax.servlet.jsp;

import java.io.IOException;

/**
 * <p>
 * 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.
 *<p>
 * 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.
 * <p>Buffering
 * <p>
 * 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.
 * <p>
 * Buffering raises the issue of what to do when the buffer is
 * exceeded. Two approaches can be taken:
 * <ul>
 * <li>
 * Exceeding the buffer is not a fatal error; when the buffer is
 * exceeded, just flush the output.
 * <li>
 * Exceeding the buffer is a fatal error; when the buffer is exceeded,
 * raise an exception.
 * </ul>
 * <p>
 * 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.
 * <p>
 * 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.
 * <p>
 * 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
 */

abstract public class JspWriter extends java.io.Writer {

    /**
     * Constant indicating that the Writer is not buffering output.
     */

    public static final int	NO_BUFFER = 0;

    /**
     * Constant indicating that the Writer is buffered and is using the
     * implementation default buffer size.
     */

    public static final int	DEFAULT_BUFFER = -1;

    /**
     * Constant indicating that the Writer is buffered and is unbounded; this
     * is used in BodyContent.
     */

    public static final int	UNBOUNDED_BUFFER = -2;

    /**
     * Protected constructor.
     *
     * @param bufferSize the size of the buffer to be used by the JspWriter
     * @param autoFlush whether the JspWriter should be autoflushing
     */

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

    /**
     * Write a line separator.  The line separator string is defined by the
     * system property <tt>line.separator, and is not necessarily a single
     * newline ('\n') character.
     *
     * @exception  IOException  If an I/O error occurs
     */

    abstract public void newLine() throws IOException;

    /**
     * Print a boolean value.  The string produced by <code>{@link
     * java.lang.String#valueOf(boolean)}</code> is written to the
     * JspWriter's buffer or, if no buffer is used, directly to the 
     * underlying writer.
     *
     * @param      b   The <code>boolean to be printed
     * @throws	   java.io.IOException If an error occured while writing
     */

    abstract public void print(boolean b) 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.
     *
     * @param      c   The <code>char to be printed
     * @throws	   java.io.IOException If an error occured while writing
     */

    abstract public void print(char c) throws IOException;

    /**
     * Print an integer.  The string produced by <code>{@link
     * java.lang.String#valueOf(int)}</code> is written to the
     * JspWriter's buffer or, if no buffer is used, directly to the
     * underlying writer.
     *
     * @param      i   The <code>int to be printed
     * @see        java.lang.Integer#toString(int)
     * @throws	   java.io.IOException If an error occured while writing
     */

    abstract public void print(int i) throws IOException;

    /**
     * Print a long integer.  The string produced by <code>{@link
     * java.lang.String#valueOf(long)}</code> is written to the
     * JspWriter's buffer or, if no buffer is used, directly to the
     * underlying writer.
     *
     * @param      l   The <code>long to be printed
     * @see        java.lang.Long#toString(long)
     * @throws	   java.io.IOException If an error occured while writing
     */

    abstract public void print(long l) throws IOException;

    /**
     * Print a floating-point number.  The string produced by <code>{@link
     * java.lang.String#valueOf(float)}</code> is written to the
     * JspWriter's buffer or, if no buffer is used, directly to the
     * underlying writer.
     *
     * @param      f   The <code>float to be printed
     * @see        java.lang.Float#toString(float)
     * @throws	   java.io.IOException If an error occured while writing
     */

    abstract public void print(float f) throws IOException;

    /**
     * Print a double-precision floating-point number.  The string produced by
     * <code>{@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 <code>double to be printed
     * @see        java.lang.Double#toString(double)
     * @throws	   java.io.IOException If an error occured while writing
     */

    abstract public void print(double d) 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.
     *
     * @param      s   The array of chars to be printed
     *
     * @throws  NullPointerException  If <code>s is null
     * @throws	   java.io.IOException If an error occured while writing
     */

    abstract public void print(char s[]) throws IOException;

    /**
     * Print a string.  If the argument is <code>null then the string
     * <code>"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 <code>String to be printed
     * @throws	   java.io.IOException If an error occured while writing
     */

    abstract public void print(String s) throws IOException;

    /**
     * Print an object.  The string produced by the <code>{@link
     * java.lang.String#valueOf(Object)}</code> method is written to the
     * JspWriter's buffer or, if no buffer is used, directly to the
     * underlying writer.
     *
     * @param      obj   The <code>Object to be printed
     * @see        java.lang.Object#toString()
     * @throws	   java.io.IOException If an error occured while writing
     */

    abstract public void print(Object obj) throws IOException;

    /**
     * Terminate the current line by writing the line separator string.  The
     * line separator string is defined by the system property
     * <code>line.separator, and is not necessarily a single newline
     * character (<code>'\n').
     * @throws	   java.io.IOException If an error occured while writing
     */

    abstract public void println() throws IOException;

    /**
     * Print a boolean value and then terminate the line.  This method behaves
     * as though it invokes <code>{@link #print(boolean)} and then
     * <code>{@link #println()}.
     *
     * @param      x the boolean to write
     * @throws	   java.io.IOException If an error occured while writing
     */

    abstract public void println(boolean x) throws IOException;

    /**
     * Print a character and then terminate the line.  This method behaves as
     * though it invokes <code>{@link #print(char)} and then {@link
     * #println()}</code>.
     *
     * @param      x the char to write
     * @throws	   java.io.IOException If an error occured while writing
     */

    abstract public void println(char x) throws IOException;

    /**
     * Print an integer and then terminate the line.  This method behaves as
     * though it invokes <code>{@link #print(int)} and then {@link
     * #println()}</code>.
     *
     * @param      x the int to write
     * @throws	   java.io.IOException If an error occured while writing
     */

    abstract public void println(int x) throws IOException;

    /**
     * Print a long integer and then terminate the line.  This method behaves
     * as though it invokes <code>{@link #print(long)} and then
     * <code>{@link #println()}.
     *
     * @param      x the long to write
     * @throws	   java.io.IOException If an error occured while writing
     */

    abstract public void println(long x) throws IOException;

    /**
     * Print a floating-point number and then terminate the line.  This method
     * behaves as though it invokes <code>{@link #print(float)} and then
     * <code>{@link #println()}.
     *
     * @param      x the float to write
     * @throws	   java.io.IOException If an error occured while writing
     */

    abstract public void println(float x) throws IOException;

    /**
     * Print a double-precision floating-point number and then terminate the
     * line.  This method behaves as though it invokes <code>{@link
     * #print(double)}</code> and then {@link #println()}.
     *
     * @param      x the double to write
     * @throws	   java.io.IOException If an error occured while writing
     */

    abstract public void println(double x) throws IOException;

    /**
     * Print an array of characters and then terminate the line.  This method
     * behaves as though it invokes <code>print(char[]) and then
     * <code>println().
     *
     * @param      x the char[] to write
     * @throws	   java.io.IOException If an error occured while writing
     */

    abstract public void println(char x[]) throws IOException;

    /**
     * Print a String and then terminate the line.  This method behaves as
     * though it invokes <code>{@link #print(String)} and then
     * <code>{@link #println()}.
     *
     * @param      x the String to write
     * @throws	   java.io.IOException If an error occured while writing
     */

    abstract public void println(String x) throws IOException;

    /**
     * Print an Object and then terminate the line.  This method behaves as
     * though it invokes <code>{@link #print(Object)} and then
     * <code>{@link #println()}.
     *
     * @param      x the Object to write
     * @throws	   java.io.IOException If an error occured while writing
     */

    abstract public void println(Object x) 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.
     *
     * @throws IOException		If an I/O error occurs
     */

    abstract public void clear() 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.
     *
     * @throws IOException		If an I/O error occurs
     */

    abstract public void clearBuffer() 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.
     * <p>
     * The method may be invoked indirectly if the buffer size is exceeded.
     * <p>
     * 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
     */

    abstract public void flush() throws IOException;

    /**
     * Close the stream, flushing it first.
     * <p>
     * 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().
     * <p>
     * Closing a previously-closed stream, unlike flush(), has no effect.
     *
     * @exception  IOException  If an I/O error occurs
     */

    abstract public void close() throws IOException;

    /**
     * This method returns the size of the buffer used by the JspWriter.
     *
     * @return the size of the buffer in bytes, or 0 is unbuffered.
     */

    public int getBufferSize() { return bufferSize; }

    /**
     * This method returns the number of unused bytes in the buffer.
     *
     * @return the number of bytes unused in the buffer
     */

    abstract public int getRemaining();

    /**
     * This method indicates whether the JspWriter is autoFlushing.
     *
     * @return if this JspWriter is auto flushing or throwing IOExceptions 
     *     on buffer overflow conditions
     */

    public boolean isAutoFlush() { return autoFlush; }

    /*
     * fields
     */

    /**
     * The size of the buffer used by the JspWriter.
     */
    protected int     bufferSize;
    
    /**
     * Whether the JspWriter is autoflushing.
     */
    protected boolean autoFlush;
}

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