servletapi/jsr152/src/share/javax/servlet/jsp/JspWriter.java

/*
* 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><B>Buffering</B>
 * <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</tt>, 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</code> 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</code> 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</code> 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</code> 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</code> 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)}</code> is written to
     * the JspWriter's buffer or, if no buffer is used, directly to the
     * underlying writer.
     *
     * @param      d   The <code>double</code> 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</code> is <code>null</code>
     * @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</code> then the string
     * <code>"null"</code> 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</code> 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</code> 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</code>, and is not necessarily a single newline
     * character (<code>'\n'</code>).
     * @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)}</code> and then
     * <code>{@link #println()}</code>.
     *
     * @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)}</code> and then <code>{@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)}</code> and then <code>{@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)}</code> and then
     * <code>{@link #println()}</code>.
     *
     * @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)}</code> and then
     * <code>{@link #println()}</code>.
     *
     * @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 <code>{@link #println()}</code>.
     *
     * @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[])</code> and then
     * <code>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 a String and then terminate the line.  This method behaves as
     * though it invokes <code>{@link #print(String)}</code> and then
     * <code>{@link #println()}</code>.
     *
     * @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)}</code> and then
     * <code>{@link #println()}</code>.
     *
     * @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;
}