Java tutorial
/* * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS HEADER. * * Copyright (c) 1997-2010 Oracle and/or its affiliates. All rights reserved. * * The contents of this file are subject to the terms of either the GNU * General Public License Version 2 only ("GPL") or the Common Development * and Distribution License("CDDL") (collectively, the "License"). You * may not use this file except in compliance with the License. You can * obtain a copy of the License at * https://glassfish.dev.java.net/public/CDDL+GPL_1_1.html * or packager/legal/LICENSE.txt. See the License for the specific * language governing permissions and limitations under the License. * * When distributing the software, include this License Header Notice in each * file and include the License file at packager/legal/LICENSE.txt. * * GPL Classpath Exception: * Oracle designates this particular file as subject to the "Classpath" * exception as provided by Oracle in the GPL Version 2 section of the License * file that accompanied this code. * * Modifications: * If applicable, add the following below the License Header, with the fields * enclosed by brackets [] replaced by your own identifying information: * "Portions Copyright [year] [name of copyright owner]" * * Contributor(s): * If you wish your version of this file to be governed by only the CDDL or * only the GPL Version 2, indicate your decision by adding "[Contributor] * elects to include this software in this distribution under the [CDDL or GPL * Version 2] license." If you don't indicate a single choice of license, a * recipient has the option to distribute your version of this file under * either the CDDL, the GPL Version 2 or to extend the choice of license to * its licensees as provided above. However, if you add GPL Version 2 code * and therefore, elected the GPL Version 2 license, then the option applies * only if the new code is made subject to such option by the copyright * holder. * * * This file incorporates work covered by the following copyright and * permission notice: * * Copyright 2004 The Apache Software Foundation * * Licensed 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; }