Quelle JspWriter.java Sprache: 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 jakarta.servlet.jsp;

import java.io.IOException;

/**
* 
* 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:
* <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>
* 
* 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 java.io.Writer
* @see java.io.BufferedWriter
* @see java.io.PrintWriter
*/
public abstract 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 <code>line.separator</code>,
 * and is not necessarily a single newline ('\n') character.
 *
 * @exception IOException If an I/O error occurs
 */
 public abstract void newLine() throws IOException;

 /**
 * Print a boolean value. The string produced by <code>{@link
 * 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 IOException If an error occurred while writing
 */
 public abstract 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 IOException If an error occurred while writing
 */
 public abstract void print(char c) throws IOException;

 /**
 * Print an integer. The string produced by <code>{@link
 * 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 IOException If an error occurred while writing
 */
 public abstract void print(int i) throws IOException;

 /**
 * Print a long integer. The string produced by <code>{@link
 * 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 IOException If an error occurred while writing
 */
 public abstract void print(long l) throws IOException;

 /**
 * Print a floating-point number. The string produced by <code>{@link
 * 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 IOException If an error occurred while writing
 */
 public abstract void print(float f) throws IOException;

 /**
 * Print a double-precision floating-point number. The string produced by
 * <code>{@link 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 IOException If an error occurred while writing
 */
 public abstract 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 IOException If an error occurred while writing
 */
 public abstract 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 IOException If an error occurred while writing
 */
 public abstract void print(String s) throws IOException;

 /**
 * Print an object. The string produced by the <code>{@link
 * 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 IOException If an error occurred while writing
 */
 public abstract 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 IOException If an error occurred while writing
 */
 public abstract 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 IOException If an error occurred while writing
 */
 public abstract 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 IOException If an error occurred while writing
 */
 public abstract 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 IOException If an error occurred while writing
 */
 public abstract 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 IOException If an error occurred while writing
 */
 public abstract 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 IOException If an error occurred while writing
 */
 public abstract 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 IOException If an error occurred while writing
 */
 public abstract 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 IOException If an error occurred while writing
 */
 public abstract 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 IOException If an error occurred while writing
 */
 public abstract 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 IOException If an error occurred while writing
 */
 public abstract 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
 */
 public abstract 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
 */
 public abstract 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.
 * 
 * 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.
 *
 * @exception IOException If an I/O error occurs
 */
 @Override
 public abstract void flush() 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.
 *
 * @exception IOException If an I/O error occurs
 */
 @Override
 public abstract 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
 */
 public abstract 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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