java/jakarta/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 jakarta.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 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
 */
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 auto flushing
     */
    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.
     * <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
     */
    @Override
    public abstract 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
     */
    @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 auto flushing.
     */
    protected boolean autoFlush;
}