459 lines
16 KiB
Java
459 lines
16 KiB
Java
/*
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* Licensed to the Apache Software Foundation (ASF) under one or more
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* contributor license agreements. See the NOTICE file distributed with
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* this work for additional information regarding copyright ownership.
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* The ASF licenses this file to You under the Apache License, Version 2.0
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* (the "License"); you may not use this file except in compliance with
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* the License. You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package javax.servlet.jsp;
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import java.io.IOException;
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/**
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* <p>
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* The actions and template data in a JSP page is written using the JspWriter
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* object that is referenced by the implicit variable out which is initialized
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* automatically using methods in the PageContext object.
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*<p>
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* This abstract class emulates some of the functionality found in the
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* java.io.BufferedWriter and java.io.PrintWriter classes, however it differs in
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* that it throws java.io.IOException from the print methods while PrintWriter
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* does not.
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* <p>
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* <B>Buffering</B>
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* <p>
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* The initial JspWriter object is associated with the PrintWriter object of the
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* ServletResponse in a way that depends on whether the page is or is not
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* buffered. If the page is not buffered, output written to this JspWriter
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* object will be written through to the PrintWriter directly, which will be
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* created if necessary by invoking the getWriter() method on the response
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* object. But if the page is buffered, the PrintWriter object will not be
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* created until the buffer is flushed and operations like setContentType() are
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* legal. Since this flexibility simplifies programming substantially, buffering
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* is the default for JSP pages.
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* <p>
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* Buffering raises the issue of what to do when the buffer is exceeded. Two
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* approaches can be taken:
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* <ul>
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* <li>Exceeding the buffer is not a fatal error; when the buffer is exceeded,
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* just flush the output.
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* <li>Exceeding the buffer is a fatal error; when the buffer is exceeded, raise
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* an exception.
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* </ul>
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* <p>
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* Both approaches are valid, and thus both are supported in the JSP technology.
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* The behavior of a page is controlled by the autoFlush attribute, which
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* defaults to true. In general, JSP pages that need to be sure that correct and
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* complete data has been sent to their client may want to set autoFlush to
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* false, with a typical case being that where the client is an application
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* itself. On the other hand, JSP pages that send data that is meaningful even
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* when partially constructed may want to set autoFlush to true; such as when
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* the data is sent for immediate display through a browser. Each application
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* will need to consider their specific needs.
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* <p>
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* An alternative considered was to make the buffer size unbounded; but, this
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* had the disadvantage that runaway computations would consume an unbounded
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* amount of resources.
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* <p>
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* The "out" implicit variable of a JSP implementation class is of this type. If
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* the page directive selects autoflush="true" then all the I/O operations on
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* this class shall automatically flush the contents of the buffer if an
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* overflow condition would result if the current operation were performed
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* without a flush. If autoflush="false" then all the I/O operations on this
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* class shall throw an IOException if performing the current operation would
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* result in a buffer overflow condition.
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*
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* @see java.io.Writer
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* @see java.io.BufferedWriter
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* @see java.io.PrintWriter
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*/
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public abstract class JspWriter extends java.io.Writer {
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/**
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* Constant indicating that the Writer is not buffering output.
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*/
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public static final int NO_BUFFER = 0;
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/**
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* Constant indicating that the Writer is buffered and is using the
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* implementation default buffer size.
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*/
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public static final int DEFAULT_BUFFER = -1;
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/**
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* Constant indicating that the Writer is buffered and is unbounded; this is
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* used in BodyContent.
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*/
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public static final int UNBOUNDED_BUFFER = -2;
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/**
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* Protected constructor.
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*
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* @param bufferSize
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* the size of the buffer to be used by the JspWriter
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* @param autoFlush
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* whether the JspWriter should be autoflushing
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*/
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protected JspWriter(int bufferSize, boolean autoFlush) {
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this.bufferSize = bufferSize;
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this.autoFlush = autoFlush;
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}
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/**
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* Write a line separator. The line separator string is defined by the
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* system property <code>line.separator</code>, and is not necessarily a
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* single newline ('\n') character.
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*
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* @exception IOException
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* If an I/O error occurs
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*/
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public abstract void newLine() throws IOException;
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/**
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* Print a boolean value. The string produced by <code>{@link
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* java.lang.String#valueOf(boolean)}</code>
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* is written to the JspWriter's buffer or, if no buffer is used, directly
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* to the underlying writer.
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*
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* @param b
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* The <code>boolean</code> to be printed
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* @throws java.io.IOException
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* If an error occurred while writing
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*/
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public abstract void print(boolean b) throws IOException;
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/**
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* Print a character. The character is written to the JspWriter's buffer or,
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* if no buffer is used, directly to the underlying writer.
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*
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* @param c
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* The <code>char</code> to be printed
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* @throws java.io.IOException
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* If an error occurred while writing
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*/
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public abstract void print(char c) throws IOException;
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/**
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* Print an integer. The string produced by <code>{@link
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* java.lang.String#valueOf(int)}</code>
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* is written to the JspWriter's buffer or, if no buffer is used, directly
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* to the underlying writer.
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*
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* @param i
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* The <code>int</code> to be printed
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* @see java.lang.Integer#toString(int)
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* @throws java.io.IOException
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* If an error occurred while writing
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*/
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public abstract void print(int i) throws IOException;
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/**
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* Print a long integer. The string produced by <code>{@link
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* java.lang.String#valueOf(long)}</code>
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* is written to the JspWriter's buffer or, if no buffer is used, directly
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* to the underlying writer.
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*
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* @param l
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* The <code>long</code> to be printed
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* @see java.lang.Long#toString(long)
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* @throws java.io.IOException
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* If an error occurred while writing
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*/
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public abstract void print(long l) throws IOException;
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/**
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* Print a floating-point number. The string produced by <code>{@link
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* java.lang.String#valueOf(float)}</code>
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* is written to the JspWriter's buffer or, if no buffer is used, directly
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* to the underlying writer.
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*
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* @param f
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* The <code>float</code> to be printed
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* @see java.lang.Float#toString(float)
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* @throws java.io.IOException
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* If an error occurred while writing
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*/
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public abstract void print(float f) throws IOException;
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/**
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* Print a double-precision floating-point number. The string produced by
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* <code>{@link java.lang.String#valueOf(double)}</code> is written to the
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* JspWriter's buffer or, if no buffer is used, directly to the underlying
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* writer.
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*
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* @param d
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* The <code>double</code> to be printed
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* @see java.lang.Double#toString(double)
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* @throws java.io.IOException
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* If an error occurred while writing
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*/
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public abstract void print(double d) throws IOException;
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/**
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* Print an array of characters. The characters are written to the
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* JspWriter's buffer or, if no buffer is used, directly to the underlying
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* writer.
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*
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* @param s
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* The array of chars to be printed
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* @throws NullPointerException
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* If <code>s</code> is <code>null</code>
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* @throws java.io.IOException
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* If an error occurred while writing
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*/
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public abstract void print(char s[]) throws IOException;
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/**
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* Print a string. If the argument is <code>null</code> then the string
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* <code>"null"</code> is printed. Otherwise, the string's characters are
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* written to the JspWriter's buffer or, if no buffer is used, directly to
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* the underlying writer.
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*
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* @param s
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* The <code>String</code> to be printed
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* @throws java.io.IOException
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* If an error occurred while writing
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*/
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public abstract void print(String s) throws IOException;
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/**
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* Print an object. The string produced by the <code>{@link
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* java.lang.String#valueOf(Object)}</code>
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* method is written to the JspWriter's buffer or, if no buffer is used,
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* directly to the underlying writer.
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*
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* @param obj
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* The <code>Object</code> to be printed
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* @see java.lang.Object#toString()
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* @throws java.io.IOException
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* If an error occurred while writing
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*/
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public abstract void print(Object obj) throws IOException;
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/**
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* Terminate the current line by writing the line separator string. The line
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* separator string is defined by the system property
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* <code>line.separator</code>, and is not necessarily a single newline
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* character (<code>'\n'</code>).
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*
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* @throws java.io.IOException
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* If an error occurred while writing
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*/
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public abstract void println() throws IOException;
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/**
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* Print a boolean value and then terminate the line. This method behaves as
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* though it invokes <code>{@link #print(boolean)}</code> and then
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* <code>{@link #println()}</code>.
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*
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* @param x
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* the boolean to write
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* @throws java.io.IOException
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* If an error occurred while writing
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*/
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public abstract void println(boolean x) throws IOException;
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/**
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* Print a character and then terminate the line. This method behaves as
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* though it invokes <code>{@link #print(char)}</code> and then <code>{@link
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* #println()}</code>
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* .
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*
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* @param x
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* the char to write
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* @throws java.io.IOException
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* If an error occurred while writing
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*/
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public abstract void println(char x) throws IOException;
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/**
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* Print an integer and then terminate the line. This method behaves as
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* though it invokes <code>{@link #print(int)}</code> and then <code>{@link
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* #println()}</code>
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* .
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*
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* @param x
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* the int to write
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* @throws java.io.IOException
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* If an error occurred while writing
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*/
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public abstract void println(int x) throws IOException;
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/**
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* Print a long integer and then terminate the line. This method behaves as
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* though it invokes <code>{@link #print(long)}</code> and then
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* <code>{@link #println()}</code>.
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*
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* @param x
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* the long to write
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* @throws java.io.IOException
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* If an error occurred while writing
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*/
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public abstract void println(long x) throws IOException;
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/**
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* Print a floating-point number and then terminate the line. This method
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* behaves as though it invokes <code>{@link #print(float)}</code> and then
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* <code>{@link #println()}</code>.
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*
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* @param x
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* the float to write
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* @throws java.io.IOException
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* If an error occurred while writing
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*/
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public abstract void println(float x) throws IOException;
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/**
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* Print a double-precision floating-point number and then terminate the
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* line. This method behaves as though it invokes <code>{@link
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* #print(double)}</code> and
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* then <code>{@link #println()}</code>.
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*
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* @param x
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* the double to write
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* @throws java.io.IOException
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* If an error occurred while writing
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*/
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public abstract void println(double x) throws IOException;
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/**
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* Print an array of characters and then terminate the line. This method
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* behaves as though it invokes <code>print(char[])</code> and then
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* <code>println()</code>.
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*
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* @param x
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* the char[] to write
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* @throws java.io.IOException
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* If an error occurred while writing
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*/
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public abstract void println(char x[]) throws IOException;
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/**
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* Print a String and then terminate the line. This method behaves as though
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* it invokes <code>{@link #print(String)}</code> and then
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* <code>{@link #println()}</code>.
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*
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* @param x
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* the String to write
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* @throws java.io.IOException
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* If an error occurred while writing
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*/
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public abstract void println(String x) throws IOException;
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/**
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* Print an Object and then terminate the line. This method behaves as
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* though it invokes <code>{@link #print(Object)}</code> and then
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* <code>{@link #println()}</code>.
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*
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* @param x
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* the Object to write
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* @throws java.io.IOException
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* If an error occurred while writing
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*/
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public abstract void println(Object x) throws IOException;
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/**
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* Clear the contents of the buffer. If the buffer has been already been
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* flushed then the clear operation shall throw an IOException to signal the
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* fact that some data has already been irrevocably written to the client
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* response stream.
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*
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* @throws IOException
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* If an I/O error occurs
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*/
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public abstract void clear() throws IOException;
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/**
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* Clears the current contents of the buffer. Unlike clear(), this method
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* will not throw an IOException if the buffer has already been flushed. It
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* merely clears the current content of the buffer and returns.
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*
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* @throws IOException
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* If an I/O error occurs
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*/
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public abstract void clearBuffer() throws IOException;
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/**
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* Flush the stream. If the stream has saved any characters from the various
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* write() methods in a buffer, write them immediately to their intended
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* destination. Then, if that destination is another character or byte
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* stream, flush it. Thus one flush() invocation will flush all the buffers
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* in a chain of Writers and OutputStreams.
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* <p>
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* The method may be invoked indirectly if the buffer size is exceeded.
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* <p>
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* Once a stream has been closed, further write() or flush() invocations
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* will cause an IOException to be thrown.
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*
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* @exception IOException
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* If an I/O error occurs
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*/
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@Override
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public abstract void flush() throws IOException;
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/**
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* Close the stream, flushing it first.
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* <p>
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* This method needs not be invoked explicitly for the initial JspWriter as
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* the code generated by the JSP container will automatically include a call
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* to close().
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* <p>
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* Closing a previously-closed stream, unlike flush(), has no effect.
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*
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* @exception IOException
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* If an I/O error occurs
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*/
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@Override
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public abstract void close() throws IOException;
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/**
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* This method returns the size of the buffer used by the JspWriter.
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*
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* @return the size of the buffer in bytes, or 0 is unbuffered.
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*/
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public int getBufferSize() {
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return bufferSize;
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}
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/**
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* This method returns the number of unused bytes in the buffer.
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*
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* @return the number of bytes unused in the buffer
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*/
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public abstract int getRemaining();
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/**
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* This method indicates whether the JspWriter is autoFlushing.
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*
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* @return if this JspWriter is auto flushing or throwing IOExceptions on
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* buffer overflow conditions
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*/
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public boolean isAutoFlush() {
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return autoFlush;
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}
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/*
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* fields
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*/
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/**
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* The size of the buffer used by the JspWriter.
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*/
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protected int bufferSize;
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/**
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* Whether the JspWriter is autoflushing.
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*/
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protected boolean autoFlush;
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}
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