* 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 java.io.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: *
* 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
*/
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 line.separator, 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 {@link
* java.lang.String#valueOf(boolean)} is written to the
* JspWriter's buffer or, if no buffer is used, directly to the
* underlying writer.
*
* @param b The boolean 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 char 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 {@link
* java.lang.String#valueOf(int)} is written to the
* JspWriter's buffer or, if no buffer is used, directly to the
* underlying writer.
*
* @param i The int 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 {@link
* java.lang.String#valueOf(long)} is written to the
* JspWriter's buffer or, if no buffer is used, directly to the
* underlying writer.
*
* @param l The long 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 {@link
* java.lang.String#valueOf(float)} is written to the
* JspWriter's buffer or, if no buffer is used, directly to the
* underlying writer.
*
* @param f The float 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
* {@link java.lang.String#valueOf(double)} is written to
* the JspWriter's buffer or, if no buffer is used, directly to the
* underlying writer.
*
* @param d The double 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 s is null
* @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 null then the string
* "null" 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 String 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 {@link
* java.lang.String#valueOf(Object)} method is written to the
* JspWriter's buffer or, if no buffer is used, directly to the
* underlying writer.
*
* @param obj The Object 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
* line.separator, and is not necessarily a single newline
* character ('\n').
* @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 {@link #print(boolean)} and then
* {@link #println()}.
*
* @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 {@link #print(char)} and then {@link
* #println()}.
*
* @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 {@link #print(int)} and then {@link
* #println()}.
*
* @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 {@link #print(long)} and then
* {@link #println()}.
*
* @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 {@link #print(float)} and then
* {@link #println()}.
*
* @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 {@link
* #print(double)} and then {@link #println()}.
*
* @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 print(char[]) and then
* println().
*
* @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 {@link #print(String)} and then
* {@link #println()}.
*
* @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 {@link #print(Object)} and then
* {@link #println()}.
*
* @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.
*
* 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 */ abstract public 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 */ 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; }