javax.servlet.jsp

Class JspWriter

Inhaltsverzeichnis
  • All Implemented Interfaces:
    Closeable, Flushable, Appendable, AutoCloseable
    Direct Known Subclasses:
    BodyContent

    public abstract class JspWriter
extends Writer

    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:

    • Exceeding the buffer is not a fatal error; when the buffer is exceeded, just flush the output.
    • Exceeding the buffer is a fatal error; when the buffer is exceeded, raise an exception.

    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 Also:
    Writer, BufferedWriter, PrintWriter

    • Field Summary

      Fields 
      Modifier and Type Field and Description
      protected boolean autoFlush
      Whether the JspWriter is autoflushing.
      protected int bufferSize
      The size of the buffer used by the JspWriter.
      static int DEFAULT_BUFFER
      Constant indicating that the Writer is buffered and is using the implementation default buffer size.
      static int NO_BUFFER
      Constant indicating that the Writer is not buffering output.
      static int UNBOUNDED_BUFFER
      Constant indicating that the Writer is buffered and is unbounded; this is used in BodyContent.

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      • Fields inherited from class java.io.Writer

        lock

    • Method Summary

      All Methods Instance Methods Abstract Methods Concrete Methods 
      Modifier and Type Method and Description
      abstract void clear()
      Clear the contents of the buffer.
      abstract void clearBuffer()
      Clears the current contents of the buffer.
      abstract void close()
      Close the stream, flushing it first.
      abstract void flush()
      Flush the stream.
      int getBufferSize()
      This method returns the size of the buffer used by the JspWriter.
      abstract int getRemaining()
      This method returns the number of unused bytes in the buffer.
      boolean isAutoFlush()
      This method indicates whether the JspWriter is autoFlushing.
      abstract void newLine()
      Write a line separator.
      abstract void print(boolean b)
      Print a boolean value.
      abstract void print(char c)
      Print a character.
      abstract void print(char[] s)
      Print an array of characters.
      abstract void print(double d)
      Print a double-precision floating-point number.
      abstract void print(float f)
      Print a floating-point number.
      abstract void print(int i)
      Print an integer.
      abstract void print(long l)
      Print a long integer.
      abstract void print(Object obj)
      Print an object.
      abstract void print(String s)
      Print a string.
      abstract void println()
      Terminate the current line by writing the line separator string.
      abstract void println(boolean x)
      Print a boolean value and then terminate the line.
      abstract void println(char x)
      Print a character and then terminate the line.
      abstract void println(char[] x)
      Print an array of characters and then terminate the line.
      abstract void println(double x)
      Print a double-precision floating-point number and then terminate the line.
      abstract void println(float x)
      Print a floating-point number and then terminate the line.
      abstract void println(int x)
      Print an integer and then terminate the line.
      abstract void println(long x)
      Print a long integer and then terminate the line.
      abstract void println(Object x)
      Print an Object and then terminate the line.
      abstract void println(String x)
      Print a String and then terminate the line.

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    • Field Detail

      • NO_BUFFER

        public static final int NO_BUFFER
        Constant indicating that the Writer is not buffering output.
        See Also:
        Constant Field Values

      • DEFAULT_BUFFER

        public static final int DEFAULT_BUFFER
        Constant indicating that the Writer is buffered and is using the implementation default buffer size.
        See Also:
        Constant Field Values

      • UNBOUNDED_BUFFER

        public static final int UNBOUNDED_BUFFER
        Constant indicating that the Writer is buffered and is unbounded; this is used in BodyContent.
        See Also:
        Constant Field Values

      • bufferSize

        protected int bufferSize
        The size of the buffer used by the JspWriter.

      • autoFlush

        protected boolean autoFlush
        Whether the JspWriter is autoflushing.

    • Constructor Detail

      • JspWriter

        protected JspWriter(int bufferSize,
                    boolean autoFlush)
        Protected constructor.
        Parameters:
        bufferSize - the size of the buffer to be used by the JspWriter
        autoFlush - whether the JspWriter should be autoflushing

    • Method Detail

      • newLine

        public abstract void newLine()
                      throws IOException
        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.
        Throws:
        IOException - If an I/O error occurs
      • public abstract void print(boolean b)
                    throws IOException
        Print a boolean value. The string produced by String.valueOf(boolean) is written to the JspWriter's buffer or, if no buffer is used, directly to the underlying writer.
        Parameters:
        b - The boolean to be printed
        Throws:
        IOException - If an error occured while writing
      • public abstract void print(char c)
                    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.
        Parameters:
        c - The char to be printed
        Throws:
        IOException - If an error occured while writing
      • public abstract void print(int i)
                    throws IOException
        Print an integer. The string produced by String.valueOf(int) is written to the JspWriter's buffer or, if no buffer is used, directly to the underlying writer.
        Parameters:
        i - The int to be printed
        Throws:
        IOException - If an error occured while writing
        See Also:
        Integer.toString(int)
      • public abstract void print(long l)
                    throws IOException
        Print a long integer. The string produced by String.valueOf(long) is written to the JspWriter's buffer or, if no buffer is used, directly to the underlying writer.
        Parameters:
        l - The long to be printed
        Throws:
        IOException - If an error occured while writing
        See Also:
        Long.toString(long)
      • public abstract void print(float f)
                    throws IOException
        Print a floating-point number. The string produced by String.valueOf(float) is written to the JspWriter's buffer or, if no buffer is used, directly to the underlying writer.
        Parameters:
        f - The float to be printed
        Throws:
        IOException - If an error occured while writing
        See Also:
        Float.toString(float)
      • public abstract void print(double d)
                    throws IOException
        Print a double-precision floating-point number. The string produced by String.valueOf(double) is written to the JspWriter's buffer or, if no buffer is used, directly to the underlying writer.
        Parameters:
        d - The double to be printed
        Throws:
        IOException - If an error occured while writing
        See Also:
        Double.toString(double)
      • public abstract void print(char[] s)
                    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.
        Parameters:
        s - The array of chars to be printed
        Throws:
        NullPointerException - If s is null
        IOException - If an error occured while writing
      • public abstract void print(String 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.
        Parameters:
        s - The String to be printed
        Throws:
        IOException - If an error occured while writing
      • public abstract void print(Object obj)
                    throws IOException
        Print an object. The string produced by the String.valueOf(Object) method is written to the JspWriter's buffer or, if no buffer is used, directly to the underlying writer.
        Parameters:
        obj - The Object to be printed
        Throws:
        IOException - If an error occured while writing
        See Also:
        Object.toString()

      • println

        public abstract void println()
                      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:
        IOException - If an error occured while writing

      • println

        public abstract void println(boolean x)
                      throws IOException
        Print a boolean value and then terminate the line. This method behaves as though it invokes print(boolean) and then println().
        Parameters:
        x - the boolean to write
        Throws:
        IOException - If an error occured while writing

      • println

        public abstract void println(char x)
                      throws IOException
        Print a character and then terminate the line. This method behaves as though it invokes print(char) and then println().
        Parameters:
        x - the char to write
        Throws:
        IOException - If an error occured while writing

      • println

        public abstract void println(int x)
                      throws IOException
        Print an integer and then terminate the line. This method behaves as though it invokes print(int) and then println().
        Parameters:
        x - the int to write
        Throws:
        IOException - If an error occured while writing

      • println

        public abstract void println(long x)
                      throws IOException
        Print a long integer and then terminate the line. This method behaves as though it invokes print(long) and then println().
        Parameters:
        x - the long to write
        Throws:
        IOException - If an error occured while writing

      • println

        public abstract void println(float x)
                      throws IOException
        Print a floating-point number and then terminate the line. This method behaves as though it invokes print(float) and then println().
        Parameters:
        x - the float to write
        Throws:
        IOException - If an error occured while writing

      • println

        public abstract void println(double x)
                      throws IOException
        Print a double-precision floating-point number and then terminate the line. This method behaves as though it invokes print(double) and then println().
        Parameters:
        x - the double to write
        Throws:
        IOException - If an error occured while writing

      • println

        public abstract void println(char[] 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().
        Parameters:
        x - the char[] to write
        Throws:
        IOException - If an error occured while writing

      • println

        public abstract void println(String x)
                      throws IOException
        Print a String and then terminate the line. This method behaves as though it invokes print(String) and then println().
        Parameters:
        x - the String to write
        Throws:
        IOException - If an error occured while writing

      • println

        public abstract void println(Object x)
                      throws IOException
        Print an Object and then terminate the line. This method behaves as though it invokes print(Object) and then println().
        Parameters:
        x - the Object to write
        Throws:
        IOException - If an error occured while writing

      • clear

        public abstract void clear()
                    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

      • clearBuffer

        public abstract void clearBuffer()
                          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

      • flush

        public abstract void flush()
                    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.

        Specified by:
        flush in interface Flushable
        Specified by:
        flush in class Writer
        Throws:
        IOException - If an I/O error occurs

      • close

        public abstract void close()
                    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.

        Specified by:
        close in interface Closeable
        Specified by:
        close in interface AutoCloseable
        Specified by:
        close in class Writer
        Throws:
        IOException - If an I/O error occurs

      • getBufferSize

        public int getBufferSize()
        This method returns the size of the buffer used by the JspWriter.
        Returns:
        the size of the buffer in bytes, or 0 is unbuffered.

      • getRemaining

        public abstract int getRemaining()
        This method returns the number of unused bytes in the buffer.
        Returns:
        the number of bytes unused in the buffer

      • isAutoFlush

        public boolean isAutoFlush()
        This method indicates whether the JspWriter is autoFlushing.
        Returns:
        if this JspWriter is auto flushing or throwing IOExceptions on buffer overflow conditions

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Dokument erstellt 11/06/2005, zuletzt geändert 18/08/2025
Quelle des gedruckten Dokuments:https://www.gaudry.be/de/java-api-javaee-rf-javax/servlet/jsp/jspwriter.html

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