Module jakarta.servlet.jsp
Package jakarta.servlet.jsp

Class JspWriter

java.lang.Object
java.io.Writer
jakarta.servlet.jsp.JspWriter
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:

  • Field Summary

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

    Fields inherited from class java.io.Writer

    lock

  • Constructor Summary

    Constructors
    Modifier
    Constructor
    Description
    protected
    JspWriter(int bufferSize, boolean autoFlush)
    Protected constructor.

  • Method Summary

    Modifier and Type
    Method
    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.

    Methods inherited from class java.io.Writer

    append, append, append, nullWriter, write, write, write, write, write

    Methods inherited from class java.lang.Object

    clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

  • Field Details

    • NO_BUFFER

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

    • 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:

    • 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:

    • bufferSize

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

    • autoFlush

      protected boolean autoFlush
      Whether the JspWriter is autoflushing.

  • Constructor Details

    • 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 Details

    • 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

    • print

      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

    • print

      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

    • print

      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:

    • print

      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:

    • print

      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:

    • print

      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:

    • print

      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

    • print

      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

    • print

      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:

    • 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 AutoCloseable
      Specified by:
      close in interface Closeable
      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