Class JspWriter
- java.lang.Object
-
- java.io.Writer
-
- javax.servlet.jsp.JspWriter
-
- All Implemented Interfaces:
java.io.Closeable,java.io.Flushable,java.lang.Appendable,java.lang.AutoCloseable
- Direct Known Subclasses:
BodyContent
public abstract class JspWriter extends java.io.WriterThe 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 Description protected booleanautoFlushWhether the JspWriter is autoflushing.protected intbufferSizeThe size of the buffer used by the JspWriter.static intDEFAULT_BUFFERConstant indicating that the Writer is buffered and is using the implementation default buffer size.static intNO_BUFFERConstant indicating that the Writer is not buffering output.static intUNBOUNDED_BUFFERConstant indicating that the Writer is buffered and is unbounded; this is used in BodyContent.
-
Constructor Summary
Constructors Modifier Constructor Description protectedJspWriter(int bufferSize, boolean autoFlush)Protected constructor.
-
Method Summary
All Methods Instance Methods Abstract Methods Concrete Methods Modifier and Type Method Description abstract voidclear()Clear the contents of the buffer.abstract voidclearBuffer()Clears the current contents of the buffer.abstract voidclose()Close the stream, flushing it first.abstract voidflush()Flush the stream.intgetBufferSize()This method returns the size of the buffer used by the JspWriter.abstract intgetRemaining()This method returns the number of unused bytes in the buffer.booleanisAutoFlush()This method indicates whether the JspWriter is autoFlushing.abstract voidnewLine()Write a line separator.abstract voidprint(boolean b)Print a boolean value.abstract voidprint(char c)Print a character.abstract voidprint(char[] s)Print an array of characters.abstract voidprint(double d)Print a double-precision floating-point number.abstract voidprint(float f)Print a floating-point number.abstract voidprint(int i)Print an integer.abstract voidprint(long l)Print a long integer.abstract voidprint(java.lang.Object obj)Print an object.abstract voidprint(java.lang.String s)Print a string.abstract voidprintln()Terminate the current line by writing the line separator string.abstract voidprintln(boolean x)Print a boolean value and then terminate the line.abstract voidprintln(char x)Print a character and then terminate the line.abstract voidprintln(char[] x)Print an array of characters and then terminate the line.abstract voidprintln(double x)Print a double-precision floating-point number and then terminate the line.abstract voidprintln(float x)Print a floating-point number and then terminate the line.abstract voidprintln(int x)Print an integer and then terminate the line.abstract voidprintln(long x)Print a long integer and then terminate the line.abstract voidprintln(java.lang.Object x)Print an Object and then terminate the line.abstract voidprintln(java.lang.String x)Print a String and then terminate the line.
-
-
-
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.
-
-
Method Detail
-
newLine
public abstract void newLine() throws java.io.IOExceptionWrite a line separator. The line separator string is defined by the system propertyline.separator, and is not necessarily a single newline ('\n') character.- Throws:
java.io.IOException- If an I/O error occurs
-
print
public abstract void print(boolean b) throws java.io.IOExceptionPrint a boolean value. The string produced byis written to the JspWriter's buffer or, if no buffer is used, directly to the underlying writer.String.valueOf(boolean)- Parameters:
b- Thebooleanto be printed- Throws:
java.io.IOException- If an error occurred while writing
-
print
public abstract void print(char c) throws java.io.IOExceptionPrint a character. The character is written to the JspWriter's buffer or, if no buffer is used, directly to the underlying writer.- Parameters:
c- Thecharto be printed- Throws:
java.io.IOException- If an error occurred while writing
-
print
public abstract void print(int i) throws java.io.IOExceptionPrint an integer. The string produced byis written to the JspWriter's buffer or, if no buffer is used, directly to the underlying writer.String.valueOf(int)- Parameters:
i- Theintto be printed- Throws:
java.io.IOException- If an error occurred while writing- See Also:
Integer.toString(int)
-
print
public abstract void print(long l) throws java.io.IOExceptionPrint a long integer. The string produced byis written to the JspWriter's buffer or, if no buffer is used, directly to the underlying writer.String.valueOf(long)- Parameters:
l- Thelongto be printed- Throws:
java.io.IOException- If an error occurred while writing- See Also:
Long.toString(long)
-
print
public abstract void print(float f) throws java.io.IOExceptionPrint a floating-point number. The string produced byis written to the JspWriter's buffer or, if no buffer is used, directly to the underlying writer.String.valueOf(float)- Parameters:
f- Thefloatto be printed- Throws:
java.io.IOException- If an error occurred while writing- See Also:
Float.toString(float)
-
print
public abstract void print(double d) throws java.io.IOExceptionPrint a double-precision floating-point number. The string produced byis written to the JspWriter's buffer or, if no buffer is used, directly to the underlying writer.String.valueOf(double)- Parameters:
d- Thedoubleto be printed- Throws:
java.io.IOException- If an error occurred while writing- See Also:
Double.toString(double)
-
print
public abstract void print(char[] s) throws java.io.IOExceptionPrint 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:
java.lang.NullPointerException- Ifsisnulljava.io.IOException- If an error occurred while writing
-
print
public abstract void print(java.lang.String s) throws java.io.IOExceptionPrint a string. If the argument isnullthen 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- TheStringto be printed- Throws:
java.io.IOException- If an error occurred while writing
-
print
public abstract void print(java.lang.Object obj) throws java.io.IOExceptionPrint an object. The string produced by themethod is written to the JspWriter's buffer or, if no buffer is used, directly to the underlying writer.String.valueOf(Object)- Parameters:
obj- TheObjectto be printed- Throws:
java.io.IOException- If an error occurred while writing- See Also:
Object.toString()
-
println
public abstract void println() throws java.io.IOExceptionTerminate the current line by writing the line separator string. The line separator string is defined by the system propertyline.separator, and is not necessarily a single newline character ('\n').- Throws:
java.io.IOException- If an error occurred while writing
-
println
public abstract void println(boolean x) throws java.io.IOExceptionPrint a boolean value and then terminate the line. This method behaves as though it invokesand thenprint(boolean).println()- Parameters:
x- the boolean to write- Throws:
java.io.IOException- If an error occurred while writing
-
println
public abstract void println(char x) throws java.io.IOExceptionPrint a character and then terminate the line. This method behaves as though it invokesand thenprint(char).println()- Parameters:
x- the char to write- Throws:
java.io.IOException- If an error occurred while writing
-
println
public abstract void println(int x) throws java.io.IOExceptionPrint an integer and then terminate the line. This method behaves as though it invokesand thenprint(int).println()- Parameters:
x- the int to write- Throws:
java.io.IOException- If an error occurred while writing
-
println
public abstract void println(long x) throws java.io.IOExceptionPrint a long integer and then terminate the line. This method behaves as though it invokesand thenprint(long).println()- Parameters:
x- the long to write- Throws:
java.io.IOException- If an error occurred while writing
-
println
public abstract void println(float x) throws java.io.IOExceptionPrint a floating-point number and then terminate the line. This method behaves as though it invokesand thenprint(float).println()- Parameters:
x- the float to write- Throws:
java.io.IOException- If an error occurred while writing
-
println
public abstract void println(double x) throws java.io.IOExceptionPrint a double-precision floating-point number and then terminate the line. This method behaves as though it invokesand thenprint(double).println()- Parameters:
x- the double to write- Throws:
java.io.IOException- If an error occurred while writing
-
println
public abstract void println(char[] x) throws java.io.IOExceptionPrint an array of characters and then terminate the line. This method behaves as though it invokesprint(char[])and thenprintln().- Parameters:
x- the char[] to write- Throws:
java.io.IOException- If an error occurred while writing
-
println
public abstract void println(java.lang.String x) throws java.io.IOExceptionPrint a String and then terminate the line. This method behaves as though it invokesand thenprint(String).println()- Parameters:
x- the String to write- Throws:
java.io.IOException- If an error occurred while writing
-
println
public abstract void println(java.lang.Object x) throws java.io.IOExceptionPrint an Object and then terminate the line. This method behaves as though it invokesand thenprint(Object).println()- Parameters:
x- the Object to write- Throws:
java.io.IOException- If an error occurred while writing
-
clear
public abstract void clear() throws java.io.IOExceptionClear 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:
java.io.IOException- If an I/O error occurs
-
clearBuffer
public abstract void clearBuffer() throws java.io.IOExceptionClears 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:
java.io.IOException- If an I/O error occurs
-
flush
public abstract void flush() throws java.io.IOExceptionFlush 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:
flushin interfacejava.io.Flushable- Specified by:
flushin classjava.io.Writer- Throws:
java.io.IOException- If an I/O error occurs
-
close
public abstract void close() throws java.io.IOExceptionClose 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:
closein interfacejava.lang.AutoCloseable- Specified by:
closein interfacejava.io.Closeable- Specified by:
closein classjava.io.Writer- Throws:
java.io.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
-
-