Java Server Pages: A Code-Intensive Premium Reference- P22

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Java Server Pages: A Code-Intensive Premium Reference- P22:Before you begin reading Pure JSP Java Server Pages, you might want to take a look at its basic structure. This should help you outline your reading plan if you choose not to read the text from cover to cover. This introduction gives you an overview of what each chapter covers.

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Nội dung Text: Java Server Pages: A Code-Intensive Premium Reference- P22

Classes Classes for the javax.servlet package are GenericServlet, ServletInputStream, and ServletOutputStream. Their methods are described in the following sections. GenericServlet Class The GenericServlet class was created to provide a basic foundation of new servlets. It provides default life cycle methods and default implementations of the ServletConfig's methods. GenericServlet() Method public GenericServlet() The GenericServlet() method is an empty default constructor. GenericServlet() has no parameters, returns no value, and throws no exceptions. destroy() Method public void destroy() The destroy() method is executed when the servlet is removed from the running service. It performs any cleanup of resources that were allocated in the init() method. destroy() has no parameters, returns no value, and throws no exceptions. getInitParameter() Method public java.lang.String getInitParameter( java.lang.String name) The getInitParameter() method returns a String containing the value of the initialization parameter keyed by the passed in name. getInitParameter() throws no exceptions. Parameters java.lang.String Returns java.lang.String getInitParameterNames() Method public java.util.Enumeration getInitParameterNames() The getInitParameterNames() method returns an Enumeration containing all of the names for each initialization parameter. getInitParameterNames() has no parameters and throws no exceptions. Returns java.util.Enumeration getServletConfig() Method public ServletConfig getServletConfig() The getServletConfig() method returns a ServletConfig object containing any startup configuration information for this servlet. getServletConfig() has no parameters and throws no exceptions. Returns ServletConfig getServletContext() Method public ServletContext getServletContext() The getServletContext() method returns a ServletContext object containing information about the servlet's network service. getServletContext() has no parameters and throws no exceptions. Returns ServletContext - 211 -
getServletInfo() Method public java.lang.String getServletInfo() The getServletInfo() method returns a String containing servlet-specific information about the implementing servlet. getServletInfo() has no parameters and throws no exceptions. Returns java.lang.String init(ServletConfig config) Method public void init(ServletConfig config) throws ServletException The init() method marks the beginning of a servlet's life. It is called only when the servlet is first loaded, and it must execute successfully before the servlet can service requests. The init() method should contain all initialization code for the servlet. It returns no value. Parameters ServletConfig (encapsulates the servlet's startup configuration and initialization parameters) Exceptions Thrown ServletException init() Method public void init() throws ServletException This parameterless implementation of the init() method is provided only for convenience. It prevents a derived servlet from having to store the ServletConfig object. init() has no parameters and returns no value. Exceptions Thrown ServletException log(java.lang.String message) Method public void log(java.lang.String message) The log() method takes the passed in message and the name of the servlet and writes them to a log file. The location of the log is server specific. log() returns no value and throws no exceptions. Parameters java.lang.String log(java.lang.String message, java.lang.Throwable t) Method public void log(java.lang.String message, java.lang.Throwable t) This log() method takes the passed in message and Throwable object and logs the message with a stack trace from the Throwable object. log() returns no value and throws no exceptions. Parameters java.lang.String java.lang.Throwable service() Method public void service(ServletRequest request, ServletResponse response) throws ServletException, java.io.IOException - 212 -
The service() method defines the servlet's entry point for servicing requests. It can be executed only after the servlet's init() method has executed successfully. The service() method is the life cycle method executed for every incoming request. It returns no value. Parameters ServletRequest ServletResponse Exceptions Thrown ServletException java.io.IOException ServletInputStream Class The ServletInputStream is an abstract class defined for servlet writers to get data from the client. It is meant to be implemented by a network services writer. This class has two methods. ServletInputStream() Method protected ServletInputStream() The ServletInputStream() method is the empty default constructor. It has no parameters, returns no value, and throws no exceptions. readLine() Method public void readLine(byte[] b, int off, int len) throws java.io.IOException The readLine() method reads the len of bytes into the passed in byte array b, starting at position off. If the character '\n' is encountered, then no more bytes are read in. readLine() returns no value. Parameters byte[] int int Exceptions Thrown java.io.IOException ServletOutputStream Class The ServletOutputStream class is used to write responses back to the client. It is an abstract class that is implemented by the network services implementor. To access the ServletOutputStream, you must call the ServletResponse's getOutputStream() method. The class has several methods. ServletOutputStream() Method public ServletOutputStream() throws java.io.IOException The ServletOutputStream() method is the empty default constructor. It has no parameters and returns no value. Exceptions Thrown java.io.IOException print(boolean value) Method public void print(boolean value) throws java.io.IOException This version of the print() method prints the passed in boolean value to the output stream. - 213 -
Parameters boolean Note The print() method always throws a java.io.IOException exception. For all print values, the print() method returns no value. print(char value) Method public void print(char value) throws java.io.IOException This version of the print() method prints the passed in char value to the output stream. Parameters char print(double value) Method public void print(double value) throws java.io.IOException This version of the print() method prints the passed in double value to the output stream. Parameters double print(float value) Method public void print(float value) throws java.io.IOException This version of the print() method prints the passed in float value to the output stream. Parameters float print(int value) Method public void print(int value) throws java.io.IOException This version of the print() method prints the passed in int value to the output stream. Parameters int print(long value) Method public void print(long value) throws java.io.IOException This version of the print() method prints the passed in long value to the output stream. Parameters long print(java.lang.String value) Method public void print(java.lang.String value) throws java.io.IOException This version of the print() method prints the passed in String value to the output stream. Parameters java.lang.String - 214 -
println() Method public void println() throws java.io.IOException This version of the println() method prints CRLF to the output stream and has no parameters. Note The println() method always throws a java.io.IOException exception. For all print values, the println() method returns no value. println(java.lang.String value) Method public void println(java.lang.String value) throws java.io.IOException This version of the println() method prints the passed in String value to the output stream, followed by a CRLF. Parameters java.lang.String println(boolean value) Method public void println(boolean value) throws java.io.IOException This version of the println() method prints the passed in boolean value to the output stream, followed by a CRLF. Parameters boolean println(char value) Method public void println(char value) throws java.io.IOException This version of the println() method prints the passed in char value to the output stream, followed by a CRLF. Parameters char println(int value) Method public void println(int value) throws java.io.IOException This version of the println() method prints the passed in int value to the output stream, followed by a CRLF. Parameters int println(long value) Method public void println(long value) throws java.io.IOException This version of the println() method prints the passed in long value to the output stream, followed by a CRLF. Parameters long println(float value) Method public void println(float value) - 215 -
throws java.io.IOException This version of the println() method prints the passed in float value to the output stream, followed by a CRLF. Parameters float println(double value) Method public void println(double value) throws java.io.IOException This version of the println() method prints the passed in double value to the output stream, followed by a CRLF. Parameters double Classes Classes for the javax.servlet package are GenericServlet, ServletInputStream, and ServletOutputStream. Their methods are described in the following sections. GenericServlet Class The GenericServlet class was created to provide a basic foundation of new servlets. It provides default life cycle methods and default implementations of the ServletConfig's methods. GenericServlet() Method public GenericServlet() The GenericServlet() method is an empty default constructor. GenericServlet() has no parameters, returns no value, and throws no exceptions. destroy() Method public void destroy() The destroy() method is executed when the servlet is removed from the running service. It performs any cleanup of resources that were allocated in the init() method. destroy() has no parameters, returns no value, and throws no exceptions. getInitParameter() Method public java.lang.String getInitParameter( java.lang.String name) The getInitParameter() method returns a String containing the value of the initialization parameter keyed by the passed in name. getInitParameter() throws no exceptions. Parameters java.lang.String Returns java.lang.String getInitParameterNames() Method public java.util.Enumeration getInitParameterNames() The getInitParameterNames() method returns an Enumeration containing all of the names for each initialization parameter. getInitParameterNames() has no parameters and throws no exceptions. Returns java.util.Enumeration - 216 -
getServletConfig() Method public ServletConfig getServletConfig() The getServletConfig() method returns a ServletConfig object containing any startup configuration information for this servlet. getServletConfig() has no parameters and throws no exceptions. Returns ServletConfig getServletContext() Method public ServletContext getServletContext() The getServletContext() method returns a ServletContext object containing information about the servlet's network service. getServletContext() has no parameters and throws no exceptions. Returns ServletContext getServletInfo() Method public java.lang.String getServletInfo() The getServletInfo() method returns a String containing servlet-specific information about the implementing servlet. getServletInfo() has no parameters and throws no exceptions. Returns java.lang.String init(ServletConfig config) Method public void init(ServletConfig config) throws ServletException The init() method marks the beginning of a servlet's life. It is called only when the servlet is first loaded, and it must execute successfully before the servlet can service requests. The init() method should contain all initialization code for the servlet. It returns no value. Parameters ServletConfig (encapsulates the servlet's startup configuration and initialization parameters) Exceptions Thrown ServletException init() Method public void init() throws ServletException This parameterless implementation of the init() method is provided only for convenience. It prevents a derived servlet from having to store the ServletConfig object. init() has no parameters and returns no value. Exceptions Thrown ServletException log(java.lang.String message) Method public void log(java.lang.String message) The log() method takes the passed in message and the name of the servlet and writes them to a log file. The location of the log is server specific. log() returns no value and throws no exceptions. Parameters java.lang.String - 217 -
log(java.lang.String message, java.lang.Throwable t) Method public void log(java.lang.String message, java.lang.Throwable t) This log() method takes the passed in message and Throwable object and logs the message with a stack trace from the Throwable object. log() returns no value and throws no exceptions. Parameters java.lang.String java.lang.Throwable service() Method public void service(ServletRequest request, ServletResponse response) throws ServletException, java.io.IOException The service() method defines the servlet's entry point for servicing requests. It can be executed only after the servlet's init() method has executed successfully. The service() method is the life cycle method executed for every incoming request. It returns no value. Parameters ServletRequest ServletResponse Exceptions Thrown ServletException java.io.IOException ServletInputStream Class The ServletInputStream is an abstract class defined for servlet writers to get data from the client. It is meant to be implemented by a network services writer. This class has two methods. ServletInputStream() Method protected ServletInputStream() The ServletInputStream() method is the empty default constructor. It has no parameters, returns no value, and throws no exceptions. readLine() Method public void readLine(byte[] b, int off, int len) throws java.io.IOException The readLine() method reads the len of bytes into the passed in byte array b, starting at position off. If the character '\n' is encountered, then no more bytes are read in. readLine() returns no value. Parameters byte[] int int Exceptions Thrown java.io.IOException - 218 -
ServletOutputStream Class The ServletOutputStream class is used to write responses back to the client. It is an abstract class that is implemented by the network services implementor. To access the ServletOutputStream, you must call the ServletResponse's getOutputStream() method. The class has several methods. ServletOutputStream() Method public ServletOutputStream() throws java.io.IOException The ServletOutputStream() method is the empty default constructor. It has no parameters and returns no value. Exceptions Thrown java.io.IOException print(boolean value) Method public void print(boolean value) throws java.io.IOException This version of the print() method prints the passed in boolean value to the output stream. Parameters boolean Note The print() method always throws a java.io.IOException exception. For all print values, the print() method returns no value. print(char value) Method public void print(char value) throws java.io.IOException This version of the print() method prints the passed in char value to the output stream. Parameters char print(double value) Method public void print(double value) throws java.io.IOException This version of the print() method prints the passed in double value to the output stream. Parameters double print(float value) Method public void print(float value) throws java.io.IOException This version of the print() method prints the passed in float value to the output stream. Parameters float print(int value) Method public void print(int value) throws java.io.IOException This version of the print() method prints the passed in int value to the output stream. Parameters int - 219 -
print(long value) Method public void print(long value) throws java.io.IOException This version of the print() method prints the passed in long value to the output stream. Parameters long print(java.lang.String value) Method public void print(java.lang.String value) throws java.io.IOException This version of the print() method prints the passed in String value to the output stream. Parameters java.lang.String println() Method public void println() throws java.io.IOException This version of the println() method prints CRLF to the output stream and has no parameters. Note The println() method always throws a java.io.IOException exception. For all print values, the println() method returns no value. println(java.lang.String value) Method public void println(java.lang.String value) throws java.io.IOException This version of the println() method prints the passed in String value to the output stream, followed by a CRLF. Parameters java.lang.String println(boolean value) Method public void println(boolean value) throws java.io.IOException This version of the println() method prints the passed in boolean value to the output stream, followed by a CRLF. Parameters boolean println(char value) Method public void println(char value) throws java.io.IOException This version of the println() method prints the passed in char value to the output stream, followed by a CRLF. Parameters char println(int value) Method public void println(int value) throws java.io.IOException - 220 -