Jsp/servlet Web Learning Note daythree

JSP built-in objects

Using JSP syntax, you can access these built-in objects to perform the servlet environment interaction of JSP Web pages. Built-in objects are actually generated by a particular Java class. Each built-in object is mapped to a specific Java class or port, which is generated automatically as the server runs.

The following table lists all the JSP built-in objects:

Object Name	Describe	Scope	Classification
Appliction	Display the corresponding page is an object with an application	Entire application execution period	Scope Communication objects: retrieving servlet-related information for JSP pages
Session	All individual objects that hold personal information	Session period
PageContext	Provides an object that invokes other object methods	During page execution
Out	Represents the output data flow object that is opened by the server side to the client	During page execution	Input and Output objects: Controlling the input and output of the page
Request	The object that contains the client request information	User Request Period
Response	Contains the appropriate content objects sent from the server side to the client	Page Execution (response) period
Page	Object that displays the current page	During page execution	Servlet object: Provides information about the environment of a page
Config	JSP page initializes the received object through the container	During page execution
exception	Exception object generated when an error occurs	During page execution	Error object: Handling Errors in the page

　　

1) Scope Communication Object

Radius: pagecontext<session<appliction

A) PageContext object

Provides access to all the built-in objects defined in the scope of the current page, commonly used in the following ways:

/* Store the value of an object in PageContext as a name/value */ void SetAttribute (String name,object Value) /* gets the value of the stored object in the Pageconetxt according to the name */ void getattribute (String name)

b) Seesion Object

Used to save and track the user's session state, common methods are the same as PageContext.

c) Application Object

Acting on the entire English program, all client windows can share the object, from the beginning of the server exists, until the server shuts down, the common method is pageconext the same.

2) Input Output object a) Request object

The client request, which contains all the request information, is commonly used as follows:

/* get the data submitted by the request page based on the page form component name */ string GetParameter (string name); /* get a form component in a page request that corresponds to multiple user request data (check box, etc.) */ string Getparametervalues (string name); /* get all client-to-server parameter names */ enumeration Getparameternames ();

b) Response Object

Handling the response generated by the JSP and sending the response results to the client is commonly used as follows:

/* set the type and character encoding as the corresponding generated content */ void setContentType (String name); /* send a corresponding to the browser, indicating that it should request another URL (redirect to another URL, will lose the data, jump no longer execute the code below the Sendredirect method) */ void sendredirect (String name); /* returns the output stream object to the client */ Getoutputstream ();

c) Out Object

Represents the output stream, which is sent to the client as requested, in common methods: print (), println (), write ().

　　　　Out is rarely used in program code because the JSP expression is automatically placed in the output stream without having to explicitly point to the out output.

3) Servlet object a) Page object

Provides access to all objects defined on a Web page, representing the page itself, equivalent to the This keyword in Java .

b) Config object

The Config object stores some initial information about the servlet. The Config object represents the configuration of the servlet initialization data that compiles the JSP page.

4) Error Object exception

Handles errors in JSP pages that can be used only on the error page (pages where the page directive contains iserrorpage= "true") .

On the error page, use <%=exception.getmessage ()%> to get the error message.

Exception handling for JSP

If an exception occurs while executing the JSP Java code, you can forward the HTTP request to another specially processed Web page by using the following instruction:

<%@ page errorpage= "errorpage.jsp"%>

And in the Web page that handles the exception, the following statement should be:

<%@ page iserrorpage= "True"%> is also declared in.

In the Web page that handles the exception, you can directly access the exception implicit object for a detailed exception message.

　　

Jsp/servlet Web Learning Note daythree