PageContext (Java EE 5 SDK)

javax.servlet.jsp Class PageContext

java.lang.Object
  javax.servlet.jsp.JspContext
      javax.servlet.jsp.PageContext

public abstract class PageContext

extends JspContext

PageContext extends JspContext to provide useful context information for when JSP technology is used in a Servlet environment.

A PageContext instance provides access to all the namespaces associated with a JSP page, provides access to several page attributes, as well as a layer above the implementation details. Implicit objects are added to the pageContext automatically.

The PageContext class is an abstract class, designed to be extended to provide implementation dependent implementations thereof, by conformant JSP engine runtime environments. A PageContext instance is obtained by a JSP implementation class by calling the JspFactory.getPageContext() method, and is released by calling JspFactory.releasePageContext().

An example of how PageContext, JspFactory, and other classes can be used within a JSP Page Implementation object is given elsewhere.

The PageContext provides a number of facilities to the page/component author and page implementor, including:

• a single API to manage the various scoped namespaces
• a number of convenience API's to access various public objects
• a mechanism to obtain the JspWriter for output
• a mechanism to manage session usage by the page
• a mechanism to expose page directive attributes to the scripting environment
• mechanisms to forward or include the current request to other active components in the application
• a mechanism to handle errorpage exception processing

Methods Intended for Container Generated Code

Some methods are intended to be used by the code generated by the container, not by code written by JSP page authors, or JSP tag library authors.

The methods supporting lifecycle are initialize() and release()

The following methods enable the management of nested JspWriter streams to implement Tag Extensions: pushBody()

Methods Intended for JSP authors

The following methods provide convenient access to implicit objects: getException(), getPage() getRequest(), getResponse(), getSession(), getServletConfig() and getServletContext().

The following methods provide support for forwarding, inclusion and error handling: forward(), include(), and handlePageException().

PAGE_SCOPE

public static final int PAGE_SCOPE

Page scope: (this is the default) the named reference remains available in this PageContext until the return from the current Servlet.service() invocation.

另请参见:

常量字段

REQUEST_SCOPE

public static final int REQUEST_SCOPE

Request scope: the named reference remains available from the ServletRequest associated with the Servlet until the current request is completed.

另请参见:

常量字段

SESSION_SCOPE

public static final int SESSION_SCOPE

Session scope (only valid if this page participates in a session): the named reference remains available from the HttpSession (if any) associated with the Servlet until the HttpSession is invalidated.

另请参见:

常量字段

APPLICATION_SCOPE

public static final int APPLICATION_SCOPE

Application scope: named reference remains available in the ServletContext until it is reclaimed.

另请参见:

常量字段

PAGE

public static final String PAGE

Name used to store the Servlet in this PageContext's nametables.

另请参见:

常量字段

PAGECONTEXT

public static final String PAGECONTEXT

Name used to store this PageContext in it's own name table.

另请参见:

常量字段

REQUEST

public static final String REQUEST

Name used to store ServletRequest in PageContext name table.

另请参见:

常量字段

RESPONSE

public static final String RESPONSE

Name used to store ServletResponse in PageContext name table.

另请参见:

常量字段

CONFIG

public static final String CONFIG

Name used to store ServletConfig in PageContext name table.

另请参见:

常量字段

SESSION

public static final String SESSION

Name used to store HttpSession in PageContext name table.

另请参见:

常量字段

OUT

public static final String OUT

Name used to store current JspWriter in PageContext name table.

另请参见:

常量字段

APPLICATION

public static final String APPLICATION

Name used to store ServletContext in PageContext name table.

另请参见:

常量字段

EXCEPTION

public static final String EXCEPTION

Name used to store uncaught exception in ServletRequest attribute list and PageContext name table.

另请参见:

常量字段

PageContext

public PageContext()

Sole constructor. (For invocation by subclass constructors, typically implicit.)

initialize

public abstract void initialize(Servlet servlet,
                                ServletRequest request,
                                ServletResponse response,
                                String errorPageURL,
                                boolean needsSession,
                                int bufferSize,
                                boolean autoFlush)
                         throws IOException,
                                IllegalStateException,
                                IllegalArgumentException

The initialize method is called to initialize an uninitialized PageContext so that it may be used by a JSP Implementation class to service an incoming request and response within it's _jspService() method.

This method is typically called from JspFactory.getPageContext() in order to initialize state.

This method is required to create an initial JspWriter, and associate the "out" name in page scope with this newly created object.

This method should not be used by page or tag library authors.

参数:

servlet - The Servlet that is associated with this PageContext

request - The currently pending request for this Servlet

response - The currently pending response for this Servlet

errorPageURL - The value of the errorpage attribute from the page directive or null

needsSession - The value of the session attribute from the page directive

bufferSize - The value of the buffer attribute from the page directive

autoFlush - The value of the autoflush attribute from the page directive

抛出异常:

IOException - during creation of JspWriter

IllegalStateException - if out not correctly initialized

IllegalArgumentException - If one of the given parameters is invalid

release

public abstract void release()

This method shall "reset" the internal state of a PageContext, releasing all internal references, and preparing the PageContext for potential reuse by a later invocation of initialize(). This method is typically called from JspFactory.releasePageContext().

Subclasses shall envelope this method.

This method should not be used by page or tag library authors.

getSession

public abstract HttpSession getSession()

The current value of the session object (an HttpSession).

返回:

the HttpSession for this PageContext or null

getPage

public abstract Object getPage()

The current value of the page object (In a Servlet environment, this is an instance of javax.servlet.Servlet).

返回:

the Page implementation class instance associated with this PageContext

getRequest

public abstract ServletRequest getRequest()

The current value of the request object (a ServletRequest).

返回:

The ServletRequest for this PageContext

getResponse

public abstract ServletResponse getResponse()

The current value of the response object (a ServletResponse).

返回:

the ServletResponse for this PageContext

getException

public abstract Exception getException()

The current value of the exception object (an Exception).

返回:

any exception passed to this as an errorpage

getServletConfig

public abstract ServletConfig getServletConfig()

The ServletConfig instance.

返回:

the ServletConfig for this PageContext

getServletContext

public abstract ServletContext getServletContext()

The ServletContext instance.

返回:

the ServletContext for this PageContext

forward

public abstract void forward(String relativeUrlPath)
                      throws ServletException,
                             IOException

This method is used to re-direct, or "forward" the current ServletRequest and ServletResponse to another active component in the application.

If the relativeUrlPath begins with a "/" then the URL specified is calculated relative to the DOCROOT of the ServletContext for this JSP. If the path does not begin with a "/" then the URL specified is calculated relative to the URL of the request that was mapped to the calling JSP.

It is only valid to call this method from a Thread executing within a _jspService(...) method of a JSP.

Once this method has been called successfully, it is illegal for the calling Thread to attempt to modify the ServletResponse object. Any such attempt to do so, shall result in undefined behavior. Typically, callers immediately return from _jspService(...) after calling this method.

参数:

relativeUrlPath - specifies the relative URL path to the target resource as described above

抛出异常:

IllegalStateException - if ServletResponse is not in a state where a forward can be performed

ServletException - if the page that was forwarded to throws a ServletException

IOException - if an I/O error occurred while forwarding

include

public abstract void include(String relativeUrlPath)
                      throws ServletException,
                             IOException

Causes the resource specified to be processed as part of the current ServletRequest and ServletResponse being processed by the calling Thread. The output of the target resources processing of the request is written directly to the ServletResponse output stream.

The current JspWriter "out" for this JSP is flushed as a side-effect of this call, prior to processing the include.

If the relativeUrlPath begins with a "/" then the URL specified is calculated relative to the DOCROOT of the ServletContext for this JSP. If the path does not begin with a "/" then the URL specified is calculated relative to the URL of the request that was mapped to the calling JSP.

It is only valid to call this method from a Thread executing within a _jspService(...) method of a JSP.

参数:

relativeUrlPath - specifies the relative URL path to the target resource to be included

抛出异常:

ServletException - if the page that was forwarded to throws a ServletException

IOException - if an I/O error occurred while forwarding

include

public abstract void include(String relativeUrlPath,
                             boolean flush)
                      throws ServletException,
                             IOException

Causes the resource specified to be processed as part of the current ServletRequest and ServletResponse being processed by the calling Thread. The output of the target resources processing of the request is written directly to the current JspWriter returned by a call to getOut().

If flush is true, The current JspWriter "out" for this JSP is flushed as a side-effect of this call, prior to processing the include. Otherwise, the JspWriter "out" is not flushed.

If the relativeUrlPath begins with a "/" then the URL specified is calculated relative to the DOCROOT of the ServletContext for this JSP. If the path does not begin with a "/" then the URL specified is calculated relative to the URL of the request that was mapped to the calling JSP.

It is only valid to call this method from a Thread executing within a _jspService(...) method of a JSP.

参数:

relativeUrlPath - specifies the relative URL path to the target resource to be included

flush - True if the JspWriter is to be flushed before the include, or false if not.

抛出异常:

ServletException - if the page that was forwarded to throws a ServletException

IOException - if an I/O error occurred while forwarding

从以下版本开始:

JSP 2.0

handlePageException

public abstract void handlePageException(Exception e)
                                  throws ServletException,
                                         IOException

This method is intended to process an unhandled 'page' level exception by forwarding the exception to the specified error page for this JSP. If forwarding is not possible (for example because the response has already been committed), an implementation dependent mechanism should be used to invoke the error page (e.g. "including" the error page instead).

If no error page is defined in the page, the exception should be rethrown so that the standard servlet error handling takes over.

A JSP implementation class shall typically clean up any local state prior to invoking this and will return immediately thereafter. It is illegal to generate any output to the client, or to modify any ServletResponse state after invoking this call.

This method is kept for backwards compatiblity reasons. Newly generated code should use PageContext.handlePageException(Throwable).

参数:

e - the exception to be handled

抛出异常:

ServletException - if an error occurs while invoking the error page

IOException - if an I/O error occurred while invoking the error page

NullPointerException - if the exception is null

另请参见:

handlePageException(Throwable)

handlePageException

public abstract void handlePageException(Throwable t)
                                  throws ServletException,
                                         IOException

This method is intended to process an unhandled 'page' level exception by forwarding the exception to the specified error page for this JSP. If forwarding is not possible (for example because the response has already been committed), an implementation dependent mechanism should be used to invoke the error page (e.g. "including" the error page instead).

If no error page is defined in the page, the exception should be rethrown so that the standard servlet error handling takes over.

This method is intended to process an unhandled "page" level exception by redirecting the exception to either the specified error page for this JSP, or if none was specified, to perform some implementation dependent action.

A JSP implementation class shall typically clean up any local state prior to invoking this and will return immediately thereafter. It is illegal to generate any output to the client, or to modify any ServletResponse state after invoking this call.

参数:

t - the throwable to be handled

抛出异常:

ServletException - if an error occurs while invoking the error page

IOException - if an I/O error occurred while invoking the error page

NullPointerException - if the exception is null

另请参见:

handlePageException(Exception)

pushBody

public BodyContent pushBody()

Return a new BodyContent object, save the current "out" JspWriter, and update the value of the "out" attribute in the page scope attribute namespace of the PageContext.

返回:

the new BodyContent

getErrorData

public ErrorData getErrorData()

Provides convenient access to error information.

返回:

an ErrorData instance containing information about the error, as obtained from the request attributes, as per the Servlet specification. If this is not an error page (that is, if the isErrorPage attribute of the page directive is not set to "true"), the information is meaningless.

从以下版本开始:

JSP 2.0

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