Java Doc for HttpServlet.java in  » Sevlet-Container » apache-tomcat-6.0.14 » javax » servlet » http » Java Source Code / Java DocumentationJava Source Code and Java Documentation

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Java Source Code / Java Documentation » Sevlet Container » apache tomcat 6.0.14 » javax.servlet.http 
Source Cross Reference  Class Diagram Java Document (Java Doc) 


java.lang.Object
   javax.servlet.GenericServlet
      javax.servlet.http.HttpServlet

All known Subclasses:   org.apache.jasper.servlet.JspServlet,  org.apache.catalina.manager.ManagerServlet,  org.apache.catalina.servlets.InvokerServlet,  org.apache.catalina.manager.JMXProxyServlet,  org.apache.catalina.ssi.SSIServlet,  org.apache.jasper.runtime.HttpJspBase,  org.apache.catalina.servlets.DefaultServlet,  org.apache.catalina.manager.StatusManagerServlet,  org.apache.catalina.manager.host.HostManagerServlet,  org.apache.catalina.servlets.CGIServlet,
HttpServlet
abstract public class HttpServlet extends GenericServlet implements java.io.Serializable(Code)
Provides an abstract class to be subclassed to create an HTTP servlet suitable for a Web site. A subclass of HttpServlet must override at least one method, usually one of these:
  • doGet, if the servlet supports HTTP GET requests
  • doPost, for HTTP POST requests
  • doPut, for HTTP PUT requests
  • doDelete, for HTTP DELETE requests
  • init and destroy, to manage resources that are held for the life of the servlet
  • getServletInfo, which the servlet uses to provide information about itself

There's almost no reason to override the service method. service handles standard HTTP requests by dispatching them to the handler methods for each HTTP request type (the doXXX methods listed above).

Likewise, there's almost no reason to override the doOptions and doTrace methods.

Servlets typically run on multithreaded servers, so be aware that a servlet must handle concurrent requests and be careful to synchronize access to shared resources. Shared resources include in-memory data such as instance or class variables and external objects such as files, database connections, and network connections. See the Java Tutorial on Multithreaded Programming for more information on handling multiple threads in a Java program.
author:
   Various
version:
   $Version$




Constructor Summary
public  HttpServlet()
     Does nothing, because this is an abstract class.

Method Summary
protected  voiddoDelete(HttpServletRequest req, HttpServletResponse resp)
     Called by the server (via the service method) to allow a servlet to handle a DELETE request. The DELETE operation allows a client to remove a document or Web page from the server.

This method does not need to be either safe or idempotent.

protected  voiddoGet(HttpServletRequest req, HttpServletResponse resp)
     Called by the server (via the service method) to allow a servlet to handle a GET request.
protected  voiddoHead(HttpServletRequest req, HttpServletResponse resp)
    

Receives an HTTP HEAD request from the protected service method and handles the request. The client sends a HEAD request when it wants to see only the headers of a response, such as Content-Type or Content-Length.

protected  voiddoOptions(HttpServletRequest req, HttpServletResponse resp)
     Called by the server (via the service method) to allow a servlet to handle a OPTIONS request. The OPTIONS request determines which HTTP methods the server supports and returns an appropriate header.
protected  voiddoPost(HttpServletRequest req, HttpServletResponse resp)
     Called by the server (via the service method) to allow a servlet to handle a POST request. The HTTP POST method allows the client to send data of unlimited length to the Web server a single time and is useful when posting information such as credit card numbers.

When overriding this method, read the request data, write the response headers, get the response's writer or output stream object, and finally, write the response data.

protected  voiddoPut(HttpServletRequest req, HttpServletResponse resp)
     Called by the server (via the service method) to allow a servlet to handle a PUT request. The PUT operation allows a client to place a file on the server and is similar to sending a file by FTP.

When overriding this method, leave intact any content headers sent with the request (including Content-Length, Content-Type, Content-Transfer-Encoding, Content-Encoding, Content-Base, Content-Language, Content-Location, Content-MD5, and Content-Range).

protected  voiddoTrace(HttpServletRequest req, HttpServletResponse resp)
     Called by the server (via the service method) to allow a servlet to handle a TRACE request. A TRACE returns the headers sent with the TRACE request to the client, so that they can be used in debugging.
protected  longgetLastModified(HttpServletRequest req)
     Returns the time the HttpServletRequest object was last modified, in milliseconds since midnight January 1, 1970 GMT.
protected  voidservice(HttpServletRequest req, HttpServletResponse resp)
     Receives standard HTTP requests from the public service method and dispatches them to the doXXX methods defined in this class.
public  voidservice(ServletRequest req, ServletResponse res)
     Dispatches client requests to the protected service method.


Constructor Detail
HttpServlet
public HttpServlet()(Code)
Does nothing, because this is an abstract class.




Method Detail
doDelete
protected void doDelete(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException(Code)
Called by the server (via the service method) to allow a servlet to handle a DELETE request. The DELETE operation allows a client to remove a document or Web page from the server.

This method does not need to be either safe or idempotent. Operations requested through DELETE can have side effects for which users can be held accountable. When using this method, it may be useful to save a copy of the affected URL in temporary storage.

If the HTTP DELETE request is incorrectly formatted, doDelete returns an HTTP "Bad Request" message.
Parameters:
  req - the HttpServletRequest object thatcontains the request the client made ofthe servlet
Parameters:
  resp - the HttpServletResponse object thatcontains the response the servlet returnsto the client
exception:
  IOException - if an input or output error occurswhile the servlet is handling theDELETE request
exception:
  ServletException - if the request for theDELETE cannot be handled




doGet
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException(Code)
Called by the server (via the service method) to allow a servlet to handle a GET request.

Overriding this method to support a GET request also automatically supports an HTTP HEAD request. A HEAD request is a GET request that returns no body in the response, only the request header fields.

When overriding this method, read the request data, write the response headers, get the response's writer or output stream object, and finally, write the response data. It's best to include content type and encoding. When using a PrintWriter object to return the response, set the content type before accessing the PrintWriter object.

The servlet container must write the headers before committing the response, because in HTTP the headers must be sent before the response body.

Where possible, set the Content-Length header (with the javax.servlet.ServletResponse.setContentLength method), to allow the servlet container to use a persistent connection to return its response to the client, improving performance. The content length is automatically set if the entire response fits inside the response buffer.

When using HTTP 1.1 chunked encoding (which means that the response has a Transfer-Encoding header), do not set the Content-Length header.

The GET method should be safe, that is, without any side effects for which users are held responsible. For example, most form queries have no side effects. If a client request is intended to change stored data, the request should use some other HTTP method.

The GET method should also be idempotent, meaning that it can be safely repeated. Sometimes making a method safe also makes it idempotent. For example, repeating queries is both safe and idempotent, but buying a product online or modifying data is neither safe nor idempotent.

If the request is incorrectly formatted, doGet returns an HTTP "Bad Request" message.
Parameters:
  req - an HttpServletRequest object thatcontains the request the client has madeof the servlet
Parameters:
  resp - an HttpServletResponse object thatcontains the response the servlet sendsto the client
exception:
  IOException - if an input or output error is detected when the servlet handlesthe GET request
exception:
  ServletException - if the request for the GETcould not be handled
See Also:   javax.servlet.ServletResponse.setContentType




doHead
protected void doHead(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException(Code)

Receives an HTTP HEAD request from the protected service method and handles the request. The client sends a HEAD request when it wants to see only the headers of a response, such as Content-Type or Content-Length. The HTTP HEAD method counts the output bytes in the response to set the Content-Length header accurately.

If you override this method, you can avoid computing the response body and just set the response headers directly to improve performance. Make sure that the doHead method you write is both safe and idempotent (that is, protects itself from being called multiple times for one HTTP HEAD request).

If the HTTP HEAD request is incorrectly formatted, doHead returns an HTTP "Bad Request" message.
Parameters:
  req - the request object that is passedto the servlet
Parameters:
  resp - the response object that the servletuses to return the headers to the clien
exception:
  IOException - if an input or output error occurs
exception:
  ServletException - if the request for the HEADcould not be handled




doOptions
protected void doOptions(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException(Code)
Called by the server (via the service method) to allow a servlet to handle a OPTIONS request. The OPTIONS request determines which HTTP methods the server supports and returns an appropriate header. For example, if a servlet overrides doGet, this method returns the following header:

Allow: GET, HEAD, TRACE, OPTIONS

There's no need to override this method unless the servlet implements new HTTP methods, beyond those implemented by HTTP 1.1.
Parameters:
  req - the HttpServletRequest object thatcontains the request the client made ofthe servlet
Parameters:
  resp - the HttpServletResponse object thatcontains the response the servlet returnsto the client
exception:
  IOException - if an input or output error occurswhile the servlet is handling theOPTIONS request
exception:
  ServletException - if the request for theOPTIONS cannot be handled




doPost
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException(Code)
Called by the server (via the service method) to allow a servlet to handle a POST request. The HTTP POST method allows the client to send data of unlimited length to the Web server a single time and is useful when posting information such as credit card numbers.

When overriding this method, read the request data, write the response headers, get the response's writer or output stream object, and finally, write the response data. It's best to include content type and encoding. When using a PrintWriter object to return the response, set the content type before accessing the PrintWriter object.

The servlet container must write the headers before committing the response, because in HTTP the headers must be sent before the response body.

Where possible, set the Content-Length header (with the javax.servlet.ServletResponse.setContentLength method), to allow the servlet container to use a persistent connection to return its response to the client, improving performance. The content length is automatically set if the entire response fits inside the response buffer.

When using HTTP 1.1 chunked encoding (which means that the response has a Transfer-Encoding header), do not set the Content-Length header.

This method does not need to be either safe or idempotent. Operations requested through POST can have side effects for which the user can be held accountable, for example, updating stored data or buying items online.

If the HTTP POST request is incorrectly formatted, doPost returns an HTTP "Bad Request" message.
Parameters:
  req - an HttpServletRequest object thatcontains the request the client has madeof the servlet
Parameters:
  resp - an HttpServletResponse object thatcontains the response the servlet sendsto the client
exception:
  IOException - if an input or output error is detected when the servlet handlesthe request
exception:
  ServletException - if the request for the POSTcould not be handled
See Also:   javax.servlet.ServletOutputStream
See Also:   javax.servlet.ServletResponse.setContentType




doPut
protected void doPut(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException(Code)
Called by the server (via the service method) to allow a servlet to handle a PUT request. The PUT operation allows a client to place a file on the server and is similar to sending a file by FTP.

When overriding this method, leave intact any content headers sent with the request (including Content-Length, Content-Type, Content-Transfer-Encoding, Content-Encoding, Content-Base, Content-Language, Content-Location, Content-MD5, and Content-Range). If your method cannot handle a content header, it must issue an error message (HTTP 501 - Not Implemented) and discard the request. For more information on HTTP 1.1, see RFC 2616 .

This method does not need to be either safe or idempotent. Operations that doPut performs can have side effects for which the user can be held accountable. When using this method, it may be useful to save a copy of the affected URL in temporary storage.

If the HTTP PUT request is incorrectly formatted, doPut returns an HTTP "Bad Request" message.
Parameters:
  req - the HttpServletRequest object thatcontains the request the client made ofthe servlet
Parameters:
  resp - the HttpServletResponse object thatcontains the response the servlet returnsto the client
exception:
  IOException - if an input or output error occurswhile the servlet is handling thePUT request
exception:
  ServletException - if the request for the PUTcannot be handled




doTrace
protected void doTrace(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException(Code)
Called by the server (via the service method) to allow a servlet to handle a TRACE request. A TRACE returns the headers sent with the TRACE request to the client, so that they can be used in debugging. There's no need to override this method.
Parameters:
  req - the HttpServletRequest object thatcontains the request the client made ofthe servlet
Parameters:
  resp - the HttpServletResponse object thatcontains the response the servlet returnsto the client
exception:
  IOException - if an input or output error occurswhile the servlet is handling theTRACE request
exception:
  ServletException - if the request for theTRACE cannot be handled



getLastModified
protected long getLastModified(HttpServletRequest req)(Code)
Returns the time the HttpServletRequest object was last modified, in milliseconds since midnight January 1, 1970 GMT. If the time is unknown, this method returns a negative number (the default).

Servlets that support HTTP GET requests and can quickly determine their last modification time should override this method. This makes browser and proxy caches work more effectively, reducing the load on server and network resources.
Parameters:
  req - the HttpServletRequest object that is sent to the servlet a long integer specifyingthe time the HttpServletRequestobject was last modified, in millisecondssince midnight, January 1, 1970 GMT, or-1 if the time is not known




service
protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException(Code)
Receives standard HTTP requests from the public service method and dispatches them to the doXXX methods defined in this class. This method is an HTTP-specific version of the javax.servlet.Servlet.service method. There's no need to override this method.
Parameters:
  req - the HttpServletRequest object thatcontains the request the client made ofthe servlet
Parameters:
  resp - the HttpServletResponse object thatcontains the response the servlet returnsto the client
exception:
  IOException - if an input or output error occurswhile the servlet is handling theHTTP request
exception:
  ServletException - if the HTTP requestcannot be handled
See Also:   javax.servlet.Servlet.service



service
public void service(ServletRequest req, ServletResponse res) throws ServletException, IOException(Code)
Dispatches client requests to the protected service method. There's no need to override this method.
Parameters:
  req - the HttpServletRequest object thatcontains the request the client made ofthe servlet
Parameters:
  res - the HttpServletResponse object thatcontains the response the servlet returnsto the client
exception:
  IOException - if an input or output error occurswhile the servlet is handling theHTTP request
exception:
  ServletException - if the HTTP request cannotbe handled
See Also:   javax.servlet.Servlet.service



Methods inherited from javax.servlet.GenericServlet
public void destroy()(Code)(Java Doc)
public String getInitParameter(String name)(Code)(Java Doc)
public Enumeration getInitParameterNames()(Code)(Java Doc)
public ServletConfig getServletConfig()(Code)(Java Doc)
public ServletContext getServletContext()(Code)(Java Doc)
public String getServletInfo()(Code)(Java Doc)
public String getServletName()(Code)(Java Doc)
public void init(ServletConfig config) throws ServletException(Code)(Java Doc)
public void init() throws ServletException(Code)(Java Doc)
public void log(String msg)(Code)(Java Doc)
public void log(String message, Throwable t)(Code)(Java Doc)
abstract public void service(ServletRequest req, ServletResponse res) throws ServletException, IOException(Code)(Java Doc)

Methods inherited from java.lang.Object
native protected Object clone() throws CloneNotSupportedException(Code)(Java Doc)
public boolean equals(Object obj)(Code)(Java Doc)
protected void finalize() throws Throwable(Code)(Java Doc)
final native public Class getClass()(Code)(Java Doc)
native public int hashCode()(Code)(Java Doc)
final native public void notify()(Code)(Java Doc)
final native public void notifyAll()(Code)(Java Doc)
public String toString()(Code)(Java Doc)
final native public void wait(long timeout) throws InterruptedException(Code)(Java Doc)
final public void wait(long timeout, int nanos) throws InterruptedException(Code)(Java Doc)
final public void wait() throws InterruptedException(Code)(Java Doc)

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