[管理学]JAVA培训讲义.ppt

* * * * * * * * * * * * * * * * * Servlet Life Cycle Overview ? The Web container manages the life cycle of a servlet instance. These methods should not be called by your code. ? You can provide an implementation of these methods to manipulate the servlet instance or the resources it depends on. * The init Life Cycle Method ? The init method is called by the Web container when the servlet instance is first created. ? The Servlet specification guarantees that no requests will be processed by this servlet until the init method has completed. ? Override the init method when: ? You need to create or open any servlet-specific resources that you need for processing user requests ? You need to initialize the state of the servlet * The service Life Cycle Method ? The service method is called by the Web container to process a user request. ? The HttpServlet class implements the service method by dispatching to doGet, doPost, and so on depending on the HTTP request method (GET, POST, and so on). * * The ServletConfig API * The ServletConfig API ? The GenericServlet class implements the ServletConfig interface, which provides subclasses with direct access to the config delegate. ? The Web container calls the init(config) method, which is handled by the GenericServlet class. This method stores the config object (delegate) and then calls the init() method. ? Override the init() method in your servlet class. Do not override the init(config) method. ? The getInitParameter method provides the servlet with access to the initialization parameters for that servlet instance. These parameters are stored in the deployment descriptor. * * * * * * * 28 29 30 32 33 34 35 42 43 44 45 * * * * * * * * * * * * * * * * Servlets on theWeb Server Deployment diagram of a Web server with a Web container: * Execution of Java Servlets How servlets work with one request: * Execution of Java Servlets How servlets work with many requests: * Advantages and Disadvantages of Java Servlets ? Servlet