servlet/jsp随记

Posted 2020-11-20 suheng

Servlet接口

public interface Servlet {
    ......

    public void init(ServletConfig config) throws ServletException;

    public ServletConfig getServletConfig();

    public void service(ServletRequest req, ServletResponse res)
            throws ServletException, IOException;

    public String getServletInfo();

    public void destroy();

    ......
}

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RequestDispatcher接口

public interface RequestDispatcher {

    ......

   /**
     * Forwards a request from
     * a servlet to another resource (servlet, JSP file, or
     * html file) on the server. This method allows
     * one servlet to do preliminary processing of
     * a request and another resource to generate
     * the response.
     *
     * <p>For a <code>RequestDispatcher</code> obtained via 
     * <code>getRequestDispatcher()</code>, the <code>ServletRequest</code> 
     * object has its path elements and parameters adjusted to match
     * the path of the target resource.
     *
     * <p><code>forward</code> should be called before the response has been 
     * committed to the client (before response body output has been flushed). 
     * If the response already has been committed, this method throws
     * an <code>IllegalStateException</code>.
     * Uncommitted output in the response buffer is automatically cleared 
     * before the forward.
     *
     * <p>The request and response parameters must be either the same
     * objects as were passed to the calling servlet‘s service method or be
     * subclasses of the {@link ServletRequestWrapper} or
     * {@link ServletResponseWrapper} classes
     * that wrap them.
     *
     * <p>This method sets the dispatcher type of the given request to
     * <code>DispatcherType.FORWARD</code>.
     *
     * @param request a {@link ServletRequest} object that represents the
     * request the client makes of the servlet
     *
     * @param response a {@link ServletResponse} object that represents
     * the response the servlet returns to the client
     *
     * @throws ServletException if the target resource throws this exception
     *
     * @throws IOException if the target resource throws this exception
     *
     * @throws IllegalStateException if the response was already committed
     *
     * @see ServletRequest#getDispatcherType
     */
    public void forward(ServletRequest request, ServletResponse response)
        throws ServletException, IOException;

    /**
     *
     * Includes the content of a resource (servlet, JSP page,
     * HTML file) in the response. In essence, this method enables 
     * programmatic server-side includes.
     *
     * <p>The {@link ServletResponse} object has its path elements
     * and parameters remain unchanged from the caller‘s. The included
     * servlet cannot change the response status code or set headers;
     * any attempt to make a change is ignored.
     *
     * <p>The request and response parameters must be either the same
     * objects as were passed to the calling servlet‘s service method or be
     * subclasses of the {@link ServletRequestWrapper} or
     * {@link ServletResponseWrapper} classes that wrap them.
     *
     * <p>This method sets the dispatcher type of the given request to
     * <code>DispatcherType.INCLUDE</code>.
     *
     * @param request a {@link ServletRequest} object that contains the
     * client‘s request
     *
     * @param response a {@link ServletResponse} object that contains the
     * servlet‘s response
     *
     * @throws ServletException if the included resource throws this
     * exception
     *
     * @throws IOException if the included resource throws this exception
     *
     * @see ServletRequest#getDispatcherType
     */
    public void include(ServletRequest request, ServletResponse response)
        throws ServletException, IOException;
    ......
}

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JSP内置的对象

- request：封装客户端的请求，其中包含来自GET或POST请求的参数； 
- response：封装服务器对客户端的响应； 
- pageContext：通过该对象可以获取其他对象； 
- session：封装用户会话的对象； 
- application：封装服务器运行环境的对象； 
- out：输出服务器响应的输出流对象； 
- config：Web应用的配置对象； 
- page：JSP页面本身（相当于Java程序中的this）； 
- exception：封装页面抛出异常的对象

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