（1）几种Servlet

Servlet

  • 需要实现很多方法init、getServletConfig、service、getServletInfo、destroy
  • 我们一般只需要service方法 ``` package com.code.web;

import javax.servlet.*; import javax.servlet.annotation.WebServlet; import java.io.IOException;

@WebServlet(urlPatterns = “/demo”) public class HelloServlet implements Servlet {

  1. /**
  2.  * 被创建的时候，调用1次
  3.  * @param servletConfig
  4.  * @throws ServletException
  5.  */
  6. @Override
  7. public void init(ServletConfig servletConfig) throws ServletException {
  8.     System.out.println("init");
  9. }
  11. /**
  12.  * 获取ServletConfig配置对象
  13.  */
  14. @Override
  15. public ServletConfig getServletConfig() {
  16.     System.out.println("getServletConfig");
  17.     return null;
  18. }
  20. /**
  21.  * 调用的时候，多次调用多次执行
  22.  */
  23. @Override
  24. public void service(ServletRequest servletRequest, ServletResponse servletResponse) throws ServletException, IOException {
  25.     System.out.println("service");
  27. }
  29. @Override
  30. public String getServletInfo() {
  31.     System.out.println("getServletInfo");
  32.     return null;
  33. }
  35. /**
  36.  * 销毁的时候，执行1次
  37.  */
  38. @Override
  39. public void destroy() {
  40.     System.out.println("destroy");
  41. }

}

  1. <a name="BMEVr"></a>
  2. #### GenericServlet
  4. - GenericServlet只暴露service()

package com.code.web;

import javax.servlet.GenericServlet; import javax.servlet.ServletException; import javax.servlet.ServletRequest; import javax.servlet.ServletResponse; import javax.servlet.annotation.WebServlet; import java.io.IOException;

@WebServlet(“/demo2”) public class Servlet2 extends GenericServlet {

  1. @Override
  2. public void service(ServletRequest servletRequest, ServletResponse servletResponse) throws ServletException, IOException {
  3.     System.out.println("demo2");
  4. }

}

  1. <a name="zycfk"></a>
  2. #### HttpServlet
  4. - 对http协议的一种封装，简化操作

package com.code.web;

import javax.servlet.ServletException; import javax.servlet.annotation.WebServlet; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import java.io.IOException;

@WebServlet(“/demo3”) public class Servlet3 extends HttpServlet {

  1. @Override
  2. protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
  3.     super.doGet(req, resp);
  4.     System.out.println("doGet");
  5. }
  7. @Override
  8. protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
  9.     super.doPost(req, resp);
  10.     System.out.println("doPost");
  11. }

}

  2. - service方法封装成get、post
  1. protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
  2.     String method = req.getMethod();
  3.     long lastModified;
  4.     if (method.equals("GET")) {
  5.         lastModified = this.getLastModified(req);
  6.         if (lastModified == -1L) {
  7.             this.doGet(req, resp);
  8.         } else {
  9.             long ifModifiedSince;
  10.             try {
  11.                 ifModifiedSince = req.getDateHeader("If-Modified-Since");
  12.             } catch (IllegalArgumentException var9) {
  13.                 ifModifiedSince = -1L;
  14.             }
  16.             if (ifModifiedSince < lastModified / 1000L * 1000L) {
  17.                 this.maybeSetLastModified(resp, lastModified);
  18.                 this.doGet(req, resp);
  19.             } else {
  20.                 resp.setStatus(304);
  21.             }
  22.         }
  23.     } else if (method.equals("HEAD")) {
  24.         lastModified = this.getLastModified(req);
  25.         this.maybeSetLastModified(resp, lastModified);
  26.         this.doHead(req, resp);
  27.     } else if (method.equals("POST")) {
  28.         this.doPost(req, resp);
  29.     } else if (method.equals("PUT")) {
  30.         this.doPut(req, resp);
  31.     } else if (method.equals("DELETE")) {
  32.         this.doDelete(req, resp);
  33.     } else if (method.equals("OPTIONS")) {
  34.         this.doOptions(req, resp);
  35.     } else if (method.equals("TRACE")) {
  36.         this.doTrace(req, resp);
  37.     } else {
  38.         String errMsg = lStrings.getString("http.method_not_implemented");
  39.         Object[] errArgs = new Object[]{method};
  40.         errMsg = MessageFormat.format(errMsg, errArgs);
  41.         resp.sendError(501, errMsg);
  42.     }
  44. }

```