HttpServlet里的三个方法：service(HttpServletRequest req, HttpServletResponse resp) ，doGet(HttpServletRequest req, HttpServletResponse resp)， doPost（HttpServletRequest req, HttpServletResponse res)的区别和联系：
- 在servlet中默认情况下，无论你是get还是post 提交过来 都会经过service（）方法来处理，然后转向到doGet
- 或是doPost方法，我们可以查看HttpServlet 类的service方法： 我在tomcat的lib目录下，解压servlet-api.jar,然后用反编译软件把libjavaxservlethttp下的HttpServlet.class反编译，看里头的service（）方法的原代码：查看源码发现，httpservlet继承genericservlet并实现了service方法，从实现来看service起到了调度的作用。因此自定义servlet继承httpservlet不需要覆盖重写service方法，只需覆盖重写doget或者dopost方法。
- 注意，sun只是定义了servlet接口，而实现servlet接口的就是类似于tomcat的服务器，所以我是在tomcat的安装目录下找到实现的类。
public abstract class HttpServlet extends GenericServlet {
protected void service(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException
{
String method = req.getMethod();
if(method.equals("GET"))
{
long lastModified = getLastModified(req);
if(lastModified == -1L)
{
doGet(req, resp);
} else
{
long ifModifiedSince = req.getDateHeader("If-Modified-Since");
if(ifModifiedSince < (lastModified / 1000L) * 1000L)
{
maybeSetLastModified(resp, lastModified);
doGet(req, resp);
} else
{
resp.setStatus(304);
}
}
} else
if(method.equals("HEAD"))
{
long lastModified = getLastModified(req);
maybeSetLastModified(resp, lastModified);
doHead(req, resp);
} else
if(method.equals("POST"))
doPost(req, resp);
else
if(method.equals("PUT"))
doPut(req, resp);
else
if(method.equals("DELETE"))
doDelete(req, resp);
else
if(method.equals("OPTIONS"))
doOptions(req, resp);
else
if(method.equals("TRACE"))
{
doTrace(req, resp);
} else
{
String errMsg = lStrings.getString("http.method_not_implemented");
Object errArgs[] = new Object[1];
errArgs[0] = method;
errMsg = MessageFormat.format(errMsg, errArgs);
resp.sendError(501, errMsg);
}
}}
- 从上面可以看出 这里的service是用来转向的，但是如果你在自己的servlet类中覆盖了service方法，比如说你的service是这样的：
- Java代码
- 1.publicvoid service(ServletRequest req, ServletResponse res)
- 2. throws ServletException, IOException {
- 3. res.getOutputStream().print(
- 4. "image is <img src='images/downcoin.gif'></img><br>");
- 5. }
- 那么这时service就不是用来转向的，而是用来处理业务的，现在不论你的客户端是用pos还是get来请求此servlet
- 都会执行service方法也只能执行servlet方法，不会去执行doPost或是doGet方法。
- 比如说：你的客户端代码是：
- Java代码
- 1. <%@page contentType="text/html; charset=utf-8"%>
- 2. <html>
- 3. <head><title>选择</title></head>
- 4. <body>
- 5. 请选择你喜欢的水果：<br>
- 6. <form action ="Test" method = "post">
- 7. <input type="checkbox" name="fruit" value ="apple" >苹果<br>
- 8. <input type="checkbox" name="fruit" value ="orange">桔子<br>
- 9. <input type="checkbox" name="fruit" value ="mango">芒果<br>
- 10. <input type="submit" value="提交">
- 11. </form>
- 12. </body>
- 13. </html>
- 14.
- 15. 服务端servlet是：Test类
- 16.
- 17.import java.io.IOException;
- 18.
- 19.import javax.servlet.ServletException;
- 20.import javax.servlet.ServletOutputStream;
- 21.import javax.servlet.ServletRequest;
- 22.import javax.servlet.ServletResponse;
- 23.import javax.servlet.http.HttpServlet;
- 24.import javax.servlet.http.HttpServletRequest;
- 25.import javax.servlet.http.HttpServletResponse;
- 26.
- 27./**
- 28. * 演示service方法
- 29. */
- 30.publicclass Testextends HttpServlet {
- 31.
- 32.publicvoid service(ServletRequest req, ServletResponse res)
- 33. throws ServletException, IOException {
- 34. res.getOutputStream().print("This is the service");
- 35.
- 36. }
- 37.
- 38.protectedvoid doGet(HttpServletRequest request,
- 39. HttpServletResponse response)throws ServletException, IOException {
- 40. doPost(request,response);
- 41.
- 42. }
- 43.protectedvoid doPost(HttpServletRequest request,
- 44. HttpServletResponse response)throws ServletException, IOException {
- 45. ServletOutputStream out=response.getOutputStream();
- 46. String[] args=(String[])request.getParameterValues("fruit");
- 47. for(int i=0;i<args.length;i++){
- 48. out.print(args[i]+"<br>");
- 49. }
- 50.
- 51. }
- 52. }
- 点击提交后：页面输出结果为“This is the service“；