Servlet从入门到精通三
一、HttpServlet和一些开发细节
Servlet接口与两个默认实现类：GenericServlet、HttpServlet
1、HttpServlet指能够处理HTTP请求的Servlet，它在原有Servlet接口上添加了一些与HTTP协议处理方法，它比Servlet接口的功能更为强大。因此开发人员在编写Servlet时，通常应该继承这个类，而避免直接去实现Servlet接口。
2、HttpServlet在实现Servlet接口时，覆写了service（）方法，改方法体内的代码会自动判断用户的请求方式，如为GET请求，则调用HttpServlet的doGet方法，如为Post请求，则调用doPost方法。因此，开发人员在编写Servlet时，通常只需要覆写doGet或doPost方法，而不要去覆写service方法。
查看servlet源码，看HttpServlet源码：
protected void service(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException {
String method = req.getMethod();
if (method.equals(METHOD_GET)) {
long lastModified = getLastModified(req);
if (lastModified == -1) {
doGet(req, resp);
} else {
long ifModifiedSince = req.getDateHeader(HEADER_IFMODSINCE);
if (ifModifiedSince < (lastModified / 1000 * 1000)) {
maybeSetLastModified(resp, lastModified);
doGet(req, resp);
} else {
resp.setStatus(HttpServletResponse.SC_NOT_MODIFIED);
}
}
} else if (method.equals(METHOD_HEAD)) {
long lastModified = getLastModified(req);
maybeSetLastModified(resp, lastModified);
doHead(req, resp);
} else if (method.equals(METHOD_POST)) {
doPost(req, resp);
} else if (method.equals(METHOD_PUT)) {
doPut(req, resp);
} else if (method.equals(METHOD_DELETE)) {
doDelete(req, resp);
} else if (method.equals(METHOD_OPTIONS)) {
doOptions(req,resp);
} else if (method.equals(METHOD_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(HttpServletResponse.SC_NOT_IMPLEMENTED, errMsg);
}
}
3、实例
1）建Web project
2）新建一个servlet，如下
3）点next，再点finish
4）写代码：
package cn.itcast;
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class ServletDemo1 extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
response.getOutputStream().write("Hello,HttpServlet!".getBytes());
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request, response); //这句话的意思：客户端不管是Get方式还是Post方式，都由doGet来响应。
}
}
5）、发布，打开Tomcat，浏览器中输入：
http://localhost:8088/JavaWebChuan/servlet/ServletDemo1，
可以看见 Hello,HttpServlet!
4、Myeclipse中改Servlet模板：
进到MyEclipse安装目录 D:\MyEclipse 7.0M1，搜索servlet.java
找到Servlet.java这个文件，把内容改为：
#---------------------------------------------#
#
#
#
#
#---------------------------------------------#
/**
* Constructor of the object.
*/
public
super();
}
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request,response);
}
/**
* The doPut method of the servlet.
*
* This method is called when a HTTP put request is received.
*
* @param request the request send by the client to the server
* @param response the response send by the server to the client
* @throws ServletException if an error occurred
* @throws IOException if an error occurred
*/
public void doPut(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
// Put your code here
}
/**
* The doDelete method of the servlet.
*
* This method is called when a HTTP delete request is received.
*
* @param request the request send by the client to the server
* @param response the response send by the server to the client
* @throws ServletException if an error occurred
* @throws IOException if an error occurred
*/
public void doDelete(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
// Put your code here
}
/**
* Initialization of the servlet.
*
* @throws ServletException if an error occurs
*/
public void init() throws ServletException {
// Put your code here
}
/**
* Destruction of the servlet.
*/
public void destroy() {
super.destroy(); // Just puts "destroy" string in log
// Put your code here
}
/**
* Returns information about the servlet, such as
* author, version, and copyright.
*
* @return String information about this servlet
*/
public String getServletInfo() {
return "This is my default servlet created by Eclipse";
}
保存，即可