一个Servlet是如何处理多个请求的? 一个Servlet是如何处理多个请求

1、servlet层

package com.ycz.controller; import com.alibaba.fastjson.JSON; import com.ycz.dao.PeopleDao; import com.ycz.domain.People; import javax.servlet.ServletException; import javax.servlet.ServletRequest; import javax.servlet.ServletResponse; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import java.io.IOException; import java.io.PrintWriter; import java.text.SimpleDateFormat; import java.util.Calendar; import java.util.Date; import java.util.List; /** * @Description * @ClassName MyServlet * @Author yanchengzhi * @date 2021.06.06 20:16 */public class MyServlet extends HttpServlet {PeopleDao peopleDao = new PeopleDao(); /** @description: servlet的核心方法，每个servlet请求都会经过此方法处理* @param: [req, res]* @return: void* @author: yanchengzhi* @date: 2021/6/14 10:52*/@Overridepublic void service(ServletRequest req, ServletResponse res) throws ServletException, IOException {HttpServletRequest request = (HttpServletRequest)req; HttpServletResponse response = (HttpServletResponse)res; String command = request.getParameter("COMMAND"); if("ADD".equals(command)) {addPeople(request,response); return; }if("UPDATE".equals(command)){updatePeople(request,response); return; }if("DEL".equals(command)) {deletePeople(request,response); return; }if("FIND".equals(command)) {findById(request,response); return; }if("FINDALL".equals(command)) {findAll(request,response); return; }}/** @description: 添加* @param: [request, response]* @return: void* @author: yanchengzhi* @date: 2021/6/14 10:51*/private void addPeople(HttpServletRequest request,HttpServletResponse response) throws IOException {People people = new People(); people.setName("云过梦无痕"); people.setBirth(new Date()); people.setTag(0); response.setContentType("text/html; charset=utf-8"); //response.setContentType("text/plain; charset=UTF-8"); PrintWriter writer = response.getWriter(); int res = peopleDao.addPeople(people); if(res > 0){writer.write("添加成功！"); } else {writer.write("添加失败！"); }writer.flush(); writer.close(); }/** @description: 修改* @param: [request, response]* @return: void* @author: yanchengzhi* @date: 2021/6/14 10:54*/private void updatePeople(HttpServletRequest request,HttpServletResponse response) throws IOException {// 获取修改记录的idInteger id = Integer.parseInt(request.getParameter("id")); People p = new People(); p.setName("yanchengzhi"); Calendar calendar = Calendar.getInstance(); calendar.set(1995,9,18); Date date = calendar.getTime(); p.setBirth(date); int res = peopleDao.updatePeople(p,id); response.setContentType("text/html; charset=utf-8"); PrintWriter writer = response.getWriter(); if(res > 0){writer.write("修改成功！"); } else {writer.write("修改成功！"); }writer.flush(); writer.close(); }/** @description: 删除记录* @param: [request, response]* @return: void* @author: yanchengzhi* @date: 2021/6/14 12:15*/private void deletePeople(HttpServletRequest request,HttpServletResponse response) throws IOException{Integer id = Integer.parseInt(request.getParameter("id")); int res = peopleDao.delPeople(id); response.setContentType("text/html; charset=utf-8"); PrintWriter writer = response.getWriter(); if(res > 0) {writer.write("删除成功！"); } else {writer.write("删除失败！"); }writer.flush(); writer.close(); }/** @description: 按照id查询* @param: [request, response]* @return: void* @author: yanchengzhi* @date: 2021/6/14 14:20*/private void findById(HttpServletRequest request,HttpServletResponse response) {Integer id = Integer.parseInt(request.getParameter("id")); People p = peopleDao.findById(id); if(p != null) {System.out.println("查找的记录信息如下："); System.out.println("-------------------"); System.out.println("Id号：" + p.getId()); System.out.println("姓名：" + p.getName()); SimpleDateFormat sdf = new SimpleDateFormat("yyyy年MM月dd日"); System.out.println("生日：" + sdf.format(p.getBirth())); System.out.println("Tag标记：" + p.getTag()); } else {System.out.println("查询的记录不存在！"); }}private void findAll(HttpServletRequest request,HttpServletResponse response) throws IOException{List list = peopleDao.findAll(); response.setContentType("text/plain; charset=utf-8"); PrintWriter writer = response.getWriter(); if(list != null && list.size() > 0){// 转为json串String jsonStr = JSON.toJSONString(list); writer.write(jsonStr); } else {writer.write("查无数据！"); }}}

关注重点是service方法里的这些代码：

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然后jsp中的代码如下：

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可以看到一个共同点，就是所有的a链接后面都带有一个COMMAND参数，只是绑定的值不一样，就是根据这个绑定的值，来进入到不同的业务方法中。
2、dao层代码

package com.ycz.dao; import com.ycz.conf.DataSourceManager; import com.ycz.domain.People; import java.sql.Connection; import java.sql.Date; import java.sql.PreparedStatement; import java.sql.ResultSet; import java.util.ArrayList; import java.util.List; /** * @Description数据访问层 * @ClassName PeopleDao * @Author yanchengzhi * @date 2021.06.08 08:50 */public class PeopleDao {/** @description: 添加* @param: [people]* @return: int* @author: yanchengzhi* @date: 2021/6/14 11:03*/public int addPeople(People people){int res = 0; String sql = "insert into people (name,birth,tag) values (?,UNIX_TIMESTAMP(?),?)"; Connection connection = DataSourceManager.getConnection(); PreparedStatement ps = null; try {ps = connection.prepareStatement(sql); ps.setString(1,people.getName()); ps.setDate(2,new Date(people.getBirth().getTime())); ps.setInt(3,people.getTag()); res = ps.executeUpdate(); } catch (Exception e){e.printStackTrace(); } finally {DataSourceManager.closeConnection(connection); DataSourceManager.closeStatement(ps); }return res; }/** @description: 修改* @param: [p, id]* @return: int* @author: yanchengzhi* @date: 2021/6/14 11:03*/public int updatePeople(People p, Integer id) {int res = 0; String sql = "update people set name = ?,birth = UNIX_TIMESTAMP(?) where id = ?"; Connection connection = DataSourceManager.getConnection(); PreparedStatement ps = null; try {ps = connection.prepareStatement(sql); ps.setString(1,p.getName()); ps.setDate(2,new Date(p.getBirth().getTime())); ps.setInt(3,id); res = ps.executeUpdate(); } catch (Exception e){e.printStackTrace(); } finally {DataSourceManager.closeConnection(connection); DataSourceManager.closeStatement(ps); }return res; }/** @description: 删除* @param: [id]* @return: int* @author: yanchengzhi* @date: 2021/6/14 12:20*/public int delPeople(Integer id) {int res = 0; String sql = "delete from people where id = ?"; Connection connection = DataSourceManager.getConnection(); PreparedStatement ps = null; try {ps = connection.prepareStatement(sql); ps.setInt(1,id); res = ps.executeUpdate(); } catch (Exception e) {e.printStackTrace(); } finally {DataSourceManager.closeConnection(connection); DataSourceManager.closeStatement(ps); }return res; }/** @description: 按照id查询* @param: [id]* @return: com.ycz.domain.People* @author: yanchengzhi* @date: 2021/6/14 14:20*/public People findById(Integer id) {String sql = "select id,name,FROM_UNIXTIME(birth) birthday,tag from people where id = ?"; Connection connection = DataSourceManager.getConnection(); PreparedStatement ps = null; ResultSet resultSet = null; try {ps = connection.prepareStatement(sql); ps.setInt(1,id); resultSet = ps.executeQuery(); while(resultSet.next()){People p = new People(); p.setId(resultSet.getInt("id")); p.setName(resultSet.getString("name")); p.setBirth(resultSet.getDate("birthday")); p.setTag(resultSet.getInt("tag")); return p; }} catch (Exception e) {e.printStackTrace(); } finally {DataSourceManager.closeConnection(connection); DataSourceManager.closeStatement(ps); DataSourceManager.closeResultSet(resultSet); }return null; }/** @description: 查询所有记录* @param: []* @return: java.util.List* @author: yanchengzhi* @date: 2021/6/14 14:43*/public List findAll() {List peoples = new ArrayList<>(); String sql = "select id,name,FROM_UNIXTIME(birth) birthday,tag from people"; Connection connection = DataSourceManager.getConnection(); PreparedStatement ps = null; ResultSet resultSet = null; try {ps = connection.prepareStatement(sql); resultSet = ps.executeQuery(); while(resultSet.next()){People p = new People(); p.setId(resultSet.getInt("id")); p.setName(resultSet.getString("name")); p.setBirth(resultSet.getDate("birthday")); p.setTag(resultSet.getInt("tag")); peoples.add(p); }} catch (Exception e) {e.printStackTrace(); } finally {DataSourceManager.closeConnection(connection); DataSourceManager.closeStatement(ps); DataSourceManager.closeResultSet(resultSet); }return peoples; }}

3、web.xml