servlet示例四：与数据库交互

背景：学生基本信息管理系统中，要求输出学生的基本信息情况。



更合理地完成任务需要做到以下三点：

1.创建Students类储存所有的学生信息（我把该类专门放在了adn.entities包内）

2.创建Students_dao类储存所有的工具比如说连接数据库的相关信息等（我把该类专门放在了adn.daos包内）

3.创建AllStuInfo类的servlet将查询的学生的信息显示在网页上（我把该类专门放在了adn.MyServlets包内）

出现的问题:尝试连线已失败

解决：由于我将conn=DriverManager.getConnection(url,"postgres","csy32384");用户名输入错误（少了一个s）导致的

下面就是对这三点代码的具体化：

步骤一：

package adn.entities;

public class Students {

private String sno,sname,sex;

public Students(String sno, String sname, String sex) {

super();

this.sno = sno;

this.sname = sname;

this.sex = sex;

}

public String getSex() {

return sex;

}

public void setSex(String sex) {

this.sex = sex;

}

public String getSno() {

return sno;

}

public void setSno(String sno) {

this.sno = sno;

}

public String getSname() {

return sname;

}

public void setSname(String sname) {

this.sname = sname;

}

}



步骤二：

package adn.daos;

import java.sql.Connection;

import java.sql.DriverManager;

import java.sql.PreparedStatement;

import java.sql.ResultSet;

import java.util.ArrayList;

import java.util.List;

import adn.entities.Students;

public class Students_dao {

public List<Students> getAllStudents(){

List<Students> list=null;

Connection conn=null;

try{

list=new ArrayList<Students>();

Class.forName("org.postgresql.Driver");

String url="jdbc:postgresql://localhost:5432/CSY";

conn=DriverManager.getConnection(url,"postgres","csy32384");

String SQL="select sno,sname,sex from students";

PreparedStatement pr=conn.prepareStatement(SQL);

ResultSet rs=pr.executeQuery();

while(rs.next()){

String sno=rs.getString(1);

String sname=rs.getString(2);

String sex=rs.getString(3);

Students student=new Students(sno,sname,sex);

list.add(student);

}

rs.close();

conn.close();

}

catch(Exception e){

System.out.println("错误1 "+e);

}

return list;

}

}



步骤三：

package adn.MyServlet;

import java.io.IOException;

import java.io.PrintWriter;

import java.util.List;

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 adn.daos.Students_dao;

import adn.entities.Students;

@WebServlet("/GetAllStu.do")

public class GetStuInfo extends HttpServlet {

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

response.setContentType("text/html; charset=UTF-8");

Students_dao sdao=new Students_dao();

List<Students> list=sdao.getAllStudents();

PrintWriter out=response.getWriter();

for(Students s:list){

out.print(s.getSno()+" ");

out.print(s.getSname()+" ");

out.print(s.getSex());

out.print("<br>");

}

}

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

doGet(request, response);

}

}