servlet使用JDBC访问数据库
文章目录
- 效果演示
- 一、访问步骤
- 二、项目搭建
- (1)sql语句
- (2)Emp实体类
- (3)mapper封装结果集
- (4)util工具包
- (5)conf配置
- 三、服务器端代码编写
- (1)查询QueryEmpServlet.java
- (2)添加AddEmpServlet.java
- (3)加载LoadEmpServlet.java
- (4)删除DeleteEmpServlet.java
- (5)查询QueryEmpServlet.java
- (6)修改UpdateEmpServlet.java
- 四、优化servlet(合并servlet)
- (1)优化servlet的方法
- (2)ActionServlet.java
效果演示
1
挺尴尬的,把电脑播放的音乐也给录进去了。
一、访问步骤
步骤一：将JDBC驱动(.jar文件)放到WEB-INF\lib下
原因：ClassLoader找到字节码文件，然后加载到JVM的方法区中，变成一个对象。Tomcat都有自己的类加载器，会去WEB-INF下面lib中找字节码文件。(jar包中的都是字节码文件.)
步骤二、编写JDBC代码，需要注意异常的处理
二、项目搭建
(1)sql语句
-- 创建t_emp表
CREATE TABLE t_emp(
id INT(4) PRIMARY KEY AUTO_INCREMENT,
NAME VARCHAR(20),
salary DOUBLE(7,2),
age INT (3)
);
INSERT INTO t_emp VALUES(1,'蔡小坤',5000.0,22);
INSERT INTO t_emp VALUES(2,'乔小萝',6000.0,22);
(2)Emp实体类
package entity;
/**
* Emp实体类
*
* @author QianliangGuo
*/
public class Emp {
private Integer id;
private String name;
private Double salary;
private Integer age;
public Emp() {
super();
// TODO Auto-generated constructor stub
}
public Emp(Integer id, String name, Double salary, Integer age) {
super();
this.id = id;
this.name = name;
this.salary = salary;
this.age = age;
}
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Double getSalary() {
return salary;
}
public void setSalary(Double salary) {
this.salary = salary;
}
public Integer getAge() {
return age;
}
public void setAge(Integer age) {
this.age = age;
}
@Override
public String toString() {
// TODO Auto-generated method stub
return super.toString();
}
}
(3)mapper封装结果集
RowMapper接口
package mapper;
import java.sql.ResultSet;
/**
* RowMapper接口
* 作用: 将ResultSet结果集封装成对象
*
* @author QianliangGuo
*/
public interface RowMapper<T> {
// 将ResultSet结果集封装成对象
public T mappreRow(ResultSet rs);
}
EmpRowMapper.java
package mapper;
import java.sql.ResultSet;
import java.sql.SQLException;
import entity.Emp;
/**
* 封装处理结果集
*/
public class EmpRowMapper implements RowMapper<Emp> {
@Override
public Emp mappreRow(ResultSet rs) {
Emp emp = new Emp();
try {
emp.setId(rs.getInt("id"));
emp.setName(rs.getString("name"));
emp.setSalary(rs.getDouble("salary"));
emp.setAge(rs.getInt("age"));
} catch (SQLException e) {
e.printStackTrace();
}
return emp;
}
}
(4)util工具包
JdbcTemplate.java
package util;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.util.ArrayList;
import java.util.List;
import mapper.RowMapper;
/**
* JdbucTemplate类
* 作用:封装了增删改查操作
*
* @author QianliangGuo
*/
public class JdbcTemplate<T> {
/*
* 1.单条结果查询select_one
* 2.多条结果查询select_more
* 3.增删改 updata
*
*/
static Connection conn = null;
static PreparedStatement pstm = null;
static ResultSet rs = null;
// 1.select_one
public T queryForObject(String sql, RowMapper<T> rm, Object... args) {
T t = null;
try {
conn = JdbcUtil3.getConnection();
pstm = conn.prepareStatement(sql);
if (args.length != 0) {
for (int i = 0; i < args.length; i++) {
pstm.setObject(i + 1, args[i]);
}
}
rs = pstm.executeQuery();
if (rs.next()) {
t = rm.mappreRow(rs);
}
} catch (Exception e) {
System.out.println("数据库连接异常");
} finally {
try {
JdbcUtil3.release(rs, pstm, conn);
} catch (Exception e) {
System.out.println("释放资源出现问题");
}
}
return t;
}
//2.select_more
public List<T> queryForList(String sql,RowMapper<T> rm,Object...args){
List<T> list = null;
try {
conn = JdbcUtil3.getConnection();
pstm = conn.prepareStatement(sql);
if (args.length != 0) {
for (int i = 0; i < args.length; i++) {
pstm.setObject(i + 1, args[i]);
}
}
rs = pstm.executeQuery();
list = new ArrayList();
while(rs.next()) {
T t = rm.mappreRow(rs);
list.add(t);
}
} catch (Exception e) {
System.out.println("数据库连接异常");
} finally {
try {
JdbcUtil3.release(rs, pstm,conn);
} catch (Exception e) {
System.out.println("释放资源出现问题");
}
}
return list;
}
//3.updata操作
public void update(String sql, Object... args) {
try {
//开启一个连接
conn = JdbcUtil3.getConnection();
pstm = conn.prepareStatement(sql);
// args的长度如果不是0,就说明有参数,那它就是个半成品
if (args.length != 0) {
for (int i = 0; i < args.length; i++) {
pstm.setObject(i + 1, args[i]);
}
}
pstm.executeUpdate();
} catch (Exception e) {
System.out.println("数据库异常!");
} finally {
try {
JdbcUtil3.release(null, pstm, conn);
} catch (Exception e) {
System.out.println("关闭连接异常!");
}
}
}
}
JdbcUtil3.java
package util;
import java.io.IOException;
import java.io.InputStream;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.Properties;
import javax.sql.DataSource;
import org.apache.commons.dbcp.BasicDataSourceFactory;
/**
* Jdbc工具类
* 1:properties配置文件 封装获取连接 释放资源 提高代码复用性√
* 2:类加载时加载驱动√
* 3:ThreadLocal控制事务√
* 4:连接池,提高资源利用率√
* 5:rowmapper封装 减少代码冗余×
* 6:template封装 减少dao层代码冗余×
* @author 郭乾亮1998
*
*/
public class JdbcUtil3 {
//声明连接池
static DataSource pool = null;
//创建properties
static Properties pro = new Properties();
//创建ThreadLocal,可以为同一个线程保存同一个连接,为不同线程保存不同的连接
private static ThreadLocal<Connection> tl = new ThreadLocal<Connection>();
//加载驱动
static{
InputStream is = null;
try {
is = JdbcUtil3.class.getResourceAsStream("/conf/dbcp.properties");
//加载文件
pro.load(is);
//Class.forName(pro.getProperty("driverClassName"));
//properties配置文件创建连接池
pool = BasicDataSourceFactory.createDataSource(pro);
} catch (Exception e) {
e.printStackTrace();
}finally{
try {
is.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
//获取连接
public static Connection getConnection() throws Exception{
Connection conn = tl.get();//获得当前线程中的连接
if(conn == null){//如果当前线程中没有连接
String url = pro.getProperty("url");
String user = pro.getProperty("username");
String password = pro.getProperty("password");
//创建连接
//conn = DriverManager.getConnection(url,user,password);
//通过连接池对象获得connection
conn = pool.getConnection();
//将连接保存到当前线程
tl.set(conn);
}
return conn;
}
//释放资源
public static void release(ResultSet rs,PreparedStatement pstm,Connection conn) throws Exception{
if(rs!=null){
rs.close();
}
if(pstm!=null){
pstm.close();
}
if(conn!=null){
conn.close();
tl.remove();//将连接从当前线程中移除
}
}
}
(5)conf配置
dbcp.properties
driverClassName=com.mysql.jdbc.Driver
url=jdbc\:mysql\://localhost\:3306/mybase?useUnicode\=true&characterEncoding\=utf-8
username=root
password=Hudie
initialSize=10
maxActive=50
maxIdle=20
minIdle=5
maxWait=60000
connectionProperties=useUnicode\=true;characterEncoding\=utf-8
defaultAutoCommit=true
defaultTransactionIsolation=READ_COMMITTED
三、服务器端代码编写
(1)查询QueryEmpServlet.java
package web;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.List;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import dao.EmpDao;
import dao.EmpDaoImpl;
import entity.Emp;
/**
* 查询emp
*
* @author QianliangGuo
*/
public class QueryEmpServlet extends HttpServlet {
EmpDao empDao = new EmpDaoImpl();
@Override
protected void service(HttpServletRequest request,HttpServletResponse response) throws ServletException, IOException {
// 查询所有员工记录
List<Emp> list = empDao.queryAllEmp();
//设置服务器端解码
response.setContentType("text/html;charset=utf-8");
PrintWriter out = response.getWriter();
out.println(" ");
out.println("ID 姓名 薪水 年龄 操作 ");
out.println("" + emp.getId() + " ");
out.println("" + emp.getName() + " ");
out.println("" + emp.getSalary() + " ");
out.println("" + emp.getAge() + " ");
out.println("" + "+emp.getName()+"')\">删除");
out.println(" ");
out.println("修改"+" ");
out.println(" ");
}
out.println("
");
out.println("
");
out.println("");
}
}
(2)添加AddEmpServlet.java
package web;
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import dao.EmpDao;
import dao.EmpDaoImpl;
import entity.Emp;
/**
* 添加emp
*
* @author QianliangGuo
*/
public class AddEmpServlet extends HttpServlet {
EmpDao empDao = new EmpDaoImpl();
@Override
protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
request.setCharacterEncoding("utf-8");
String name = request.getParameter("name");
String salary = request.getParameter("salary");
String age = request.getParameter("age");
Emp emp = new Emp(null,name,Double.parseDouble(salary),Integer.parseInt(age));
empDao.addEmp(emp);
//添加成功,重定向到queryEmp中
response.sendRedirect("queryEmp");
}
}
(3)加载LoadEmpServlet.java
package web;
/**
* 加载
*/
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import dao.EmpDao;
import dao.EmpDaoImpl;
import entity.Emp;
public class LoadEmpServlet extends HttpServlet {
EmpDao empDao = new EmpDaoImpl();
@Override
protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//依据想要修改的id,查询这个员工原有信息
String id = request.getParameter("id");
Emp emp = empDao.selectEmpById(Integer.parseInt(id));
//将员工信息回显到修改表单的页面
response.setContentType("text/html;charset=utf-8");
PrintWriter out = response.getWriter();
out.println(");
out.println("
");
out.println("姓名:
");
out.println("薪水:
");
out.println("年龄:
");
out.println("");
out.println("");
}
}
(4)删除DeleteEmpServlet.java
package web;
/**
* 加载
*/
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import dao.EmpDao;
import dao.EmpDaoImpl;
import entity.Emp;
public class LoadEmpServlet extends HttpServlet {
EmpDao empDao = new EmpDaoImpl();
@Override
protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//依据想要修改的id,查询这个员工原有信息
String id = request.getParameter("id");
Emp emp = empDao.selectEmpById(Integer.parseInt(id));
//将员工信息回显到修改表单的页面
response.setContentType("text/html;charset=utf-8");
PrintWriter out = response.getWriter();
out.println(");
out.println("
");
out.println("姓名:
");
out.println("薪水:
");
out.println("年龄:
");
out.println("");
out.println("");
}
}
(5)查询QueryEmpServlet.java
package web;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.List;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import dao.EmpDao;
import dao.EmpDaoImpl;
import entity.Emp;
/**
* 查询emp
*
* @author QianliangGuo
*/
public class QueryEmpServlet extends HttpServlet {
EmpDao empDao = new EmpDaoImpl();
@Override
protected void service(HttpServletRequest request,HttpServletResponse response) throws ServletException, IOException {
// 查询所有员工记录
List<Emp> list = empDao.queryAllEmp();
//设置服务器端解码
response.setContentType("text/html;charset=utf-8");
PrintWriter out = response.getWriter();
out.println(" ");
out.println("ID 姓名 薪水 年龄 操作 ");
out.println("" + emp.getId() + " ");
out.println("" + emp.getName() + " ");
out.println("" + emp.getSalary() + " ");
out.println("" + emp.getAge() + " ");
out.println("" + "+emp.getName()+"')\">删除");
out.println(" ");
out.println("修改"+" ");
out.println(" ");
}
out.println("
");
out.println("
");
out.println("");
}
}
(6)修改UpdateEmpServlet.java
package web;
/**
* 修改
*/
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import dao.EmpDao;
import dao.EmpDaoImpl;
import entity.Emp;
public class UpdateEmpServlet extends HttpServlet {
EmpDao empDao = new EmpDaoImpl();
@Override
protected void service(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
//设置服务端解码
request.setCharacterEncoding("utf-8");
//获得修改之后的Emp信息
String id = request.getParameter("id");
String name = request.getParameter("name");
String salary = request.getParameter("salary");
String age = request.getParameter("age");
Emp emp = new Emp(Integer.parseInt(id),name,Double.parseDouble(salary),Integer.getInteger(age));
//修改用户信息
empDao.updateEmp(emp);
//修改成功后重定向到员工列表queryEmp
response.sendRedirect("queryEmp");
}
}
四、优化servlet(合并servlet)
(1)优化servlet的方法
通过request.getRequestURI()方法获取请求资源路径
可以将所有操作请求处理合并到一个Servlet中,实现请求的分发。
String action = url.substring(url.lastIndexOf("/")+1,url.lastIndexOf("."));
修改web.xml
<servlet-mapping>
<servlet-name>actionServletservlet-name>
<url-pattern>*.dourl-pattern>
servlet-mapping>
(2)ActionServlet.java
package web;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.List;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import dao.EmpDao;
import dao.EmpDaoImpl;
import entity.Emp;
public class ActionServlet extends HttpServlet {
//创建dao层实例
EmpDao empDao = new EmpDaoImpl();
@Override
protected void service(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
//设置服务器端对客户端解码
request.setCharacterEncoding("utf-8");
//设置客户端编码
response.setContentType("text/html;charset=utf-8");
//创建输出流
PrintWriter out = response.getWriter();
//获取请求资源路径/ems/.do
String url = request.getRequestURI();
//切分url地址,保留addEmp
String uri = url.substring(url.lastIndexOf("/")+1,url.lastIndexOf("."));
if(uri.equals("queryEmp")){
/**
* 查询
*/
List<Emp> list = empDao.queryAllEmp();
out.println(" ");
out.println("ID 姓名 薪水 年龄 操作 ");
out.println("" + emp.getId() + " ");
out.println("" + emp.getName() + " ");
out.println("" + emp.getSalary() + " ");
out.println("" + emp.getAge() + " ");
out.println("" + "+emp.getName()+"')\">删除");
out.println(" ");
out.println("修改"+" ");
out.println(" ");
}
out.println("
");
out.println("
");
out.println("");
}else if(uri.equals("loadEmp")){
/**
* 加载
*/
//根据想要修改的id,查询这个员工原有信息
String id = request.getParameter("id");
Emp emp = empDao.selectEmpById(Integer.parseInt(id));
out.println(");
out.println("
");
out.println("姓名:
");
out.println("薪水:
");
out.println("年龄:
");
out.println("");
out.println("");
}else if(uri.equals("updateEmp")){
/**
* 修改
*/
//获得修改之后的Emp信息
String id = request.getParameter("id");
String name = request.getParameter("name");
String salary = request.getParameter("salary");
String age = request.getParameter("age");
Emp emp = new Emp(Integer.parseInt(id),name,Double.parseDouble(salary),Integer.getInteger(age));
//修改用户信息
empDao.updateEmp(emp);
//修改成功后重定向到员工列表queryEmp
response.sendRedirect("queryEmp.do");
}else if(uri.equals("addEmp")){
/**
* 添加
*/
String name = request.getParameter("name");
String salary = request.getParameter("salary");
String age = request.getParameter("age");
Emp emp = new Emp(null,name,Double.parseDouble(salary),Integer.parseInt(age));
empDao.addEmp(emp);
//添加成功,重定向到queryEmp中
response.sendRedirect("queryEmp.do");
}else if(uri.equals("deleteEmp")){
/**
* 删除
*/
//获得需要删除的id
String id = request.getParameter("id");
empDao.deleteEmp(Integer.parseInt(id));
//删除成功后重定向到员工列表
response.sendRedirect("queryEmp.do");
}
}
}