JDBC

1. JDBC

Java Database Connectivity: java 数据库连接

出现JDBC的原因：SUN公司提供一种数据库访问规则，规范，由于数据库的种类比较多，java语言的使用比较广泛，SUN公司提供了一种规范，让其他的数据库提供商去实现底层的访问规则，此时Java程序只需要使用SUN公司提供的JDBC驱动即可

 使用JDBC的步骤

1. 注册驱动

// 1. 注册驱动
DriverManager.registerDriver(new com.mysql.jdbc.Driver());
Class.forName("com.mysql.jdbc.Driver");

2. 建立连接

// 2. 建立连接：参数一：协议+访问的数据库，参数二：用户名，参数三：密码
con=DriverManager.getConnection("jdbc:mysql://localhost/category", "root", "root");

3. 创建statement

// 3. 创建statement,使用数据库，一定要用到这个对象
st = con.createStatement();

4. 执行sql,得到ResultSet

// 4. 执行查询，得到结果集

String sql = "select * from category";
rs = st.executeQuery(sql);

5. 遍历结果集

// 5. 遍历结果集
while (rs.next()) {
    int id = rs.getInt("cid");
    String name = rs.getString("cname");
    String cdesc = rs.getString("cdesc");
    System.out.println(id + "----------" + name + "--------" + cdesc);
}

6. 释放资源

package jdbc_util;

import java.sql.Connection;
import java.sql.SQLException;
import java.sql.Statement;
import java.sql.ResultSet;

public class JDBCUtil {
    public static void release(Connection con, Statement st, ResultSet rs){
        closeRs(rs);
        closeSt(st);
        closeCon(con);
    }
    
    private static void closeRs(ResultSet rs){
        try{
            if(rs != null){
                rs.close();
            }
        }catch(SQLException e){
            e.printStackTrace();
        }finally{
            rs = null;
        }
    }
    
    private static void closeSt(Statement st){
        try{
            if(st != null){
                st.close();
            }
        }catch(SQLException e){
            e.printStackTrace();
        }finally{
            st = null;
        }
    }
    
    private static void closeCon(Connection con){
        try{
            if(con != null){
                con.close();
            }
        }catch(SQLException e){
            e.printStackTrace();
        }finally{
            con = null;
        }
    }
}

 使用properties配置文件

1. 在src文件目录下声明一个文件xxx.properties里面的内容如下

2. 在工具类中，使用静态代码块

static{
    try{
        // 1. 创建一个属性配置对象
        Properties properties = new Properties();
        // 2. 使用类加载器，读取src文件下的资源文件
        InputStream is = JDBCUtil.class.getClassLoader().getResourceAsStream("jdbc.properties");    
        // 3. 导入输入流
        properties.load(is);
        // 4. 读取属性
        driverClass = properties.getProperty("driverClass");
        url = properties.getProperty("url");
        name = properties.getProperty("name");
        password = properties.getProperty("password");
    }catch(Exception e){
        e.printStackTrace();
    }
    
}

数据库的CRUD sql

insert:
    insert into category(cid, cname, cdesc) values(1, 'wang', 'niubi');
delete:
    delete from category where cid = 0;
query:
    select * from category;
update:
    update category set age = 30 where id = 1;

使用单元测试，测试代码

1. 定义各个类，Testxxx，里面定义方法：testxxx

2. 添加Junit支持, add library

3. 方法上添加@Test

4. 右键方法名字使用Junit运行

package day_01;

import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.Statement;
import org.junit.Test;
import jdbc_util.JDBCUtil;

public class UnitTest {
    @Test
    public void testQuery() {
        Connection con = null;
        Statement st = null;
        ResultSet rs = null;
        String sql = "select * from category";
        try {
            con = JDBCUtil.getCon();
            st = con.createStatement();
            rs = st.executeQuery(sql);
            while (rs.next()) {
                int id = rs.getInt("cid");
                String name = rs.getString("cname");
                String desc = rs.getString("cdesc");
                System.out.println("id:" + id + ",name:" + name + ",desc:" + desc);
            }
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
    
    @Test
    public void testInsert(){
        Connection con = null;
        Statement st = null;
        ResultSet rs = null;
        try{
            con = JDBCUtil.getCon();
            st = con.createStatement();
            String sql = "insert into category values(5, '海鲜鱼类', '小龙虾种种美食')";
            int result = st.executeUpdate(sql);
            if(result > 0){
                System.out.println("添加成功");
            }else{
                System.out.println("添加失败");
            }
        }catch(Exception e){
            e.printStackTrace();
        }
    }
    
    @Test
    public void testDelete(){
        Connection con = null;
        Statement st = null;
        ResultSet rs = null;
        try{
            con = JDBCUtil.getCon();
            st = con.createStatement();
            String sql = "delete from category where cid = 9";
            int result = st.executeUpdate(sql);
            if(result > 0){
                System.out.println("删除成功");
            }else{
                System.out.println("删除失败");
            }
        }catch(Exception e){
            e.printStackTrace();
        }
    }
    
    @Test
    public void testUpdate(){
        Connection con = null;
        Statement st = null;
        ResultSet rs = null;
        try{
            con = JDBCUtil.getCon();
            st = con.createStatement();
            String sql = "update category set cdesc = '吃货的天下' where cid = 4";
            int result = st.executeUpdate(sql);
            if(result > 0){
                System.out.println("更新成功");
            }else{
                System.out.println("更新失败");
            }
        }catch(Exception e){
            e.printStackTrace();
        }
    }
}

Dao模式

1. 新建一个dao接口，里面申明数据库访问规则

2. 新建一个dao实现类，具体时间早期定义的函数

3. 具体实现

public interface UserDao {
    /*
     * 查询数据库
     */
    void findAll();

}

public class UserDaoImpl implements UserDao{

    @Override
    public void findAll() {
        Connection con = null;
        Statement st = null;
        ResultSet rs = null;
        try {
            // 1. 获取连接对象
            con = JDBCUtil.getCon();
            // 2. 创建statement对象
            st = con.createStatement();
            String sql = "select * from product";
            // 3. 执行查询语句
            rs = st.executeQuery(sql);
            while(rs.next()){
                int id = rs.getInt("pid");
                String name = rs.getString("pname");
                String price = rs.getString("price");
                String cno = rs.getString("cno");
                System.out.println("id:" + id + ",name:" + name + ",price:" + price + ",cno:" + cno);
            }
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } finally{
            JDBCUtil.release(con, st, rs);
        }
        
    }
    
}

public class TestUserDaoImpl {
    @Test
    public void testFindAll(){
        UserDao dao = new UserDaoImpl();
        dao.findAll();
    }
}

 ##Statement的安全问题

1. Statement执行，实际上是拼接sql语句，先拼接sql语句，然后一起执行

2. PrepareStatement用来替换Statement对象

public interface UserDao {
    /*
     * 插入数据
     */
    void insert(String username, String password);
    /*
     * 查询数据库
     */
    void findAll();
    
    /*
     * 登陆数据库
     */
    void login(String username, String password);
    
    /*
     * 删除数据
     */
    void delete(int id);
    
    /*
     * 更新数据
     */
    void update(int id, String name);
}

public class UserDaoImpl implements UserDao{
    

    @Override
    public void findAll() {
        Connection con = null;
        Statement st = null;
        ResultSet rs = null;
        try {
            // 1. 获取连接对象
            con = JDBCUtil.getCon();
            // 2. 创建statement对象
            st = con.createStatement();
            String sql = "select * from student";
            // 3. 执行查询语句
            rs = st.executeQuery(sql);
            while(rs.next()){
                int id = rs.getInt("id");
                String username = rs.getString("username");
                String password = rs.getString("password");
                System.out.println("id:" + id + ",username:" + username + ",password:" + password);
            }
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } finally{
            JDBCUtil.release(con, st, rs);
        }
        
    }

    @Override
    public void login(String username, String password) {
        Connection con = null;
        PreparedStatement ps = null;
        ResultSet rs = null;
        
        try {
            con = JDBCUtil.getCon();
            String sql = "select * from student where username = ? and password = ?";
            // 将先对sql语句做语法的校验，?中的内容，不管传递什么，都把它看成是字符串
            ps = con.prepareStatement(sql);
            // ?对应的索引从1开始
            ps.setString(1, username);
            ps.setString(2, password);
            
            rs = ps.executeQuery();
            if(rs.next()){
                System.out.println("登陆成功");
            }else{
                System.out.println("登陆失败");
            }
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } finally{
            JDBCUtil.release(con, ps, rs);
        }
    }

    @Override
    public void insert(String username, String password) {
        PreparedStatement ps = null;
        Connection con = null;
        try {
            con = JDBCUtil.getCon();
            String sql = "insert into student values(?, ?, null)";
            ps = con.prepareStatement(sql);
            ps.setString(1, username);
            ps.setString(2, password);
            int result = ps.executeUpdate();
            if(result > 0){
                System.out.println("插入成功");
            }else{
                System.out.println("插入失败");
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally{
            JDBCUtil.release(con, ps);
        }
    }

    @Override
    public void delete(int id) {
        PreparedStatement ps = null;
        Connection con = null;
        try {
            con = JDBCUtil.getCon();
            String sql = "delete from student where id = ? ";
            ps = con.prepareStatement(sql);
            ps.setInt(1, id);
            int result = ps.executeUpdate();
            if(result > 0){
                System.out.println("删除成功");
            }else{
                System.out.println("删除失败");
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally{
            JDBCUtil.release(con, ps);
        }
    }

    @Override
    public void update(int id, String name) {
        Connection con = null;
        PreparedStatement ps = null;
        try{
            con = JDBCUtil.getCon();
            String sql = "update student set username = ? where id = ?";
            ps = con.prepareStatement(sql);
            ps.setString(1, name);
            ps.setInt(2, id);
            int result = ps.executeUpdate();
            if(result > 0){
                System.out.println("更新成功");
            }else{
                System.out.println("更新失败");
            }
        } catch(Exception e){
            e.printStackTrace();
        } finally{
            JDBCUtil.release(con, ps);
        }
    }
    
}

public class TestUserDaoImpl {
    @Test
    public void testFindAll(){
        UserDao dao = new UserDaoImpl();
        dao.findAll();
    }
    
    @Test
    public void testLogin(){
        UserDao dao = new UserDaoImpl();
        dao.login("wangjian", "2015141452153");
    }
    
    @Test
    public void testInsert(){
        UserDao dao = new UserDaoImpl();
        dao.insert("wjx", "2015141452155");
    }
    
    @Test
    public void testDelete(){
        UserDao dao = new UserDaoImpl();
        dao.delete(5);
    }
    
    @Test
    public void testUpdate(){
        UserDao dao = new UserDaoImpl();
        dao.update(5, "wangjingxuan");
    }
}

public class JDBCUtil {
    static String driverClass = null;
    static String url = null;
    static String name = null;
    static String password = null;
    
    static{
        try{
            // 1. 创建一个属性配置对象
            Properties properties = new Properties();
            // 2. 使用类加载器，读取src文件下的资源文件
            InputStream is = JDBCUtil.class.getClassLoader().getResourceAsStream("jdbc.properties");    
            // 3. 导入输入流
            properties.load(is);
            // 4. 读取属性
            driverClass = properties.getProperty("driverClass");
            url = properties.getProperty("url");
            name = properties.getProperty("name");
            password = properties.getProperty("password");
        }catch(Exception e){
            e.printStackTrace();
        }
        
    }
    
    public static Connection getCon(){
        Connection con = null;
        try {
            Class.forName(driverClass);    // 可以不写
            con = DriverManager.getConnection(url, name, password);
        } catch (Exception e) {
            e.printStackTrace();
        }
        return con;
    }
    
    public static void release(Connection con, Statement st, ResultSet rs){
        closeRs(rs);
        closeSt(st);
        closeCon(con);
    }
    
    public static void release(Connection con, Statement st){
        closeCon(con);
        closeSt(st);
    }
    
    
    private static void closeRs(ResultSet rs){
        try{
            if(rs != null){
                rs.close();
            }
        }catch(SQLException e){
            e.printStackTrace();
        }finally{
            rs = null;
        }
    }
    
    private static void closeSt(Statement st){
        try{
            if(st != null){
                st.close();
            }
        }catch(SQLException e){
            e.printStackTrace();
        }finally{
            st = null;
        }
    }
    
    private static void closeCon(Connection con){
        try{
            if(con != null){
                con.close();
            }
        }catch(SQLException e){
            e.printStackTrace();
        }finally{
            con = null;
        }
    }
}