【JDBC】预编译语句PreparedStatement

使用预编译，解决拼接sql 语句的问题。

  @Test
  public void preparedStatement() throws Exception{
      String sql = "insert into student (name,age) values (?,?)";
      Connection  connection = JdbcUtil.getConn();
      PreparedStatement preparedStatement = connection.prepareStatement(sql);
      preparedStatement.setString(1, "张三");
      preparedStatement.setInt(2, 24);
      preparedStatement.executeUpdate();
      JdbcUtil.close(connection, preparedStatement, null);
  }

操作Student表示列如下：

数据库操作Util：

package util;
import java.io.InputStream;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.Properties;


/***
 * 实现对JDBC 的封装
 * @author mqy
 *
 */
public class JdbcUtil {
    private static    Properties properties = new Properties();
    //使用静态代码块实现 jdbcUtil的字节码被加载锦jvm中 并且只执行一次。避免每次使用都注册
    static{
        try {
            InputStream inputStream = Thread.currentThread().getContextClassLoader().getResourceAsStream("db.properties");
            properties.load(inputStream);
            Class.forName(properties.getProperty("driverClassName"));
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
    private JdbcUtil() {
    }
    //提供外界访问 返回数据库的连接对象
    public static Connection getConn(){
        try {
            return DriverManager.getConnection(properties.getProperty("url"), properties.getProperty("username"), properties.getProperty("password"));
        } catch (Exception e) {
            e.printStackTrace();
        }
        return null;
    }    
    //关闭资源  查询方法关闭资源 JdbcUtil.close(conn,st,rs)
    //增删改 关闭资源JdbcUtil.close(conn,st,null)
    public static void close(Connection conn,Statement st,ResultSet rs){
        try {
            if (rs != null) {
                rs.close();
            }
        } catch (Exception e) {
            e.printStackTrace();
        }finally {
            try {
                if (st != null) {
                    st.close();
                }    
            } catch (Exception e2) {
                e2.printStackTrace();
            }finally {
                    try {
                        if (conn != null) {
                        conn.close();
                        }
                        } catch (Exception e) {
                        e.printStackTrace();
                    }
                }
            }
        }
}

properties文件：

driverClassName=com.mysql.jdbc.Driver
url=jdbc:mysql:///jdbcdemo
username=root
password=root

Student实体：

package somain;

public class Student {
    private String name;
    private Long id;
    private Integer age;
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public Long getId() {
        return id;
    }
    public void setId(Long id) {
        this.id = id;
    }
    public Integer getAge() {
        return age;
    }
    public void setAge(Integer age) {
        this.age = age;
    }
    @Override
    public String toString() {
        return "Student [name=" + name + ", id=" + id + ", age=" + age + "]";
    }
    public Student() {
        super();
    }
    public Student(String name, Integer age) {
        super();
        this.name = name;
        this.age = age;
    }
    
}

 

Dao：

package dao;


import java.util.List;

import somain.Student;

/**
 * 
 * 
 * */
public interface IStudentDao {
    /***
     * 保存学生对象
     * @param stu
     */
   void save(Student stu);
   /**
    * 删除指定ID 的学生信息
    * @param id
    */
   void delete(Long id);
   /***
    * 更新指定的学生信息
    * @param newStu
    */
   void update(Student newStu);
   /***
    * 查询指定id 的学生信息
    * @param id
    * @return
    */
   Student get(Long id);
   /***
    * 查询所有学生的对象，如果没有返回空集
    * @return
    */
   List<Student> list();

DaoImp：

package impl;

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.util.ArrayList;
import java.util.List;

import dao.IStudentDao;
import somain.Student;
import util.JdbcUtil;

public class StudentImpl implements IStudentDao {

    @Override
    public void save(Student stu) {
        String sql = "insert into student (name,age) values (?,?)";
        Connection connection = null;
        PreparedStatement preparedStatement = null;
        try {
            connection = JdbcUtil.getConn();
            preparedStatement = connection.prepareStatement(sql);
            preparedStatement.setString(1, stu.getName());
            preparedStatement.setInt(2, stu.getAge());
            preparedStatement.executeUpdate();

        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            JdbcUtil.close(connection, preparedStatement, null);
        }
        // TODO Auto-generated method stub

    }

    @Override
    public void delete(Long id) {
        String sql = "delete * from student where id =?";
        Connection connection = null;
        PreparedStatement preparedStatement = null;
        try {
            connection = JdbcUtil.getConn();
            preparedStatement = connection.prepareStatement(sql);
            preparedStatement.setLong(1, id);
            preparedStatement.executeUpdate();
            JdbcUtil.close(null, preparedStatement, null);
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            JdbcUtil.close(null, preparedStatement, null);
        }
        // TODO Auto-generated method stub

    }

    @Override
    public void update(Student newStu) {
        // TODO Auto-generated method stub
        String sql = "update student set name=? age= ? where id= ?";
        Connection connection = null;
        PreparedStatement preparedStatement = null;
        try {
            connection = JdbcUtil.getConn();
            preparedStatement = connection.prepareStatement(sql);
            preparedStatement.setString(1, newStu.getName());
            preparedStatement.setInt(2, newStu.getAge());
            preparedStatement.setLong(3, newStu.getId());
            preparedStatement.executeUpdate();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            JdbcUtil.close(connection, preparedStatement, null);
        }

    }

    @Override
    public Student get(Long id) {
        String sql = "select * from Student where id = ?";
        Connection connection = null;
        PreparedStatement preparedStatement = null;
        ResultSet set = null;
        try {
            connection = JdbcUtil.getConn();
            preparedStatement = connection.prepareStatement(sql);
            preparedStatement.setLong(1, id);
            set = preparedStatement.executeQuery();
            if (set.next()) {
                Student student = new Student();
                student.setAge(set.getInt("age"));
                student.setName(set.getString("name"));
                student.setId(set.getLong("id"));
                return student;
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            JdbcUtil.close(connection, preparedStatement, set);
        }
        // TODO Auto-generated method stub
        return null;
    }

    @Override
    public List<Student> list() {
        String sql = "select * from student";
        List<Student> list = new ArrayList<>();
        Connection connection = null;
        PreparedStatement preparedStatement = null;
        ResultSet resultSet = null;
        try {
            connection= JdbcUtil.getConn();
            preparedStatement = connection.prepareStatement(sql);
            resultSet = preparedStatement.executeQuery();
            while (resultSet.next()) {
                Student student = new Student();
                student.setAge(resultSet.getInt("age"));
                student.setName(resultSet.getString("name"));
                student.setId(resultSet.getLong("id"));
                list.add(student);
            }    
            
        } catch (Exception e) {
            e.printStackTrace();
        }finally {
            JdbcUtil.close(connection, preparedStatement, resultSet);
        }
        return list;
    }

}

Test：

package test;

import static org.junit.Assert.*;

import java.util.ArrayList;
import java.util.List;

import org.junit.Test;

import dao.IStudentDao;
import impl.StudentImpl;
import somain.Student;

public class StudentDaoTest {
    private    IStudentDao dao = new StudentImpl();
    @Test
    public void testSave() {
        //fail("Not yet implemented");
        Student stu = new Student();
        stu.setAge(30);
        stu.setName("lili");
        
        dao.save(stu);
    }
    @Test
    public void testUpdate(){
        Student student = new Student("lili", 45);
        student.setId(8L);
        dao.update(student);
    }
   
    @Test
    public void testDelete(){
    IStudentDao dao = new StudentImpl();
    dao.delete(12L);
        
    }
    @Test
    public void testGet(){
    Student student =     dao.get(8L);
    System.out.println(student);
    }
    @Test
    public void testList(){
        List list = new ArrayList<>();
        list = dao.list();
        System.out.println(list);
    }
 
}