JDBC簡單的CRUD操作

package com.jdbc.day01;

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

import org.junit.Test;

public class CRUD {
    @Test
    public void create(){
        Connection conn = null;
        Statement st = null;
        ResultSet rs = null;
        String sql = "create table user(id int not null auto_increment,username varchar(255),password varchar(255),sex varchar(255),age INTEGER,primary key(id))";
        JDBCUtils jdbc = JDBCUtils.getInstance();
        try {
            //創建連接
            conn=jdbc.getConnection();
            //創建執行sql語句
            st=conn.createStatement();
            //執行sql語句
            st.executeUpdate(sql);
        } catch (SQLException e) {
            e.printStackTrace();
        }finally{
            //關閉資源
            jdbc.free(conn, st, rs);
        }
    }
    @Test
    public void insert(){
        Connection conn = null;
        Statement st = null;
        ResultSet rs = null;
        String sql = "insert into user(username,password,sex,age)values('小f','123456','1','18')";
        JDBCUtils jdbc = JDBCUtils.getInstance();
        try {
            conn = jdbc.getConnection();
            st = conn.createStatement();
            st.executeUpdate(sql);
        } catch (SQLException e) {
            e.printStackTrace();
        }finally{
            jdbc.free(conn, st, rs);
        }
    }
    @Test
    public void read(){
        Connection conn=null;
        Statement st = null;
        ResultSet rs=null;
        JDBCUtils jdbc = JDBCUtils.getInstance();
        String sql = "select username,password,sex,age from user";
        try {
            conn=jdbc.getConnection();
            st = conn.createStatement();
            rs = st.executeQuery(sql);
            while(rs.next()){
                System.out.println(rs.getObject("username")+"\t"
                        +rs.getObject("password")+"\t"
                        +rs.getObject("sex")+"\t"
                        +rs.getObject("age")+"\t");
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }finally{
            jdbc.free(conn, st, rs);
        }

    }
    @Test
    public void update(){
        Connection conn=null;
        Statement st = null;
        ResultSet rs=null;
        JDBCUtils jdbc = JDBCUtils.getInstance();
        String sql = "update user set age = age+1 where id>3";
        try {
            conn=jdbc.getConnection();
            st = conn.createStatement();
            st.executeUpdate(sql);
        } catch (SQLException e) {
            e.printStackTrace();
        }finally{
            jdbc.free(conn, st, rs);
        }
    }

    @Test
    public void delete(){
        Connection conn=null;
        Statement st = null;
        ResultSet rs=null;
        JDBCUtils jdbc = JDBCUtils.getInstance();
        String sql = "delete from user where id>5";
        try {
            conn=jdbc.getConnection();
            st = conn.createStatement();
            st.executeUpdate(sql);
        } catch (SQLException e) {
            e.printStackTrace();
        }finally{
            jdbc.free(conn, st, rs);
        }
    }

    /*-----------------------------------------------------PreparedStatement防止sql注入，預編譯效率高---------------------------*/
    @Test
    public void psUpdate(){
        Connection conn=null;
        PreparedStatement ps = null;
        ResultSet rs=null;
        JDBCUtils jdbc = JDBCUtils.getInstance();
        String sql = "update user set password=? where id=?";
        try {
            conn=jdbc.getConnection();
            ps = conn.prepareStatement(sql);
            //爲每個問號賦值，1和2分別代表第一個問號和第二個問號
            ps.setString(1, "654321");
            ps.setString(2, "5");
            ps.executeUpdate();
        } catch (SQLException e) {
            e.printStackTrace();
        }finally{
            jdbc.free(conn, ps, rs);
        }
    }

}