content
1. Create a database connection and close resources
2. Create a javaBean to encapsulate the results queried in the database into objects through mapping
5. Encapsulate the code in the test class and complete the test
A good day starts with prostitution
1. Create a database connection and close resources
package com.jdbc.JDBCUtil;
import java.sql.*;
public class JDBCUtils {
/**
* 获取数据库连接
* @return 返回数据库连接对象
* @throws Exception
*/
public static Connection getConnection() throws Exception {
//1,注册驱动
Class.forName("com.mysql.cj.jdbc.Driver");
String url = "jdbc:mysql://localhost:3306/jdbc_db";
String user = "root";
String password = "3.141592654";
//获取数据连接对象
Connection conn = DriverManager.getConnection(url, user, password);
return conn;
}
/**
* 关闭流的操作
* @param conn
* @param st
*/
public static void closeResource(Connection conn, Statement st){
try {
if (conn != null){
conn.close();
}
if (st != null){
st.close();
}
} catch (SQLException e) {
e.printStackTrace();
}
}
public static void closeResource(Connection conn, Statement st, ResultSet res){
try {
if (conn != null){
conn.close();
}
if (st != null){
st.close();
}
if (res != null){
res.close();
}
} catch (SQLException e) {
e.printStackTrace();
}
}
}
2. Create a javaBean to encapsulate the results queried in the database into objects through mapping
package com.jdbc.bean;
public class User {
private int userId;
private String userName;
public User() {
}
public User(int id, String name) {
this.userId = id;
this.userName = name;
}
public int getUserId() {
return userId;
}
public void setUserId(int userId) {
this.userId = userId;
}
public String getUserName() {
return userName;
}
public void setUserName(String userName) {
this.userName = userName;
}
@Override
public String toString() {
return "User{" +
"id=" + userId +
", name='" + userName + '\'' +
'}';
}
}
3. Data query operation
package com.jdbc.connection;
import com.jdbc.JDBCUtil.JDBCUtils;
import com.jdbc.bean.User;
import com.sun.java.accessibility.util.EventID;
import jdk.nashorn.internal.scripts.JD;
import org.junit.Test;
import javax.sql.rowset.JdbcRowSet;
import java.lang.reflect.Field;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.util.ArrayList;
import java.util.List;
import static com.jdbc.JDBCUtil.JDBCUtils.*;
public class PrepareStatementTest {
@Test
public void testSelectTab() throws Exception {
String sql = "select id userId,name userName from user_tab";
List<User> userList = selectManyInfo(User.class, sql);
//拉姆达表达式
userList.forEach(System.out::println);
}
@Test
public void testSelectAnyTab() throws Exception {
String sql = "select id userId,name userName from user_tab where id = ?";
User user = selectinfo(User.class, sql, 103);
System.out.println(user);
}
@Test
public void testUpdate(){
String sql = "update user_tab set name = ? where id = ?";
update(sql,"诸葛亮",102);
}
/**
* 通行的方法实现增删改
* @param sql 增删改语句
* @param args 占位符？个数不一定，根据sql占位符的个数，传入对应数量object
*/
public static int update(String sql,Object... args){
int temp = -1;
Connection conn = null;
PreparedStatement pst = null;
try{
//1.获取数据库连接
conn = getConnection();
//2.预编译sql语句
pst = conn.prepareStatement(sql);
//3.填充占位符
for (int i = 0; i < args.length; i++) {
pst.setObject(i+1,args[i]);
}
//4.执行
/*
pst.execute();如果是查询操作返回的是true
如果是更新操作返回的是false；
pst.executeUpdate();返回执行操作以后受影响的行数
*/
// pst.execute();
temp = pst.executeUpdate();
}catch (Exception e){
e.printStackTrace();
}finally {
//5.释放资源
closeResource(conn,pst);
}
return temp;
}
/**
* 查询一条记录
* @param tClass 表对应的类对象
* @param sql 查询语句
* @param args 占位符，个数不定
* @param <T> 泛型
* @return 将查询的结果封装一个对象并返回
* @throws Exception
*/
public static <T> T selectinfo(Class<T> tClass, String sql, Object... args) throws Exception {
Connection conn = null;
PreparedStatement pst = null;
ResultSet res = null;
try{
//获取数据库连接
conn = getConnection();
//预编译sql语句
pst = conn.prepareStatement(sql);
for (int i = 0; i < args.length; i++) {
pst.setObject(i+1,args[i]);
}
//执行sql语句
res = pst.executeQuery();
//获取结果集的元数据
ResultSetMetaData metaData = res.getMetaData();
//获取结果集列数
int colCount = metaData.getColumnCount();
//处理查询结果集
if (res.next()){
T t = tClass.newInstance();//利用反射来创建对象，newInstance()公共方法，每个类都要求实现
for (int i = 0; i < colCount; i++) {
//获取列值,列名
Object colValue = res.getObject(i+1);
String colLabel = metaData.getColumnLabel(i+1);
//利用反射机制来找到对应的类
Field field = tClass.getDeclaredField(colLabel);
field.setAccessible(true);
field.set(t,colValue);
}
return t;
}
}catch (Exception e){
e.printStackTrace();
}finally {
JDBCUtils.closeResource(conn,pst,res);
}
return null;
}
/**
* 查询多条记录
* @param tClass
* @param sql
* @param args
* @param <T>
* @return
*/
public static <T> List<T> selectManyInfo(Class<T> tClass, String sql, Object... args){
Connection conn = null;
PreparedStatement pst = null;
ResultSet res = null;
List<T> list = new ArrayList<>();
try {
//获取数据库连接对象
conn = getConnection();
//预编译sql语句
pst = conn.prepareStatement(sql);
//填充占位符
for (int i = 0; i < args.length; i++) {
pst.setObject(i+1,args[i]);
}
//执行sql语句
res = pst.executeQuery();
//获取res的元数据，查看结果集有几列
ResultSetMetaData metaData = res.getMetaData();
int colCount = metaData.getColumnCount();
//处理查询结果集
while (res.next()){//当res不为空时，将res指针下移，并都其中的数据
T t = tClass.newInstance();
for (int i = 0; i < colCount; i++) {
//获取列名
String colName = metaData.getColumnLabel(i + 1);
//获取列值
Object colValue = res.getObject(i + 1);
//利用反射机制创建对象
//将获取到的列名映射User类中相应的属性上
Field field = User.class.getDeclaredField(colName);
//将该属性设置为可读
field.setAccessible(true);
//为user对象的属性字段赋值
field.set(t,colValue);
}
list.add((T) t);
}
}catch (Exception e){
e.printStackTrace();
}finally {
JDBCUtils.closeResource(conn,pst,res);
}
return list;
}
}
There is a lady at the end of the article
4. Database update operation
/**
* 通行的方法实现增删改
* @param sql 增删改语句
* @param args 占位符？个数不一定，根据sql占位符的个数，传入对应数量object
*/
public static int update(String sql,Object... args){
int temp = -1;
Connection conn = null;
PreparedStatement pst = null;
try{
//1.获取数据库连接
conn = getConnection();
//2.预编译sql语句
pst = conn.prepareStatement(sql);
//3.填充占位符
for (int i = 0; i < args.length; i++) {
pst.setObject(i+1,args[i]);
}
//4.执行
/*
pst.execute();如果是查询操作返回的是true
如果是更新操作返回的是false；
pst.executeUpdate();返回执行操作以后受影响的行数
*/
// pst.execute();
temp = pst.executeUpdate();
}catch (Exception e){
e.printStackTrace();
}finally {
//5.释放资源
closeResource(conn,pst);
}
return temp;
}5. Encapsulate the code in the test class and complete the test
package com.jdbc.Test;
import com.jdbc.JDBCUtil.JDBCUtils;
import com.jdbc.bean.User;
import com.jdbc.connection.PrepareStatementTest;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.util.List;
import java.util.Scanner;
import static com.jdbc.connection.PrepareStatementTest.*;
public class Test {
public static void main(String[] args) throws Exception {
Scanner scanner = new Scanner(System.in);
System.out.println("请输入用户id");
int id = scanner.nextInt();
System.out.println("请输入用户名：");
String password = scanner.next();
String sql = "select id userId,name userName from user_tab where id = ? and name = ?";
User user = PrepareStatementTest.selectinfo(User.class, sql, id, password);
if (user == null){
System.out.println("登录失败");
}else {
System.out.println("登录成功");
Test test = new Test();
System.out.println("请输入要执行的操作：");
System.out.println("添加数据：1");
System.out.println("删除数据：2");
System.out.println("修改数据：3");
System.out.println("添加一条数据：4");
System.out.println("查询全部数据：5");
int input = scanner.nextInt();
switch (input){
case 1:
test.insertInfo();
break;
case 2:
test.deleteInfo();
break;
case 3:
test.updateInfo();
break;
case 4:
test.selectOneInfo();
break;
case 5:
test.selectAll();
break;
default:
System.out.println("输入有无，程序退出");
break;
}
}
}
//插入
public void insertInfo(){
String sql = "inset into user_tab values(?,?)";
System.out.println("请输入要添加id：");
Scanner scanner = new Scanner(System.in);
int userId = scanner.nextInt();
System.out.println("请输入要添加姓名：");
String userName = scanner.next();
int update = update(sql, userId, userName);
if (update > 0){
System.out.println("插入成功");
}else {
System.out.println("插入失败");
}
}
//删除
public void deleteInfo(){
String sql = "delete from user_tab where id = ?";
System.out.println("请输入要删除记录的id：");
Scanner scanner = new Scanner(System.in);
int id = scanner.nextInt();
int update = update(sql, id);
if (update > 0){
System.out.println("删除成功");
}else {
System.out.println("删除失败");
}
}
//修改
public void updateInfo(){
String sql = "update user_tab set set name = ? where id = ?";
System.out.println("输入要修改的id：");
Scanner scanner = new Scanner(System.in);
int id = scanner.nextInt();
System.out.println("输入用户名：");
String userName = scanner.next();
int update = update(sql, userName, id);
if (update > 0){
System.out.println("更新成功");
}else {
System.out.println("更新失败");
}
}
//查询一条数据
public void selectOneInfo() throws Exception {
String sql = "select id userId,name userName from user_tab where id = ?";
System.out.println("查询全部数据直接回车，否则输入id");
System.out.println("输入要查询的id");
Scanner scanner = new Scanner(System.in);
int id = scanner.nextInt();
User user = selectinfo(User.class, sql,id);
if (user == null){
System.out.println("查询结果不存在");
}else {
System.out.println(user);
}
}
//查询全部数据
public void selectAll() throws Exception {
String sql = "select id userId,name userName from user_tab";
List<User> users = selectManyInfo(User.class, sql);
if (users.size() == 0){
System.out.println("查询结果不存在");
}else {
users.forEach(System.out::println);
}
}
}
