用mybatis實現簡單的CRUD
下面介紹如何用mybatis實現簡單的增刪改查功能,有兩種方式,一種是通過xml配置檔案實現,一種是通過註解實現。
仍然通過對user的操作進行說明,新建好專案並匯入jar包後,新建資料庫和表,並插入兩條記錄:
create database mybatis;
use mybatis;
CREATE TABLE users(id INT PRIMARY KEY AUTO_INCREMENT, NAME VARCHAR(20), age INT);
INSERT INTO users(NAME, age) VALUES('Tom', 12);
INSERT INTO users(NAME, age) VALUES ('Jack', 11);
建表成功:
新建實體類User.java
package com.mybatis.entities;
public class User {
private Integer id;
private String name;
private Integer age;
//getters and setters
@Override
public String toString() {
return "User [id=" + id + ", name=" + name + ", age=" + age + "]" ;
}
}
通過XML實現
新建對映檔案userMapper.xml:
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.mybatis.test2.userMapper">
<!-- 新增操作 -->
<insert id="addUser" parameterType="com.mybatis.entities.User">
insert into users(name,age)
values(#{name},#{age})
</insert>
<!-- 刪除操作 -->
<delete id="deleteUser" parameterType="int">
delete from users where
id=#{id}
</delete>
<!-- 更新操作 -->
<update id="updateUser" parameterType="com.mybatis.entities.User">
update users set name = #{name},age = #{age} where id = #{id}
</update>
<!-- 根據id查詢單個記錄 -->
<select id="getUserById" parameterType="int"
resultType="com.mybatis.entities.User">
select *
from users where id=#{id}
</select>
<!-- 查詢所有記錄 -->
<select id="getAllUsers" resultType="com.mybatis.entities.User">
select * from users
</select>
</mapper>
在mybatis配置檔案中註冊上述對映檔案:
<mappers>
<mapper resource="com/mybatis/test2/userMapper.xml" />
</mappers>
編寫測試類進行測試:
public class Test {
private SqlSessionFactory sessionFactory;
private SqlSession session;
@Before
public void init(){
//讀取配置檔案
String resource = "conf.xml";
InputStream is = this.getClass().getClassLoader().getResourceAsStream(resource);
//建立SqlSessionFactory和SqlSession
sessionFactory = new SqlSessionFactoryBuilder().build(is);
session = sessionFactory.openSession();
}
@After
public void free(){
session.commit();
session.close();
}
@org.junit.Test
public void testAddUser() {
String statement = "com.mybatis.test2.userMapper"+".addUser";
User user = new User(-1, "Alan", 25);
session.insert(statement, user);
}
@org.junit.Test
public void testDeleteUser() {
String statement = "com.mybatis.test2.userMapper"+".deleteUser";
session.delete(statement, 3);
}
@org.junit.Test
public void testUpdateUser() {
String statement = "com.mybatis.test2.userMapper"+".updateUser";
User user = new User(2,"Jim",19);
session.update(statement, user);
}
@org.junit.Test
public void testgetUserById() {
String statement = "com.mybatis.test2.userMapper"+".getUserById";
User user = session.selectOne(statement, 1);
System.out.println(user);
}
@org.junit.Test
public void testgetAllUsers() {
String statement = "com.mybatis.test2.userMapper"+".getAllUsers";
List<User> list = session.selectList(statement);
System.out.println(list);
}
}
注意點:
1. 在對映檔案中,當parameterType=”int”時,sql語句中的引數名可以隨便定義,例如#{id},#{_id}都可以;但是當parameterType=”com.mybatis.entities.User”時,sql語句中的引數名需要和User類中的對應欄位名一致,例如#{id}對應User類中的欄位id,而不能寫成#{_id}。
2. 在對映檔案中定義getAllUsers時,只需要指明返回的集合中的元素的型別,即僅需要指明resultType=”com.mybatis.entities.User”就可以了。
通過註解實現
新建介面UserMapper.java:
public interface UserMapper {
@Insert("insert into users(name,age) values(#{name},#{age})")
public int addUser(User user);
@Delete("delete from users where id=#{id}")
public int deleteUser(int id);
@Update("update users set name=#{name},age=#{age} where id=#{id}")
public int updateUser(User user);
@Select("select * from users where id=#{id}")
public User getUserById(int id);
@Select("select * from users")
public List<User> getAllUsers();
}
在mybatis配置檔案中註冊該介面:
<mappers>
<mapper class="com.mybatis.test3.UserMapper"/>
</mappers>
編寫測試列進行測試:
public class Test {
private SqlSessionFactory sessionFactory;
private SqlSession session;
private UserMapper userMapper;
@Before
public void init(){
//讀取配置檔案
String resource = "conf.xml";
InputStream is = this.getClass().getClassLoader().getResourceAsStream(resource);
//建立SqlSessionFactory和SqlSession
sessionFactory = new SqlSessionFactoryBuilder().build(is);
session = sessionFactory.openSession();
//獲取UserMapper
userMapper = session.getMapper(UserMapper.class);
}
@After
public void free(){
session.commit();
session.close();
}
@org.junit.Test
public void testAddUser() {
User user = new User(-1, "Alan", 25);
userMapper.addUser(user);
}
@org.junit.Test
public void testDeleteUser() {
userMapper.deleteUser(9);
}
@org.junit.Test
public void testUpdateUser() {
User user = new User(2,"Jim",19);
userMapper.updateUser(user);
}
@org.junit.Test
public void testgetUserById() {
User user = userMapper.getUserById(1);
System.out.println(user);
}
@org.junit.Test
public void testgetAllUsers() {
List<User> list = userMapper.getAllUsers();
System.out.println(list);
}
}
可以優化的地方
一、連線資料庫的配置單獨放在一個properties檔案中:
新建配置檔案db.properties:
driver=com.mysql.jdbc.Driver
url=jdbc:mysql://localhost:3306/mybatis
name=你的資料庫使用者名稱
password=你的資料庫密碼
在mybatis配置檔案中配置:
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN" "http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
<properties resource="db.properties"/>
<environments default="development">
<environment id="development">
<transactionManager type="JDBC" />
<dataSource type="POOLED">
<property name="driver" value="${driver}" />
<property name="url" value="${url}" />
<property name="username" value="${name}" />
<property name="password" value="${password}" />
</dataSource>
</environment>
</environments>
<mappers>
...
</mappers>
</configuration>
二、 可以為實體類定義別名,以簡化對映檔案中的引用:
在mybatis配置檔案的configuration節點下配置:
<typeAliases>
<typeAlias type="com.mybatis.entities.User" alias="User"/>
</typeAliases>
那麼,當要在對映檔案引用User類的全類名時,只需要使用”User”即可,例如:
<!-- 新增操作 -->
<insert id="addUser" parameterType="User">
insert into users(name,age)
values(#{name},#{age})
</insert>
當要定義別名的類比較多時,還有一種更方便的方法,在mybatis配置檔案的configuration節點下配置:
<typeAliases>
<package name="com.mybatis.entities"/>
</typeAliases>
這將宣告在對映檔案中,包com.mybatis.entities下的所有類都可以用簡單類名來替代全類名。
三、可以在src下加入log4j的配置檔案,列印日誌資訊:
首先需要先匯入log4j的jar包:
然後配置log4j,有兩種方法:
方法一、在src目錄下新建log4j.properties:
log4j.properties,
log4j.rootLogger=DEBUG, Console
#Console
log4j.appender.Console=org.apache.log4j.ConsoleAppender
log4j.appender.Console.layout=org.apache.log4j.PatternLayout
log4j.appender.Console.layout.ConversionPattern=%d [%t] %-5p [%c] - %m%n
log4j.logger.java.sql.ResultSet=INFO
log4j.logger.org.apache=INFO
log4j.logger.java.sql.Connection=DEBUG
log4j.logger.java.sql.Statement=DEBUG
log4j.logger.java.sql.PreparedStatement=DEBUG
方法二、在src目錄下新建log4j.xml:
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE log4j:configuration SYSTEM "log4j.dtd">
<log4j:configuration xmlns:log4j="http://jakarta.apache.org/log4j/">
<appender name="STDOUT" class="org.apache.log4j.ConsoleAppender">
<layout class="org.apache.log4j.PatternLayout">
<param name="ConversionPattern" value="%-5p %d{MM-dd HH:mm:ss,SSS} %m (%F:%L) \n" />
</layout>
</appender>
<logger name="java.sql">
<level value="debug" />
</logger>
<logger name="org.apache.ibatis">
<level value="debug" />
</logger>
<root>
<level value="debug" />
<appender-ref ref="STDOUT" />
</root>
</log4j:configuration>
然後當執行sql操作時就會在控制檯列印sql語句。
解決欄位名與實體類屬性名不相同的衝突
在上面的例子中,我們在對映檔案中按一下方式定義select操作時:
<select id="getUserById" parameterType="int"
resultType="User">
select *
from users where id=#{id}
</select>
之所以能夠查詢成功併成功返回一個User物件,是因為實體類User的欄位名和表users的列名完全一致:
User類:
users表:
當它們不一致時,就無法通過這種方式達到預期的效果。這個問題有兩種解決辦法,為了進行說明,我們先定義列名和欄位名不一致的表orders和類Order:
新建表,並插入三條記錄:
CREATE TABLE orders(
order_id INT PRIMARY KEY AUTO_INCREMENT,
order_no VARCHAR(20),
order_price FLOAT
);
INSERT INTO orders(order_no, order_price) VALUES('aaaa', 23);
INSERT INTO orders(order_no, order_price) VALUES('bbbb', 33);
INSERT INTO orders(order_no, order_price) VALUES('cccc', 22);
新建實體類:
public class Order {
private int id;
private String orderNo;
private float price;
//getters and setters
@Override
public String toString() {
return "Order [id=" + id + ", orderNo=" + orderNo + ", price=" + price + "]";
}
public Order(int id, String orderNo, float price) {
super();
this.id = id;
this.orderNo = orderNo;
this.price = price;
}
public Order() {
super();
}
}
在這個例子中,orders表的列為order_id,order_no,order_price,Order類的對應欄位名分別為id,orderNo,price,解決方法如下:
方法一、通過在對映檔案的sql語句中定義別名:
<select id="getOrder" parameterType="int" resultType="Order">
select order_no orderNo,order_price price from orders where order_id=#{id}
</select>
方法二: 通過對映檔案中節點的resultMap屬性:
<select id="getAllOrders" resultMap="orderResultMap">
select * from orders
</select>
<resultMap type="Order" id="orderResultMap">
<id property="id" column="order_id" />
<result property="orderNo" column="order_no" />
<result property="price" column="order_price"/>
</resultMap>
其中,select節點中的resultMap需要和resultMap節點的id對應。在resultMap節點下,主鍵使用id節點,普通屬性使用result節點,其中property指實體類中的欄位名,column指資料庫表中對應的列名。