spring-JDBC配置，使用，一些报错，mybatis原理，优化

一. 配置spring的jdbc的pom.xml遇到报错 missing artifactXXXXX。

修改dependency的版本如下

<dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-jdbc</artifactId>
        <version>3.1.1.RELEASE</version>
</dependency>

　

二.代码的execute执行方法报错，增加dependency如下：

<dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-tx</artifactId>
    <version>4.3.20.RELEASE</version>
</dependency>

　

三.代码执行报错　Caused by: org.xml.sax.SAXParseException; 

原因是设置的数据库的密码太复杂了，可能有一些标识符识别的问题，修改了一下数据库的密码。

		<!-- 连接数据库的用户名 -->
		<property name="username" value="root" />
		<property name="password" value="12345678"/>　　

四.xml中的mysql的driver的jar包没有导入，导致不能识别<property name="driverClassName" value="com.mysql.jdbc.Driver" />

增加dependency

<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <version>8.0.15</version>
</dependency>

其中还有一个问题，新增的这个connector的包版本比较新，报了一个错误：Loading class `com.mysql.jdbc.Driver'. This is deprecated. The new driver class is `com.mysql.cj.jdbc.Driver'.需要把xml中的value更新一下。

五.xml中配置的mysql的库是spring，数据库中并没有创建，出现报错：Could not get JDBC Connection; nested exception is java.sql.SQLSyntaxErrorException: Unknown database 'spring'

在mysql中创建一个spring的数据库就可以了

六.报错Could not get JDBC Connection; nested exception is java.sql.SQLException: The server time zone value 'Öйú±ê׼ʱ¼ä' is unrecognized or represents more than one time zone. You must configure either the server or JDBC driver (via the serverTimezone configuration property) to use a more specifc time zone value if you want to utilize time zone support.

原因是mysql的时区设置有问题，需要在mysql中修改。

打开mysql的命令行，执行语句：

mysql> show variables like '%time_zone%';
mysql> set global time_zone='+8:00'

　　

七 示例代码 

applicationContext.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:context="http://www.springframework.org/schema/context"
	xmlns:mvc="http://www.springframework.org/schema/mvc" 
	xmlns:aop="http://www.springframework.org/schema/aop"
	xsi:schemaLocation="http://www.springframework.org/schema/mvc 
 http://www.springframework.org/schema/mvc/spring-mvc-3.1.1.xsd
 http://www.springframework.org/schema/beans 
 http://www.springframework.org/schema/beans/spring-beans-4.3.xsd
 http://www.springframework.org/schema/context 
 http://www.springframework.org/schema/context/spring-context-4.3.xsd
 http://www.springframework.org/schema/aop
 http://www.springframework.org/schema/aop/spring-aop-4.3.xsd">
	<context:component-scan base-package="com.itheima" />
	<aop:aspectj-autoproxy />
	<!-- 配置数据源 -->
	<bean id="dataSource"
		class="org.springframework.jdbc.datasource.DriverManagerDataSource">
		<!-- 数据库驱动 -->
		<property name="driverClassName" value="com.mysql.cj.jdbc.Driver" />
		<!-- 连接数据库的url -->
		<property name="url" value="jdbc:mysql://localhost:3306/spring" />
		<!-- 连接数据库的用户名 -->
		<property name="username" value="root" />
		<property name="password" value="12345678"/>
	</bean>
	<!-- 将datasource注入到jdbcTemplate中 -->
	<bean id="jdbcTemplate" class="org.springframework.jdbc.core.JdbcTemplate">
		<property name="dataSource" ref="dataSource" />
	</bean>
	<!-- 将template注入到dao中 
	<bean id="xxx" class="Xxx">
		<property name="jdbcTemplate" ref="jdbcTemplate" />
	</bean>-->
</beans>
	　　

JdbcTemplateTest.java

package com.itheima.jdbcTemplate;

import org.apache.catalina.core.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
import org.springframework.jdbc.core.JdbcTemplate;

public class JdbcTemplateTest {
	public static void main(String[] args) {
		ClassPathXmlApplicationContext applicationContext = 
				new ClassPathXmlApplicationContext("com/itheima/jdbcTemplate/applicationContext.xml");
		JdbcTemplate jdTemplate = (JdbcTemplate) applicationContext.getBean("jdbcTemplate");
		jdTemplate.execute("create table account ( id int primary key auto_increment, username varchar(50), balance double)");
		System.out.println("账户表account创建成功");
	}
}

　　

pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
	<modelVersion>4.0.0</modelVersion>

	<groupId>com.example</groupId>
	<artifactId>demo</artifactId>
	<version>0.0.1-SNAPSHOT</version>

	<packaging>jar</packaging>
	<!-- <packaging>war</packaging> -->
	<name>demo</name>
	<description>Demo project for Spring Boot</description>


	<parent>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-parent</artifactId>
		<version>2.1.0.RELEASE</version>
		<relativePath /> <!-- lookup parent from repository -->
	</parent>

	<properties>
		<docker.image.prefix>spring-boot-yiibai</docker.image.prefix>
		<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
		<project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
		<java.version>1.8</java.version>
		<!-- 表明启动类 -->
		<start-class>com.example.demo.DemoApplication</start-class>
	</properties>

	<dependencies>
		<!-- https://mvnrepository.com/artifact/org.springframework/spring-aop -->

		<!-- https://mvnrepository.com/artifact/junit/junit -->
		<!-- https://mvnrepository.com/artifact/org.aspectj/aspectjrt -->
		<!-- https://mvnrepository.com/artifact/org.springframework/org.springframework.jdbc -->


		<dependency>
			<groupId>org.aspectj</groupId>
			<artifactId>aspectjrt</artifactId>
			<version>1.9.3</version>
		</dependency>
		<!-- https://mvnrepository.com/artifact/org.aspectj/aspectjweaver -->
		<dependency>
			<groupId>org.aspectj</groupId>
			<artifactId>aspectjweaver</artifactId>
			<version>1.9.3</version>
		</dependency>

		<dependency>
			<groupId>junit</groupId>
			<artifactId>junit</artifactId>
			<version>4.12</version>
			<scope>test</scope>
		</dependency>

		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter</artifactId>
		</dependency>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-thymeleaf</artifactId>
		</dependency>
		<!-- rest相关 -->
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-web</artifactId>

		</dependency>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-test</artifactId>
			<scope>test</scope>
		</dependency>
		<dependency>
			<groupId>org.springframework</groupId>
			<artifactId>spring-aop</artifactId>
			<version>4.3.6.RELEASE</version>
		</dependency>
	<dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-jdbc</artifactId>
        <version>3.1.1.RELEASE</version>
    </dependency>
    <!-- https://mvnrepository.com/artifact/mysql/mysql-connector-java 
    提供mysql的driver-->
<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <version>8.0.15</version>
</dependency>
    
<!-- 防止jdbcTemplate的execute方法调用报错 -->
<dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-tx</artifactId>
    <version>4.3.20.RELEASE</version>
</dependency>

	</dependencies>

	<build>
		<plugins>
			<plugin>
				<groupId>com.spotify</groupId>
				<artifactId>docker-maven-plugin</artifactId>
				<version>1.0.0</version>

				<configuration>
					<imageName>${docker.image.prefix}/${project.artifactId}</imageName>
					<dockerDirectory>src/main/docker</dockerDirectory>
					<resources>
						<resource>
							<directory>${project.build.directory}</directory>
							<include>${project.build.finalName}.jar</include>
						</resource>
					</resources>
				</configuration>
			</plugin>
			<plugin>
				<groupId>org.springframework.boot</groupId>
				<artifactId>spring-boot-maven-plugin</artifactId>
			</plugin>
		</plugins>
	</build>


</project>

　　

其他.  xml的配置太复杂了，数据库配置应该剥离出来的，后面估计要改。

一个正常的创建类--类对应数据库的表--操作表的接口--实现表的接口--测试代码，这个是数据库操作和代码触发都写在实现接口中，以后mybatis会分离数据库操作和实现操作。

mybatis的执行顺序和原理

mybatis示例代码

其中包括：dbProperties提取；mybatis注解

step1-1:

读取mybatis_config.xml配置，包括数据库配置，和ORM（对象-数据库关系映射）

<?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="mysql">
		<environment id = "mysql">
		<transactionManager type="JDBC"/>
		<dataSource type = "POOLED">
			<property name = "driver" value = "${jdbc.driver}"/>
			<property name = "url" value = "${jdbc.url}"/>
			<property name = "username" value = "${jdbc.username}"/>
			<property name = "password" value = "${jdbc.password}"/>
		</dataSource>
		</environment>
	</environments>
	<mappers>
		<mapper resource = "com/itheima/mapper/CustomerMapper.xml"/>
	</mappers>
</configuration>　　

step1-2

db.properties   配置的数据库信息

jdbc.driver=com.mysql.cj.jdbc.Driver
jdbc.url=jdbc:mysql://localhost:3306/mybatis
jdbc.username=root
jdbc.password=12345678

step1-3

CustomerMapper.xml   配置的ORM信息，包括一些操作数据库的语句。

<?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.itheima.mapper.CustomerMapper">
	<select id = "findCustomerById" parameterType="Integer"
	resultType="com.itheima.po.Customer">
		select * from t_customer where id = #{id}
	</select>
	<select id = "findCustomerByName" parameterType="String"
	resultType="com.itheima.po.Customer">
		select * from t_customer where username like concat('%',#{value},'%')
	</select>
	<insert id ="addCustomer" parameterType="com.itheima.po.Customer">
		insert into t_customer (username,jobs,phone)
		values(#{username},#{jobs},#{phone})
	</insert>
	<update id = "updateCustomer" parameterType="com.itheima.po.Customer">
		update t_customer set
		username = #{username},jobs=#{jobs},phone=#{phone}
		where id=#{id}
	</update>
</mapper>

　　

step2-1

创建会话工厂，与数据库建立连接（使用单例模式，仅创建一个sqlSessionFactory去连接数据库。如果创建多个，每次要加载全部的配置，耗时长，且容易消耗光数据库的资源（mysql.ini的max_connections参数））

参考： https://blog.csdn.net/xiaolizi22233/article/details/54172958

public class MybatisTest {
	private SqlSessionFactory sqlSessionFactory=null;
	String resource= "mybatis-config.xml";
	
	public SqlSessionFactory getSqlSessionFactory() throws IOException{
		if(sqlSessionFactory==null){
			InputStream inputStream = Resources.getResourceAsStream(resource);
			sqlSessionFactory=new SqlSessionFactoryBuilder().build(inputStream);
		}
		return sqlSessionFactory;
	}
}

　　

step2-2

创建sqlSession对象，该对象包含执行sql的所有方法（增删改查）

step3-1

mybatis底层定义了一个Executor接口操作数据库，根据sqlSession传递的参数，动态生成要执行的sql语句

step3-2

Executor接口的执行方法中，有一个MappedStatement类型的参数，该参数封装了sql语句的id，参数等（对应CustomerMapper.xml）

step4

输入参数映射，MappedStatement对象对输入参数进行定义，Executor通过MappedStatement在执行sql前，将输入的java对象映射到sql中

step5

输出参数映射，数据库执行完sql后，mappedStatement对输出结果定义（pojo，list，map,基本类型等），Executor将mappedStatement结果映射到java对象中

@Test
	public void findCustomerByIdTest() throws IOException{
		SqlSession sqlSession = getSqlSessionFactory().openSession();
//		sqlSession.selectOne("com.itheima.mapper.CustomerMapper.findCustomerById",1);
		Customer customer = sqlSession.selectOne("com.itheima.mapper.CustomerMapper.findCustomerById",1);
		System.out.println(customer.toString());
		sqlSession.close();
	}
	/**
	 * 模糊查询
	 * @throws IOException
	 */
	@Test
	public void findCustomerByNameTest() throws IOException{
		SqlSession sqlSession = getSqlSessionFactory().openSession();
//		sqlSession.selectOne("com.itheima.mapper.CustomerMapper.findCustomerById",1);
		List<Customer> customers = sqlSession.selectList("com.itheima.mapper.CustomerMapper.findCustomerByName","j");
		for(Customer customer:customers){
			System.out.println(customer);
		}
		sqlSession.close();
	}
	/**
	 * 插入数据
	 * @throws IOException 
	 */
  	@Test
	public void addCustomerTest() throws IOException{
		SqlSession sqlSession = getSqlSessionFactory().openSession();
//		sqlSession.selectOne("com.itheima.mapper.CustomerMapper.findCustomerById",1);
		Customer customer =new Customer();
		customer.setJobs("student");
		customer.setId(4);
		customer.setPhone("13242424028");
		customer.setUsername("jones");
		int rows=sqlSession.insert("com.itheima.mapper"
				+".CustomerMapper.addCustomer",customer);
		if(rows>0){
			System.out.println("您成功插入了"+rows+"条数据");
		}else{
			System.out.println("插入操作失败");
		}
//		System.out.println(customer.toString());
		sqlSession.commit();
		sqlSession.close();
	}
	/**
	 * 修改数据
	 */
	@Test
	public void updateCustomerTest()throws Exception{
		SqlSession sqlSession = getSqlSessionFactory().openSession();
//		sqlSession.selectOne("com.itheima.mapper.CustomerMapper.findCustomerById",1);
		Customer customer =new Customer();
		customer.setJobs("student");
		customer.setId(4);
		customer.setPhone("13000011122");
		customer.setUsername("jones");
		int rows=sqlSession.update("com.itheima.mapper"
				+".CustomerMapper.updateCustomer",customer);
		if(rows>0){
			System.out.println("您成功修改了"+rows+"条数据");
		}else{
			System.out.println("插入操作失败");
		}
//		System.out.println(customer.toString());
		sqlSession.commit();
		sqlSession.close();
	}

　　

 优化：

1. 配置mybatis插件，包括自动根据数据库表结构生成pojo类，DAO，xml；实现分页；追踪dao 接口和mapper文件里xml做一些基础变更

https://blog.csdn.net/Winstin1995/article/details/79679887

 还有一些其他插件，可以自行安装。

2.mapper.xml有很多标签，其中有<sql>可以用来定义一些常用字段

<sql id="customerColumns">id, username, jobs, phone</sql>

　　

<select id="findCustomerById" parameterType="Integer"
        resultType="com.itheima.po.Customer">
    select <include refid="customerColumns"/>    from t_customer
    where id = #{id}
</select>