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Spring Boot+MyBatis实现读写分离

时间:2020-05-22 09:19:54      阅读:52      评论:0      收藏:0      [点我收藏+]

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1.前言

读写分离要做的事情就是对于一条SQL该选择哪个数据库去执行,至于谁来做选择数据库这件事儿,无非两个,要么中间件帮我们做,要么程序自己做。因此,一般来讲,读写分离有两种实现方式。第一种是依靠中间件(比如:MyCat),也就是说应用程序连接到中间件,中间件帮我们做SQL分离;第二种是应用程序自己去做分离。这里我们选择程序自己来做,主要是利用Spring提供的路由数据源,以及AOP。

然而,应用程序层面去做读写分离最大的弱点(不足之处)在于无法动态增加数据库节点,因为数据源配置都是写在配置中的,新增数据库意味着新加一个数据源,必然改配置,并重启应用。当然,好处就是相对简单。

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2.AbstractRoutingDataSource

 

基于特定的查找key路由到特定的数据源。它内部维护了一组目标数据源,并且做了路由key与目标数据源之间的映射,提供基于key查找数据源的方法。

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3.实践

3.1.maven依赖

<?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.cjs.example</groupId>
    <artifactId>cjs-datasource-demo</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>jar</packaging>

    <name>cjs-datasource-demo</name>
    <description></description>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.0.5.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
        <java.version>1.8</java.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-aop</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-jdbc</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.mybatis.spring.boot</groupId>
            <artifactId>mybatis-spring-boot-starter</artifactId>
            <version>1.3.2</version>
        </dependency>
        <dependency>
            <groupId>org.apache.commons</groupId>
            <artifactId>commons-lang3</artifactId>
            <version>3.8</version>
        </dependency>

        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <scope>runtime</scope>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>


            <!--<plugin>
                <groupId>org.mybatis.generator</groupId>
                <artifactId>mybatis-generator-maven-plugin</artifactId>
                <version>1.3.5</version>
                <dependencies>
                    <dependency>
                        <groupId>mysql</groupId>
                        <artifactId>mysql-connector-java</artifactId>
                        <version>5.1.46</version>
                    </dependency>
                </dependencies>
                <configuration>
                    <configurationFile>${basedir}/src/main/resources/myBatisGeneratorConfig.xml</configurationFile>
                    <overwrite>true</overwrite>
                </configuration>
                <executions>
                    <execution>
                        <id>Generate MyBatis Artifacts</id>
                        <goals>
                            <goal>generate</goal>
                        </goals>
                    </execution>
                </executions>
            </plugin>-->

        </plugins>
    </build>
</project>

 

 

3.2. 数据源配置

application.yml

spring:
  datasource:
    master:
      jdbc-url: jdbc:mysql://192.168.1.16:3306/test
      username: root
      password: 123456
      driver-class-name: com.mysql.jdbc.Driver
    slave1:
      jdbc-url: jdbc:mysql://192.168.1.26:3306/test
      username: pig   # 只读账户
      password: 123456
      driver-class-name: com.mysql.jdbc.Driver
    slave2:
      jdbc-url: jdbc:mysql://192.168.1.36:3306/test
      username: pig   # 只读账户
      password: 123456
      driver-class-name: com.mysql.jdbc.Driver

 

 

多数据源配置

/**
 * 关于数据源配置,参考SpringBoot官方文档第79章《Data Access》
 * 79. Data Access
 * 79.1 Configure a Custom DataSource
 * 79.2 Configure Two DataSources
 */

@Configuration
public class DataSourceConfig {

    @Bean
    @ConfigurationProperties("spring.datasource.master")
    public DataSource masterDataSource() {
        return DataSourceBuilder.create().build();
    }

    @Bean
    @ConfigurationProperties("spring.datasource.slave1")
    public DataSource slave1DataSource() {
        return DataSourceBuilder.create().build();
    }

    @Bean
    @ConfigurationProperties("spring.datasource.slave2")
    public DataSource slave2DataSource() {
        return DataSourceBuilder.create().build();
    }

    @Bean
    public DataSource myRoutingDataSource(@Qualifier("masterDataSource") DataSource masterDataSource,
                                          @Qualifier("slave1DataSource") DataSource slave1DataSource,
                                          @Qualifier("slave2DataSource") DataSource slave2DataSource) {
        Map<Object, Object> targetDataSources = new HashMap<>();
        targetDataSources.put(DBTypeEnum.MASTER, masterDataSource);
        targetDataSources.put(DBTypeEnum.SLAVE1, slave1DataSource);
        targetDataSources.put(DBTypeEnum.SLAVE2, slave2DataSource);
        MyRoutingDataSource myRoutingDataSource = new MyRoutingDataSource();
        myRoutingDataSource.setDefaultTargetDataSource(masterDataSource);
        myRoutingDataSource.setTargetDataSources(targetDataSources);
        return myRoutingDataSource;
    }

}

 

 

这里,我们配置了4个数据源,1个master,2两个slave,1个路由数据源。前3个数据源都是为了生成第4个数据源,而且后续我们只用这最后一个路由数据源。

MyBatis配置

@EnableTransactionManagement
@Configuration
public class MyBatisConfig {
?
    @Resource(name = "myRoutingDataSource")
    private DataSource myRoutingDataSource;
?
    @Bean
    public SqlSessionFactory sqlSessionFactory() throws Exception {
        SqlSessionFactoryBean sqlSessionFactoryBean = new SqlSessionFactoryBean();
        sqlSessionFactoryBean.setDataSource(myRoutingDataSource);
        sqlSessionFactoryBean.setMapperLocations(new PathMatchingResourcePatternResolver().getResources("classpath:mapper/*.xml"));
        return sqlSessionFactoryBean.getObject();
    }
?
    @Bean
    public PlatformTransactionManager platformTransactionManager() {
        return new DataSourceTransactionManager(myRoutingDataSource);
    }
}?

 

 

由于Spring容器中现在有4个数据源,所以我们需要为事务管理器和MyBatis手动指定一个明确的数据源。

3.3.设置路由key / 查找数据源

目标数据源就是那前3个这个我们是知道的,但是使用的时候是如果查找数据源的呢?

首先,我们定义一个枚举来代表这三个数据源

package com.muding.example.enums;
?
public enum DBTypeEnum {
    MASTER, SLAVE1, SLAVE2;
}

 

 

接下来,通过ThreadLocal将数据源设置到每个线程上下文中

public class DBContextHolder {
?
    private static final ThreadLocal<DBTypeEnum> contextHolder = new ThreadLocal<>();
?
    private static final AtomicInteger counter = new AtomicInteger(-1);
?
    public static void set(DBTypeEnum dbType) {
        contextHolder.set(dbType);
    }
?
    public static DBTypeEnum get() {
        return contextHolder.get();
    }
?
    public static void master() {
        set(DBTypeEnum.MASTER);
        System.out.println("切换到master");
    }
?
    public static void slave() {
        //  轮询
        int index = counter.getAndIncrement() % 2;
        if (counter.get() > 9999) {
            counter.set(-1);
        }
        if (index == 0) {
            set(DBTypeEnum.SLAVE1);
            System.out.println("切换到slave1");
        }else {
            set(DBTypeEnum.SLAVE2);
            System.out.println("切换到slave2");
        }
    }
}

 

 

获取路由key

public class MyRoutingDataSource extends AbstractRoutingDataSource {
    @Nullable
    @Override
    protected Object determineCurrentLookupKey() {
        return DBContextHolder.get();
    }
}

 

设置路由key

默认情况下,所有的查询都走从库,插入/修改/删除走主库。我们通过方法名来区分操作类型(CRUD)

@Aspect
@Component
public class DataSourceAop {
?
    @Pointcut("!@annotation(com.muding.example.annotation.Master) " +
            "&& (execution(* com.muding?.example.service..*.select*(..)) " +
            "|| execution(* com.muding?.example.service..*.get*(..)))")
    public void readPointcut() {
?
    }
?
    @Pointcut("@annotation(com.muding?.example.annotation.Master) " +
            "|| execution(* com.muding?.example.service..*.insert*(..)) " +
            "|| execution(* com.muding?.example.service..*.add*(..)) " +
            "|| execution(* com.muding?.example.service..*.update*(..)) " +
            "|| execution(* com.muding?.example.service..*.edit*(..)) " +
            "|| execution(* com.muding?.example.service..*.delete*(..)) " +
            "|| execution(* com.muding?.example.service..*.remove*(..))")
    public void writePointcut() {
?
    }
?
    @Before("readPointcut()")
    public void read() {
        DBContextHolder.slave();
    }
?
    @Before("writePointcut()")
    public void write() {
        DBContextHolder.master();
    }
?
?
    /**
     * 另一种写法:if...else...  判断哪些需要读从数据库,其余的走主数据库
     */
//    @Before("execution(* com.muding?.example.service.impl.*.*(..))")
//    public void before(JoinPoint jp) {
//        String methodName = jp.getSignature().getName();
//
//        if (StringUtils.startsWithAny(methodName, "get", "select", "find")) {
//            DBContextHolder.slave();
//        }else {
//            DBContextHolder.master();
//        }
//    }
}

 

 

有一般情况就有特殊情况,特殊情况是某些情况下我们需要强制读主库,针对这种情况,我们定义一个主键,用该注解标注的就读主库

package com.muding.example.annotation;
?
public @interface Master {
}

 

 

例如,假设我们有一张表member

Service
public class MemberServiceImpl implements MemberService {
?
    @Autowired
    private MemberMapper memberMapper;
?
    @Transactional
    @Override
    public int insert(Member member) {
        return memberMapper.insert(member);
    }
?
    @Master
    @Override
    public int save(Member member) {
        return memberMapper.insert(member);
    }
?
    @Override
    public List selectAll() {
        return memberMapper.selectByExample(new MemberExample());
    }
?
    @Master
    @Override
    public String getToken(String appId) {
        //  有些读操作必须读主数据库
        //  比如,获取微信access_token,因为高峰时期主从同步可能延迟
        //  这种情况下就必须强制从主数据读
        return null;
    }
}

 

 


4.测试

@RunWith(SpringRunner.class)
@SpringBootTest
public class CjsDatasourceDemoApplicationTests {
?
    @Autowired
    private MemberService memberService;
?
    @Test
    public void testWrite() {
        Member member = new Member();
        member.setName("zhangsan");
        memberService.insert(member);
    }
    @Test
    public void testRead() {
        for (int i = 0; i < 4; i++) {
            memberService.selectAll();
        }
    }
    @Test
    public void testSave() {
        Member member = new Member();
        member.setName("muding");
        memberService.save(member);
    }
    @Test
    public void testReadFromMaster() {
        memberService.getToken("1234");
    }
}

 

 

查看控制台

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5.工程结构

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?

Spring Boot+MyBatis实现读写分离

标签:setname   str   turn   format   pack   特定   tps   ann   auto   

原文地址:https://www.cnblogs.com/d102601560/p/12933868.html

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