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spring boot + mybatis如何實(shí)現(xiàn)數(shù)據(jù)庫(kù)的讀寫(xiě)分離

更新時(shí)間：2019年09月05日 09:19:17 作者：別拿豆包不當(dāng)干糧

這篇文章主要給大家介紹了關(guān)于spring boot + mybatis如何實(shí)現(xiàn)數(shù)據(jù)庫(kù)的讀寫(xiě)分離的相關(guān)資料，文中通過(guò)示例代碼介紹的非常詳細(xì)，對(duì)大家學(xué)習(xí)或者使用spring boot具有一定的參考學(xué)習(xí)價(jià)值，需要的朋友們下面來(lái)一起學(xué)習(xí)學(xué)習(xí)吧

介紹

隨著業(yè)務(wù)的發(fā)展，除了拆分業(yè)務(wù)模塊外，數(shù)據(jù)庫(kù)的讀寫(xiě)分離也是常見(jiàn)的優(yōu)化手段。

方案使用了AbstractRoutingDataSource和mybatis plugin來(lái)動(dòng)態(tài)的選擇數(shù)據(jù)源

選擇這個(gè)方案的原因主要是不需要改動(dòng)原有業(yè)務(wù)代碼，非常友好

注：

demo中使用了mybatis-plus，實(shí)際使用mybatis也是一樣的
demo中使用的數(shù)據(jù)庫(kù)是postgres，實(shí)際任一類型主從備份的數(shù)據(jù)庫(kù)示例都是一樣的
demo中使用了alibaba的druid數(shù)據(jù)源，實(shí)際其他類型的數(shù)據(jù)源也是一樣的

環(huán)境

首先，我們需要兩個(gè)數(shù)據(jù)庫(kù)實(shí)例，一為master，一為slave。

所有的寫(xiě)操作，我們?cè)趍aster節(jié)點(diǎn)上操作

所有的讀操作，我們?cè)趕lave節(jié)點(diǎn)上操作

需要注意的是：對(duì)于一次有讀有寫(xiě)的事務(wù)，事務(wù)內(nèi)的讀操作也不應(yīng)該在slave節(jié)點(diǎn)上，所有操作都應(yīng)該在master節(jié)點(diǎn)上
先跑起來(lái)兩個(gè)pg的實(shí)例，其中15432端口對(duì)應(yīng)的master節(jié)點(diǎn)，15433端口對(duì)應(yīng)的slave節(jié)點(diǎn)：

docker run \
 --name pg-master \
 -p 15432:5432 \
 --env 'PG_PASSWORD=postgres' \
 --env 'REPLICATION_MODE=master' \
 --env 'REPLICATION_USER=repluser' \
  --env 'REPLICATION_PASS=repluserpass' \
 -d sameersbn/postgresql:10-2

docker run \
 --name pg-slave \
 -p 15433:5432 \
 --link pg-master:master \
 --env 'PG_PASSWORD=postgres' \
 --env 'REPLICATION_MODE=slave' \
 --env 'REPLICATION_SSLMODE=prefer' \
 --env 'REPLICATION_HOST=master' \
 --env 'REPLICATION_PORT=5432' \
 --env 'REPLICATION_USER=repluser' \
  --env 'REPLICATION_PASS=repluserpass' \
 -d sameersbn/postgresql:10-2

實(shí)現(xiàn)

整個(gè)實(shí)現(xiàn)主要有3個(gè)部分：

配置兩個(gè)數(shù)據(jù)源
實(shí)現(xiàn)AbstractRoutingDataSource來(lái)動(dòng)態(tài)的使用數(shù)據(jù)源
實(shí)現(xiàn)mybatis plugin來(lái)動(dòng)態(tài)的選擇數(shù)據(jù)源

配置數(shù)據(jù)源

將數(shù)據(jù)庫(kù)連接信息配置到application.yml文件中

spring:
 mvc:
  servlet:
   path: /api

datasource:
 write:
  driver-class-name: org.postgresql.Driver
  url: "${DB_URL_WRITE:jdbc:postgresql://localhost:15432/postgres}"
  username: "${DB_USERNAME_WRITE:postgres}"
  password: "${DB_PASSWORD_WRITE:postgres}"
 read:
  driver-class-name: org.postgresql.Driver
  url: "${DB_URL_READ:jdbc:postgresql://localhost:15433/postgres}"
  username: "${DB_USERNAME_READ:postgres}"
  password: "${DB_PASSWORD_READ:postgres}"


mybatis-plus:
 configuration:
  map-underscore-to-camel-case: true

write寫(xiě)數(shù)據(jù)源，對(duì)應(yīng)到master節(jié)點(diǎn)的15432端口

read讀數(shù)據(jù)源，對(duì)應(yīng)到slave節(jié)點(diǎn)的15433端口

將兩個(gè)數(shù)據(jù)源信息注入為DataSourceProperties：

@Configuration
public class DataSourcePropertiesConfig {

  @Primary
  @Bean("writeDataSourceProperties")
  @ConfigurationProperties("datasource.write")
  public DataSourceProperties writeDataSourceProperties() {
    return new DataSourceProperties();
  }

  @Bean("readDataSourceProperties")
  @ConfigurationProperties("datasource.read")
  public DataSourceProperties readDataSourceProperties() {
    return new DataSourceProperties();
  }
}

實(shí)現(xiàn)AbstractRoutingDataSource

spring提供了AbstractRoutingDataSource，提供了動(dòng)態(tài)選擇數(shù)據(jù)源的功能，替換原有的單一數(shù)據(jù)源后，即可實(shí)現(xiàn)讀寫(xiě)分離:

@Component
public class CustomRoutingDataSource extends AbstractRoutingDataSource {

  @Resource(name = "writeDataSourceProperties")
  private DataSourceProperties writeProperties;

  @Resource(name = "readDataSourceProperties")
  private DataSourceProperties readProperties;


  @Override
  public void afterPropertiesSet() {
    DataSource writeDataSource = 
      writeProperties.initializeDataSourceBuilder().type(DruidDataSource.class).build();
    DataSource readDataSource = 
      readProperties.initializeDataSourceBuilder().type(DruidDataSource.class).build();
    
    setDefaultTargetDataSource(writeDataSource);

    Map<Object, Object> dataSourceMap = new HashMap<>();
    dataSourceMap.put(WRITE_DATASOURCE, writeDataSource);
    dataSourceMap.put(READ_DATASOURCE, readDataSource);
    setTargetDataSources(dataSourceMap);

    super.afterPropertiesSet();
  }

  @Override
  protected Object determineCurrentLookupKey() {
    String key = DataSourceHolder.getDataSource();

    if (key == null) {
       // default datasource
      return WRITE_DATASOURCE;
    }

    return key;
  }

}

AbstractRoutingDataSource內(nèi)部維護(hù)了一個(gè)Map<Object, Object>的Map

在初始化過(guò)程中，我們將write、read兩個(gè)數(shù)據(jù)源加入到這個(gè)map

調(diào)用數(shù)據(jù)源時(shí)：determineCurrentLookupKey()方法返回了需要使用的數(shù)據(jù)源對(duì)應(yīng)的key

當(dāng)前線程需要使用的數(shù)據(jù)源對(duì)應(yīng)的key，是在DataSourceHolder類中維護(hù)的：

public class DataSourceHolder {

  public static final String WRITE_DATASOURCE = "write";
  public static final String READ_DATASOURCE = "read";

  private static final ThreadLocal<String> local = new ThreadLocal<>();


  public static void putDataSource(String dataSource) {
    local.set(dataSource);
  }

  public static String getDataSource() {
    return local.get();
  }

  public static void clearDataSource() {
    local.remove();
  }

}

實(shí)現(xiàn)mybatis plugin

上面提到了當(dāng)前線程使用的數(shù)據(jù)源對(duì)應(yīng)的key，這個(gè)key需要在mybatis plugin根據(jù)sql類型來(lái)確定
MybatisDataSourceInterceptor類：

@Component
@Intercepts({
    @Signature(type = Executor.class, method = "update",
        args = {MappedStatement.class, Object.class}),
    @Signature(type = Executor.class, method = "query",
        args = {MappedStatement.class, Object.class, RowBounds.class, ResultHandler.class}),
    @Signature(type = Executor.class, method = "query",
        args = {MappedStatement.class, Object.class, RowBounds.class, ResultHandler.class,
            CacheKey.class, BoundSql.class})})
public class MybatisDataSourceInterceptor implements Interceptor {

  @Override
  public Object intercept(Invocation invocation) throws Throwable {

    boolean synchronizationActive = TransactionSynchronizationManager.isSynchronizationActive();
    if(!synchronizationActive) {
      Object[] objects = invocation.getArgs();
      MappedStatement ms = (MappedStatement) objects[0];

      if (ms.getSqlCommandType().equals(SqlCommandType.SELECT)) {
        DataSourceHolder.putDataSource(DataSourceHolder.READ_DATASOURCE);
      }
    }

    return invocation.proceed();
  }

  @Override
  public Object plugin(Object target) {
    return Plugin.wrap(target, this);
  }

  @Override
  public void setProperties(Properties properties) {
  }
}

僅當(dāng)未在事務(wù)中，并且調(diào)用的sql是select類型時(shí)，在DataSourceHolder中將數(shù)據(jù)源設(shè)為read

其他情況下，AbstractRoutingDataSource會(huì)使用默認(rèn)的write數(shù)據(jù)源

至此，項(xiàng)目已經(jīng)可以自動(dòng)的在讀、寫(xiě)數(shù)據(jù)源間切換，無(wú)需修改原有的業(yè)務(wù)代碼

最后，提供demo使用依賴版本

<parent>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-parent</artifactId>
  <version>2.1.7.RELEASE</version>
  <relativePath/> <!-- lookup parent from repository -->
</parent>

<dependencies>
  <dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter</artifactId>
  </dependency>
  <dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
  </dependency>

  <dependency>
    <groupId>org.postgresql</groupId>
    <artifactId>postgresql</artifactId>
    <version>42.2.2</version>
  </dependency>
  <dependency>
    <groupId>com.alibaba</groupId>
    <artifactId>druid-spring-boot-starter</artifactId>
    <version>1.1.9</version>
  </dependency>
  <dependency>
    <groupId>com.baomidou</groupId>
    <artifactId>mybatisplus-spring-boot-starter</artifactId>
    <version>1.0.5</version>
  </dependency>
  <dependency>
    <groupId>com.baomidou</groupId>
    <artifactId>mybatis-plus</artifactId>
    <version>2.1.9</version>
  </dependency>
  <dependency>
    <groupId>io.springfox</groupId>
    <artifactId>springfox-swagger2</artifactId>
    <version>2.8.0</version>
  </dependency>
  <dependency>
    <groupId>io.springfox</groupId>
    <artifactId>springfox-swagger-ui</artifactId>
    <version>2.8.0</version>
  </dependency>
  <dependency>
    <groupId>org.projectlombok</groupId>
    <artifactId>lombok</artifactId>
    <version>1.16.20</version>
  </dependency>

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

總結(jié)

以上就是這篇文章的全部?jī)?nèi)容了，希望本文的內(nèi)容對(duì)大家的學(xué)習(xí)或者工作具有一定的參考學(xué)習(xí)價(jià)值，謝謝大家對(duì)腳本之家的支持。

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