Spring Boot系列(三) Spring Boot 之 JDBC

数据源

类型

• javax.sql.DataSource

• javax.sql.XADataSource

• org.springframework.jdbc.datasource.embedded,EnbeddedDataSource

Spring Boot 中的数据源

单数据源(官方推荐微服务使用单数据源)

• 数据库连接池

  • Apache Commons DBCP

  • Tomcat DBCP

多数据源

实际生产中很可能会出现.

事务

• Spring 中的事务通过PlatformTransactionManagere 管理, 使用 AOP 实现, 具体实现类是 TransactionInterceptor.

• 事务传播(propagation)与保护点(savepoint): 二者密切相关.

Spring Boot 使用JDBC

单数据源

1. 配置:

spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver
spring.datasource.url=jdbc:mysql://localhost:3306/product?serverTimezone=Hongkong&useUnicode=true&characterEncoding=utf8&useSSL=false
spring.datasource.username=xlx
spring.datasource.password=xlx

注意serverTimezone的配置, 亚洲一般配置为 Hongkong.

1. 访问类注入DataSource

@Repository
public class ProductRepository {

    @Autowired
    private DataSource dataSource;
    ...
}

多数据源配置

1. 配置

spring.ds1.name=master
spring.ds1.driver-class-name=com.mysql.cj.jdbc.Driver
spring.ds1.url=jdbc:mysql://localhost:3306/product?serverTimezone=Hongkong&useUnicode=true&characterEncoding=utf8&useSSL=false
spring.ds1.username=xlx
spring.ds1.password=xlx

spring.ds2.name=slave
spring.ds2.driver-class-name=com.mysql.cj.jdbc.Driver
spring.ds2.url=jdbc:mysql://localhost:3306/product?serverTimezone=Hongkong&useUnicode=true&characterEncoding=utf8&useSSL=false
spring.ds2.username=xlx
spring.ds2.password=xlx

1. 继承 AbstractRoutingDataSource 抽象类并实现方法determineCurrentLookupKey()

这个类就是需要使用的数据源类型.

public class DynamicDataSource extends AbstractRoutingDataSource {
    @Override
    protected Object determineCurrentLookupKey() {
        return DbTypeContextHolder.get();
    }
}

查看 AbstractRoutingDataSource 的源码可以发现, 其定义了一个 Map<Object, Object> targetDataSources; 用来保存多数据源, 而上面重写的方法返回的就是需要使用的数据源的key.

public enum DBType {
    MASTER,
    SLAVE
}

1. 定义 DbTypeContextHolder 其中使用一个 ThreadLocal 来保存key, 三个方法都必不可少. 分别用来获取, 设置, 清除.

@Slf4j
public class DbTypeContextHolder {

    private final static ThreadLocal<DBType> holder = new ThreadLocal<DBType>();

    private final static ThreadLocal<Boolean> alwaysWrite = new ThreadLocal<Boolean>();

    public static DBType get() {
        if (alwaysWrite.get() != null && alwaysWrite.get()) {
            log.info("将强制使用Write");
            return DBType.MASTER;
        }
        log.info("获取到: "+holder.get().name());
        return holder.get();
    }

    public static void set(DBType dbType) {
        log.info("设置为: "+dbType.name());
        holder.set(dbType);
    }

    public static void clean() {
        log.info("清除...");
        holder.remove();
    }

    public static void setAlwaysWrite() {
        log.info("设置强制Write");
        alwaysWrite.set(true);
    }

    public static void cleanAlwaysWrite() {
        log.info("清除强制Write");
        clean();
        alwaysWrite.remove();
    }

}

1. 定义数据源配置类 MultiDataSourceConfiguration

@Configuration
public class MultiDataSourceConfiguration {

    @Autowired
    Environment environment;

    @Bean
    public DataSource getDynamicDataSource(){
        DynamicDataSource dynamicDataSource = new DynamicDataSource();
        Map<Object,Object> map = new HashMap<>();

        for (int i = 1; i < 3 ; i++) {
            String name = environment.getProperty("spring.ds"+String.valueOf(i)+".name");
            if (name==null) break;
            DataSource dataSource = DataSourceBuilder.create()
                    .driverClassName(environment.getProperty("spring.ds"+String.valueOf(i)+".driver-class-name"))
                    .username(environment.getProperty("spring.ds"+String.valueOf(i)+".username"))
                    .url(environment.getProperty("spring.ds"+String.valueOf(i)+".url"))
                    .password(environment.getProperty("spring.ds"+String.valueOf(i)+".password"))
                    .build();
            if (name.trim().toUpperCase().equals("MASTER")){
                dynamicDataSource.setDefaultTargetDataSource(dataSource);
                map.put(DBType.MASTER,dataSource);
            }else{
                map.put(DBType.SLAVE,dataSource);
            }
        }

        dynamicDataSource.setTargetDataSources(map);
        return dynamicDataSource;
    }
}

1. 检查是否可用

public Boolean save(Product product) throws SQLException {
    System.out.println("save product : "+product);
    DbTypeContextHolder.set(DBType.MASTER);
    System.out.println(dataSource.getConnection());
    DbTypeContextHolder.clean();

    DbTypeContextHolder.set(DBType.SLAVE);
    System.out.println(dataSource.getConnection());
    DbTypeContextHolder.clean();
    return true;
}

结果如下,说明是两个不同的数据源:

HikariProxyConnection@1667860231 wrapping com.mysql.cj.jdbc.ConnectionImpl@78794b01
HikariProxyConnection@556437990 wrapping com.mysql.cj.jdbc.ConnectionImpl@314c0916

1. 自动切换

可以定义切面来自动切换数据源. 比如普通的读写分离.
读写分离是通过定义在仓储层方法上的规则来实现, 同时也定义了在服务层必须使用写库来读取数据的方式.

除此之外, 如果使用 @Transactional , 因为其也是通过AOP方式实现, 所以与自动切换的AOP存在顺序关系, 为了能在 @Transactional 事务前设置好数据源, 需要增加 @Order(0) .

@Aspect
@Component
@Order(0)
public class DataSourceAspect {

    // 必须使用写库的
    @Pointcut("execution(* com.xlx.product.repository.repo..*.save*(..)) || execution(* com.xlx.product.repository.repo..*.insert*(..)) || execution(* com.xlx.product.repository.repo..*.update*(..))")
    public void write(){}

    @Before("write()")
    public void beforeWrite(JoinPoint joinPoint){
        System.out.println("beforeWrite()"+joinPoint.getSignature().getName());
        DbTypeContextHolder.set(DBType.MASTER);
    }

    @After("write()")
    public void afterWrite(JoinPoint joinPoint){
        DbTypeContextHolder.clean();
    }

    // 必须使用读库的
    @Pointcut("execution(* com.xlx.product.repository.repo..*.get*(..))|| execution(* com.xlx.product.repository.repo..*.select*(..))||execution(* com.xlx.product.repository.repo..*.count*(..))")
    public void read(){}

    @Before("read()")
    public void beforeRead(JoinPoint joinPoint){
        DbTypeContextHolder.set(DBType.SLAVE);
    }

    @After("read()")
    public void afterRead(JoinPoint joinPoint){
        DbTypeContextHolder.clean();
    }

    // 服务层有注解的方法特殊处理
    @Pointcut("@annotation(org.springframework.transaction.annotation.Transactional)" +
            "||@annotation(com.xlx.product.repository.annotation.DBTypeAnnotation)")
    public void readWrite(){}

    @Before("readWrite()")
    public void before(JoinPoint joinPoint){
        MethodSignature methodSignature = (MethodSignature)joinPoint.getSignature();
        if(methodSignature.getMethod().isAnnotationPresent(Transactional.class)) DbTypeContextHolder.set(DBType.MASTER);
        if(methodSignature.getMethod().isAnnotationPresent(DBTypeAnnotation.class)) DbTypeContextHolder.setAlwaysWrite();
    }

    @After("readWrite()")
    public void after(JoinPoint joinPoint){
        DbTypeContextHolder.clean();
        DbTypeContextHolder.cleanAlwaysWrite();
    }

}

/**
 * 放置在方法上的注解, 用来指定使用的数据源类型, 默认使用主数据源
 */
@Target({ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface DBTypeAnnotation {

    @AliasFor("values")
    DBType dbType() default DBType.MASTER;

    @AliasFor("dbType")
    DBType values() default DBType.MASTER;
}

1. service 和 controller

@Service
@Slf4j
public class ProductService {

    @Autowired
    ProductRepository repository;

    public String findAndSave(){
        log.info("findAndSave() 方法开始.....");
        String rs = testFunc();
        log.info("findAndSave() 方法结束.....");
        return rs;
    }

    @DBTypeAnnotation
    public String findAndSaveWithWrite(){
        log.info("findAndSaveWithWrite() 方法开始.....");
        String rs = testFunc();
        log.info("findAndSaveWithWrite() 方法结束.....");
        return rs;
    }

    private String testFunc() {
        List<Product> productList = repository.selectAll();
        repository.saveProduct(productList.get(0));
        productList = repository.selectAll();
        repository.saveProduct(productList.get(0));
        return "ok";
    }

}

@RestController
public class ProductController {

    @Autowired
    ProductService productService;

    @GetMapping("/product/findAndSave")
    public String findAndSave()throws SQLException {
        return productService.findAndSave();
    }

    @GetMapping("/product/findAndSaveWithWrite")
    public String findAndSaveWithWrite()throws SQLException {
        return productService.findAndSaveWithWrite();
    }
}