响应式编程基础教程：Spring Boot 与 R2DBC 整合

R2DBC 是 "Reactive Relational Database Connectivity"的简称。
R2DBC 是一个 API 规范的倡议，声明对于访问关系型数据库驱动实现了一些响应式的API。

R2DBC的诞生为了非阻塞的应用栈， 使用很少的线程可以处理大量的并发同时减少硬件资源。大量的应用还是使用的关系型数据库，然而很多 NoSQL 数据提供了响应式客户端，并不是所有的项目都适合迁移到 NoSQL。因此，R2DBC 应运而生。

R2DBC 特点

• 对于 R2DBC 的驱动实例，Spring 支持基于Java 的@Connfiguration的配置
• R2dbcEntityTemplate 作为实体绑定的核心操作类
• 整合了Spring Conversion Service 丰富的对象映射
• 基于注解元数据映射关系
• 自动实现 Reposity 接口，包含支持自定义的查询方法

R2DBC 使用

接下来通过一个官方的实例来演示

依赖 pom.xml

<dependencies>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-data-r2dbc</artifactId>
		</dependency>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-webflux</artifactId>
		</dependency>

		<dependency>
			<groupId>com.h2database</groupId>
			<artifactId>h2</artifactId>
		</dependency>
		<dependency>
			<groupId>io.r2dbc</groupId>
			<artifactId>r2dbc-h2</artifactId>
		</dependency>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-test</artifactId>
			<scope>test</scope>
		</dependency>
		<dependency>
			<groupId>io.projectreactor</groupId>
			<artifactId>reactor-test</artifactId>
		</dependency>
		<dependency>
			<groupId>org.projectlombok</groupId>
			<artifactId>lombok</artifactId>
			<optional>true</optional>
		</dependency>
	</dependencies>

定义 Person 实体

public class Person {
  
    private final String id;
    private final String name;
    private final int age;

    public Person(String id, String name, int age) {
        this.id = id;
        this.name = name;
        this.age = age;
    }

    public String getId() {
        return id;
    }

    public String getName() {
        return name;
    }

    public int getAge() {
        return age;
    }

    @Override
    public String toString() {
        return "Person [id=" + id + ", name=" + name + ", age=" + age + "]";
    }
}

测试

import com.example.springreactivedemo.model.Person;
import io.r2dbc.spi.ConnectionFactories;
import io.r2dbc.spi.ConnectionFactory;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.springframework.data.r2dbc.core.R2dbcEntityTemplate;
import reactor.test.StepVerifier;

public class Test1 {

    private static final Log log = LogFactory.getLog(Test1.class);

    public static void main(String[] args) {
        ConnectionFactory connectionFactory = ConnectionFactories.get("r2dbc:h2:mem:///test?options=DB_CLOSE_DELAY=-1;DB_CLOSE_ON_EXIT=FALSE");


        R2dbcEntityTemplate template = new R2dbcEntityTemplate(connectionFactory);

        template.getDatabaseClient().sql("CREATE TABLE person" +
                        "(id VARCHAR(255) PRIMARY KEY," +
                        "name VARCHAR(255)," +
                        "age INT)")
                .fetch()
                .rowsUpdated()
                .as(StepVerifier::create)
                .expectNextCount(1)
                .verifyComplete();

        template.insert(Person.class)
                .using(new Person("joe", "Joe", 34))
                .as(StepVerifier::create)
                .expectNextCount(1)
                .verifyComplete();

        template.select(Person.class)
                .first()
                .doOnNext(it -> log.info(it))
                .as(StepVerifier::create)
                .expectNextCount(1)
                .verifyComplete();
    }
}

运行结果：

15:34:40.101 [main] DEBUG org.springframework.r2dbc.core.DefaultDatabaseClient - Executing SQL statement [INSERT INTO person (id, name, age) VALUES ($1, $2, $3)]
15:34:40.103 [main] DEBUG io.r2dbc.h2.client.SessionClient - Request:  INSERT INTO person (id, name, age) VALUES ($1, $2, $3) {1: 'joe', 2: 'Joe', 3: 34}
Exception in thread "main" java.lang.AssertionError: expectation "expectNextCount(1)" failed (expected: count = 1; actual: counted = 0; signal: onError(java.lang.IllegalStateException: Required identifier property not found for class com.example.springreactivedemo.model.Person!))
	at reactor.test.MessageFormatter.assertionError(MessageFormatter.java:115)
	at reactor.test.MessageFormatter.failPrefix(MessageFormatter.java:104)
	at reactor.test.MessageFormatter.fail(MessageFormatter.java:73)
	at reactor.test.MessageFormatter.failOptional(MessageFormatter.java:88)

通过运行官方文档的实例出现了以上的报错信息，我们来看一下错误信息，Required identifier property not found for class com.example.springreactivedemo.model.Person! ， Person 要求一个唯一属性，将 Person 类 id 增加了注解@Id ， 再次执行成功，日志如下。

15:38:06.806 [main] DEBUG org.springframework.r2dbc.core.DefaultDatabaseClient - Executing SQL statement [INSERT INTO person (id, name, age) VALUES ($1, $2, $3)]
15:38:06.808 [main] DEBUG io.r2dbc.h2.client.SessionClient - Request:  INSERT INTO person (id, name, age) VALUES ($1, $2, $3) {1: 'joe', 2: 'Joe', 3: 34}
15:38:06.847 [main] DEBUG io.r2dbc.h2.client.SessionClient - Request:  CALL H2VERSION()
15:38:06.847 [main] DEBUG io.r2dbc.h2.client.SessionClient - Response: org.h2.result.LocalResultImpl@72c927f1 columns: 1 rows: 1 pos: -1
15:38:06.847 [main] DEBUG org.springframework.r2dbc.core.DefaultDatabaseClient - Executing SQL statement [SELECT person.* FROM person LIMIT 1]
15:38:06.853 [main] DEBUG io.r2dbc.h2.client.SessionClient - Request:  SELECT person.* FROM person LIMIT 1
15:38:06.854 [main] DEBUG io.r2dbc.h2.client.SessionClient - Response: org.h2.result.LocalResultImpl@1c32886a columns: 3 rows: 1 pos: -1
15:38:06.876 [main] INFO com.example.springreactivedemo.client.Test1 - Person [id=joe, name=Joe, age=34]

Spring Boot 整合 R2DBC 流程

1. 创建 ConnectionFactory 和 R2dbcEntityTemplate

@Configuration
public class ApplicationConfiguration extends AbstractR2dbcConfiguration {

    @Override
    @Bean
    public ConnectionFactory connectionFactory() {
        return new H2ConnectionFactory(H2ConnectionConfiguration.builder()
                .url("r2dbc:h2:mem:///test?options=DB_CLOSE_DELAY=-1;DB_CLOSE_ON_EXIT=FALSE")
                .build());
    }

    @Bean
    public R2dbcEntityTemplate r2dbcEntityTemplate() {
        return new R2dbcEntityTemplate(connectionFactory());
    }
}

2. CRUD 使用

@RestController
@Slf4j
public class PersonController {

    private R2dbcEntityTemplate r2dbcEntityTemplate;

    public PersonController(R2dbcEntityTemplate r2dbcEntityTemplate) {
        this.r2dbcEntityTemplate = r2dbcEntityTemplate;
        // 创建表结构
        r2dbcEntityTemplate.getDatabaseClient().sql("drop table person if exists; CREATE TABLE person" +
                "(id VARCHAR(255) PRIMARY KEY," +
                "name VARCHAR(255)," +
                "age INT)").fetch().rowsUpdated().subscribe();
    }

    @PostMapping("/save")
    public Mono<Person> insert(@RequestBody Person person) {
        return r2dbcEntityTemplate.insert(Person.class).using(person);
    }

    @GetMapping("/list")
    public Flux<Person> list() {
        return r2dbcEntityTemplate.select(Query.empty(), Person.class);
    }

    @PutMapping("/update")
    public void update(@RequestBody Person person) {
        r2dbcEntityTemplate.update(Person.class)
                .inTable("person") //可以指定 table
                .matching(Query.query(Criteria.where("id").is(person.getId())))
                .apply(Update.update("name", person.getName())).subscribe();
    }

    @DeleteMapping("/delete")
    public Mono<Integer> delete(@RequestBody Person person) {
        return r2dbcEntityTemplate.delete(Person.class).matching(Query.query(Criteria.where("id").is(person.getId()))).all();
    }
}

总结

Spring Boot 整合 R2DBC 简单实例使用完成，需要注意的是响应式编程和之前命令式编程有很大的区别，在写update方法中，在 R2dbcEntityTemplate 执行 update 最后没有调用 subscribe，导致 update 方法没有执行，在响应式编程中定义的方法流程需要通过触发才会执行。代码里面使用 subscribe 的方式来触发调用，还可以将执行 update返回的值 Mono<Integer>，这样也会触发执行。

参考：

https://docs.spring.io/spring-data/r2dbc/docs/current/reference/html/#introduction