Spring Data Redis 如何将 RedisTemplate 注入为 ListOperations 类型

技术交流
1

Spring Data Redis 如何将 RedisTemplate 注入为 ListOperations 类型

在 Spring Data Redis 官方文档中，可以看到这样一个常规用法：

<?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:p="http://www.springframework.org/schema/p"
  xsi:schemaLocation="http://www.springframework.org/schema/beans https://www.springframework.org/schema/beans/spring-beans.xsd">

  <bean id="jedisConnectionFactory" class="org.springframework.data.redis.connection.jedis.JedisConnectionFactory" p:use-pool="true"/>

  <bean id="stringRedisTemplate" class="org.springframework.data.redis.core.StringRedisTemplate" p:connection-factory-ref="jedisConnectionFactory"/>
  ...
</beans>

public class Example {

  @Autowired
  private StringRedisTemplate redisTemplate;

  public void addLink(String userId, URL url) {
    redisTemplate.opsForList().leftPush(userId, url.toExternalForm());
  }
}

代码摘自：Spring Data Redis :: Spring Data Redis

RedisTemplate 和 ListOperations 并没有继承关系，这里是怎么将 RedisTemplate 注入到 ListOperations 类型上去的呢？而且不但可以将 RedisTemplate 注入到 ListOperations ，也可以注入到 ValueOperations、SetOperations、ZSetOperations、HashOperations 等类型上。

PropertyEditor

Spring 框架可以通过 java.beans.PropertyEditor 接口的实现类来实现类型转换。

Spring Data Redis 提供了 ListOperationsEditor 可以将 RedisTemplate 转为 ListOperations：

import java.beans.PropertyEditorSupport;

/**
 * PropertyEditor allowing for easy injection of {@link ListOperations} from {@link RedisOperations}.
 *
 * @author Costin Leau
 */
class ListOperationsEditor extends PropertyEditorSupport {

	public void setValue(Object value) {
		if (value instanceof RedisOperations) {
			super.setValue(((RedisOperations) value).opsForList());
		} else {
			throw new IllegalArgumentException("Editor supports only conversion of type " + RedisOperations.class);
		}
	}
}

以上代码中，RedisOperations 是 RedisTemplate 的父级接口，((RedisOperations) value).opsForList() 实际上就是调用 RedisTemplate.opsForList() 获取 ListOperations。

Spring 如何注册 PropertyEditor

Note also that the standard JavaBeans infrastructure automatically discovers PropertyEditor classes (without you having to register them explicitly) if they are in the same package as the class they handle and have the same name as that class, with Editor appended. For example, one could have the following class and package structure, which would be sufficient for the SomethingEditor class to be recognized and used as the PropertyEditor for Something-typed properties.

文档中提到，如果 PropertyEditor 类与它们处理的类在同一个包中，并且类名再加上 Editor 后缀，则无需显式注册，该 PropertyEditor 可以被自动发现。

在 Spring Data Redis 源码中可以看到，ListOperations 类和 ListOperationsEditor 都在 org.springframework.data.redis.core 包下，且 ListOperationsEditor 符合命名规则，即在 ListOperations 类名上加上 Editor 后缀，所以可以自动发现并生效。

原文：马士兵微信公众号