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<div><h1>08 WebFlux 中 Redis 实现缓存</h1>
<h3>前言</h3>
<p>首先，补充下上一篇的内容，RedisTemplate 实现操作 Redis，但操作是同步的，不是 Reactive 的。自然，支持 Reactive 的操作类为 ReactiveRedisTemplate，下面我们写个小案例。</p>
<h3>ReactiveRedisTemplate</h3>
<p>在上一篇工程中，新建 CityWebFluxReactiveController 类，路由为 /city2 开头。</p>
<pre><code>@RestController
@RequestMapping(value = &quot;/city2&quot;)
public class CityWebFluxReactiveController {
@Autowired
private ReactiveRedisTemplate reactiveRedisTemplate;
@GetMapping(value = &quot;/{id}&quot;)
public Mono&lt;City&gt; findCityById(@PathVariable(&quot;id&quot;) Long id) {
String key = &quot;city_&quot; + id;
ReactiveValueOperations&lt;String, City&gt; operations = reactiveRedisTemplate.opsForValue();
Mono&lt;City&gt; city = operations.get(key);
return city;
}
@PostMapping
public Mono&lt;City&gt; saveCity(@RequestBody City city) {
String key = &quot;city_&quot; + city.getId();
ReactiveValueOperations&lt;String, City&gt; operations = reactiveRedisTemplate.opsForValue();
return operations.getAndSet(key, city);
}
@DeleteMapping(value = &quot;/{id}&quot;)
public Mono&lt;Long&gt; deleteCity(@PathVariable(&quot;id&quot;) Long id) {
String key = &quot;city_&quot; + id;
return reactiveRedisTemplate.delete(key);
}
}
</code></pre>
<ul>
<li>写法和以前保持一致，@Autowired 注入 ReactiveRedisTemplate 对象。</li>
<li>ReactiveValueOperations 是 String（或 value）的操作视图，操作视图还有 ReactiveHashOperations、ReactiveListOperations、ReactiveSetOperations 和 ReactiveZSetOperations 等。</li>
<li>不一样的是，操作视图 set 方法是操作 City 对象，但可以 get 回 Mono 或者 Flux 对象。</li>
</ul>
<h3>结构</h3>
<p>回到这个工程，新建一个工程编写整合 Redis 实现缓存案例，工程如图：</p>
<p><img src="assets/3b4f95fda4771ca70c5bbc644f82a0c01525318.png" alt="file" /></p>
<p>目录核心如下：</p>
<ul>
<li>pom.xml maven 配置</li>
<li>application.properties 配置文件</li>
<li>domain 实体类</li>
<li>dao mongodb数据操作层</li>
<li>handler 业务层，本文要点</li>
<li>controller 控制层</li>
</ul>
<p><a href="https://github.com/JeffLi1993/springboot-learning-example">单击这里查看源代码</a>。</p>
<h3>控制层 CityWebFluxController</h3>
<p>代码如下：</p>
<pre><code>@RestController
@RequestMapping(value = &quot;/city&quot;)
public class CityWebFluxController {
@Autowired
private CityHandler cityHandler;
@GetMapping(value = &quot;/{id}&quot;)
public Mono&lt;City&gt; findCityById(@PathVariable(&quot;id&quot;) Long id) {
return cityHandler.findCityById(id);
}
@GetMapping()
public Flux&lt;City&gt; findAllCity() {
return cityHandler.findAllCity();
}
@PostMapping()
public Mono&lt;City&gt; saveCity(@RequestBody City city) {
return cityHandler.save(city);
}
@PutMapping()
public Mono&lt;City&gt; modifyCity(@RequestBody City city) {
return cityHandler.modifyCity(city);
}
@DeleteMapping(value = &quot;/{id}&quot;)
public Mono&lt;Long&gt; deleteCity(@PathVariable(&quot;id&quot;) Long id) {
return cityHandler.deleteCity(id);
}
}
</code></pre>
<h3>CityHandler 业务层</h3>
<p>目前，@Cacheable 等注解形式实现缓存没有很好的集成，二者 Mono / Flux 对象没有实现 Serializable，无法通过默认序列化器，解决方式是需要自定义序列化，这里通过手动方式与 Redis 手动集成，并实现缓存策略。</p>
<p><a href="http://coolshell.cn/articles/17416.html">参考《缓存更新的套路》</a>，缓存更新的模式有四种：Cache aside、Read through、Write through、Write behind caching。</p>
<p>这里使用的是 Cache Aside 策略，从三个维度（摘自耗子叔叔博客）：</p>
<ul>
<li>失效：应用程序先从 Cache 取数据，没有得到，则从数据库中取数据，成功后，放到缓存中。</li>
<li>命中：应用程序从 Cache 中取数据，取到后返回。</li>
<li>更新：先把数据存到数据库中，成功后，再让缓存失效。</li>
</ul>
<p>代码如下：</p>
<pre><code>@Component
public class CityHandler {
private static final Logger LOGGER = LoggerFactory.getLogger(CityHandler.class);
@Autowired
private RedisTemplate redisTemplate;
private final CityRepository cityRepository;
@Autowired
public CityHandler(CityRepository cityRepository) {
this.cityRepository = cityRepository;
}
public Mono&lt;City&gt; save(City city) {
return cityRepository.save(city);
}
public Mono&lt;City&gt; findCityById(Long id) {
// 从缓存中获取城市信息
String key = &quot;city_&quot; + id;
ValueOperations&lt;String, City&gt; operations = redisTemplate.opsForValue();
// 缓存存在
boolean hasKey = redisTemplate.hasKey(key);
if (hasKey) {
City city = operations.get(key);
LOGGER.info(&quot;CityHandler.findCityById() : 从缓存中获取了城市 &gt;&gt; &quot; + city.toString());
return Mono.create(cityMonoSink -&gt; cityMonoSink.success(city));
}
// 从 MongoDB 中获取城市信息
Mono&lt;City&gt; cityMono = cityRepository.findById(id);
if (cityMono == null)
return cityMono;
// 插入缓存
cityMono.subscribe(cityObj -&gt; {
operations.set(key, cityObj);
LOGGER.info(&quot;CityHandler.findCityById() : 城市插入缓存 &gt;&gt; &quot; + cityObj.toString());
});
return cityMono;
}
public Flux&lt;City&gt; findAllCity() {
return cityRepository.findAll().cache();
}
public Mono&lt;City&gt; modifyCity(City city) {
Mono&lt;City&gt; cityMono = cityRepository.save(city);
// 缓存存在，删除缓存
String key = &quot;city_&quot; + city.getId();
boolean hasKey = redisTemplate.hasKey(key);
if (hasKey) {
redisTemplate.delete(key);
LOGGER.info(&quot;CityHandler.modifyCity() : 从缓存中删除城市 ID &gt;&gt; &quot; + city.getId());
}
return cityMono;
}
public Mono&lt;Long&gt; deleteCity(Long id) {
cityRepository.deleteById(id);
// 缓存存在，删除缓存
String key = &quot;city_&quot; + id;
boolean hasKey = redisTemplate.hasKey(key);
if (hasKey) {
redisTemplate.delete(key);
LOGGER.info(&quot;CityHandler.deleteCity() : 从缓存中删除城市 ID &gt;&gt; &quot; + id);
}
return Mono.create(cityMonoSink -&gt; cityMonoSink.success(id));
}
}
</code></pre>
<p>首先这里注入了 RedisTemplate 对象，联想到 Spring 的 JdbcTemplate ，RedisTemplate 封装了 RedisConnection，具有连接管理，序列化和 Redis 操作等功能，还有针对 String 的支持对象 StringRedisTemplate。</p>
<p>回到更新缓存的逻辑。</p>
<p>a. findCityById 获取城市逻辑：</p>
<ul>
<li>如果缓存存在，从缓存中获取城市信息；</li>
<li>如果缓存不存在，从 DB 中获取城市信息，然后插入缓存。</li>
</ul>
<p>b. deleteCity 删除 / modifyCity 更新城市逻辑：</p>
<ul>
<li>如果缓存存在，删除；</li>
<li>如果缓存不存在，不操作。</li>
</ul>
<h3>运行工程</h3>
<p>一个操作 Redis 工程就开发完毕了，下面运行工程验证下。使用 IDEA 右侧工具栏，点击 Maven Project Tab，点击使用下 Maven 插件的 install 命令；或者使用命令行的形式，在工程根目录下，执行 Maven 清理和安装工程的指令：</p>
<pre><code>cd springboot-webflux-7-redis-cache
mvn clean install
</code></pre>
<p>在控制台中看到成功的输出：</p>
<pre><code>... 省略
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 01:30 min
[INFO] Finished at: 2018-10-15T10:00:54+08:00
[INFO] Final Memory: 31M/174M
[INFO] ------------------------------------------------------------------------
</code></pre>
<p>在 IDEA 中执行 Application 类启动，任意正常模式或者 Debug 模式，可以在控制台看到成功运行的输出：</p>
<pre><code>... 省略
2018-04-10 08:43:39.932 INFO 2052 --- [ctor-http-nio-1] r.ipc.netty.tcp.BlockingNettyContext : Started HttpServer on /0:0:0:0:0:0:0:0:8080
2018-04-10 08:43:39.935 INFO 2052 --- [ main] o.s.b.web.embedded.netty.NettyWebServer : Netty started on port(s): 8080
2018-04-10 08:43:39.960 INFO 2052 --- [ main] org.spring.springboot.Application : Started Application in 6.547 seconds (JVM running for 9.851)
</code></pre>
<p>打开 POST MAN 工具，开发必备。进行下面操作：</p>
<p><strong>新增城市信息 POST http://127.0.0.1:8080/city</strong></p>
<p><img src="assets/f69fa5b09730de686ef4837824da48e71523883-1608971278890.png" alt="file" /></p>
<p><strong>获取城市信息 GET http://127.0.0.1:8080/city/2</strong></p>
<p><img src="assets/2e129648b8e574a54ff7940f00f1dc591524819-1608971278898.png" alt="file" /></p>
<p>再请求一次，获取城市信息会发现数据获取的耗时快了很多，服务端 Console 输出的日志：</p>
<pre><code>2017-04-13 18:29:00.273 INFO 13038 --- [nio-8080-exec-1] findCityById() : 城市插入缓存 &gt;&gt; City{id=12, provinceId=3, cityName='三亚', description='水好,天蓝'}
2017-04-13 18:29:03.145 INFO 13038 --- [nio-8080-exec-2] findCityById() : 从缓存中获取了城市 &gt;&gt; City{id=12, provinceId=3, cityName='三亚', description='水好,天蓝'}
</code></pre>
<p>可见，第一次是从数据库 MongoDB 获取数据，并插入缓存，第二次直接从缓存中取。</p>
<p>更新 / 删除城市信息，这两种操作中，如果缓存有对应的数据，则删除缓存。服务端 Console 输出的日志：</p>
<pre><code>2017-04-13 18:29:52.248 INFO 13038 --- [nio-8080-exec-9] deleteCity() : 从缓存中删除城市 ID &gt;&gt; 12
</code></pre>
<h3>总结</h3>
<p>这一讲，主要补充了 Redis 对响应式的支持操作，以及缓存更新策略及实际应用小例子。</p>
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