統一緩存帝國 - 實戰 Spring Cache

{"type":"doc","content":[{"type":"heading","attrs":{"align":null,"level":2}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/f9/f918988d09de7224ff57b675c0719292.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"前三篇講解的緩存使用和分佈式鎖的都是基於 Redis 來做緩存的，本篇我來向大家介紹一種兼容所有緩存中間件的方案，不論我們是使用 Redis 還是 Ehcache，都不需要關心如何操作 Redis 或者 Ehcache，這套方案統統幫你搞定。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"這套方案就是大名鼎鼎的 ","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"Spring 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APP，進入到了秒殺商品的詳情頁，那這個商品數據我們會先去數據庫查詢，然後返回給客戶端。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"2.因爲有大量用戶短時間內進入到了詳情頁，所以可以把活動列表緩存起來，直接讀緩存就可以了。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"3.那下次再查詢商品時，直接去緩存查詢就可以了。如果秒殺商品下架了，緩存的數據不會用到了，就把緩存刪掉就可以了。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"4.上面幾步看起來也沒啥問題，但是放緩存，刪除緩存這兩步是需要我們去手動寫代碼實現的。有沒有一種方式不用寫操作緩存的代碼？","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"5.假如現在用的緩存中間件是 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來做了，是不是很爽，再也不用自己去寫緩存操作的邏輯了。","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":3},"content":[{"type":"text","text":"1.5 緩存註解","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"Spring 提供了四個註解來聲明緩存規則。@Cacheable，@CachePut，@CacheEvict，@Caching。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/b6/b62429adfd5a48290f8b3d44aee37a19.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"大家先有個概念，後面我們再來看怎麼使用這些緩存註解。","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"二、使用緩存","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":3},"content":[{"type":"text","text":"2.1 引入 Spring Cache 依賴","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"在 pom 文件中引入 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如下所示：","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/6b/6b9de1e856fbd3e3e4a83caf1ae8cc69.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"當然，別忘了還要在 pom 文件中 引入 Redis 的依賴，不然用不了 Redis。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"xml"},"content":[{"type":"text","text":"\n org.springframework.boot\n spring-boot-starter-data-redis\n\n","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":3},"content":[{"type":"text","text":"2.3 測試緩存","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"那基礎的配置已經做好了，現在就是看怎麼使用 Spring Cache 了。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"（1）啓動類上添加 ","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"@EnableCaching","attrs":{}}],"attrs":{}},{"type":"text","text":"註解。本文案例就是在 啓動類 PassjavaQuestionApplication 添加 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參數。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"下面的代碼出於演示作用，用了最簡單的邏輯，test 方法直接返回一個數字，連數據庫查詢都沒有做。不過沒關係，我們主要驗證 Spring Cache 是否對方法的結果進行了緩存。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"java"},"content":[{"type":"text","text":"@RequestMapping(\"/test\")\n@Cacheable({\"hot\"})\npublic int test() {\n return 222;\n}\n","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"大家注意，@Cacheable 註解中小括號裏面還含有大括號，大括號裏面還有 “hot” 字符串，這個 hot 字符串你可以把它當作一個緩存的名字，然後將 test 方法返回的結果存到 hot 緩存中。我們也可以用 value=\"hot\" 的方式。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"第一次調用 test 方法前，既沒有 hot 緩存，更沒有 test 的結果緩存。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"調用 test 方法後，Redis 中就創建出了 hot 緩存了，然後緩存了一個 key，如下圖所示：","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/b3/b331d654454460114636bc56029ccf57.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"第二次調用 test 方法時，就從緩存 hot 中將 test 方法緩存的結果 222 取出來了，爲了驗證沒有執行 test 中的方法，大家可以在 test 方法中打下 log 或者斷點。最後的驗證結果肯定是沒有走 test 方法的，而是直接從緩存中獲取的。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"那我們再來測試一個方法，方法名改爲 test2，且請求路徑也改爲 test2 了。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"java"},"content":[{"type":"text","text":"@RequestMapping(\"/test2\")\n@Cacheable({\"hot\"})\npublic int test2() {\n return 456;\n}\n","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong","attrs":{}}],"text":"大家覺得這兩個方法的結果都會緩存嗎？還是隻會緩存第一個被調用的方法。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"經過測試，執行第一個 test 方法後，再執行 test2 方法，緩存結果一直是 222 不會變。因爲他們的 key 都是 默認的 SimpleKey[]，所以兩個方法對應的緩存的 key 都叫這個，所以得到的緩存值是一樣的。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"（3）加上數據庫查詢的測試。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"有的同學可能覺得上面的測試太簡單了，test 方法裏面啥都沒做，還緩存啥呢，完全沒必要啊。沒關係，大家的顧慮是對的，我們來加上數據庫查詢，安排~","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"先說下場景：前端需要查詢某個題目的詳情，正常邏輯是查詢數據庫後返回結果。假定這個查詢操作非常頻繁，我們需要將題目詳情進行緩存。我們先看看常規 Redis 緩存方案：","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"先從 Redis 緩存中查看緩存中是否有該題目，如果緩存中有，則返回緩存中的題目；如果沒有，就從數據庫中查。查詢出題目後，就用 Redis 存起來，然後返回。這裏就要寫操作 Redis 的代碼了：查詢 Redis 緩存、更新 Redis 緩存。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"java"},"content":[{"type":"text","text":"// 查詢緩存，假定該題目詳情緩存的 key=question1\nredisTemplate.opsForValue().get(\"question1\"); \n// 更新緩存\nredisTemplate.opsForValue().set(\"question1\", questionEntity);\n","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"那如果用 Spring Cache 註解的話，上面兩行代碼可以直接幹掉了。如下所示，加一個 @Cacheable 註解搞定。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"java"},"content":[{"type":"text","text":"@Cacheable({\"question\", \"hot\"})\npublic QuestionEntity info(Long id) {\n return getById(id); // 查詢數據庫操作\n}\n","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"其中 question 和 hot 是緩存的名字，我們可以將結果放到不同的緩存中。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"結論：","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"bulletedlist","content":[{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"如果沒有指定請求參數，則緩存生成的 key name，是默認自動生成的，叫做 SimpleKey[]。","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"如果指定了請求參數，則緩存的 key name 就是請求參數，比如上面 info 方法，key 等於我傳入的 id = 1。","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"緩存中 key 對應的 value 默認使用 JDK 序列化後的數據。","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"value 的過期時間爲 -1，表示永不過期。","attrs":{}}]}]}],"attrs":{}},{"type":"heading","attrs":{"align":null,"level":3},"content":[{"type":"text","text":"2.4 自定義配置類","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"上面保存的緩存數據都是默認設置，我們也可以自己定義配置，如下所示，在配置文件 application.properties 添加如下配置：","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"text"},"content":[{"type":"text","text":"# 使用 Redis 作爲緩存組件\nspring.cache.type=redis\n# 緩存過期時間爲 3600s\nspring.cache.redis.time-to-live=3600000\n# 緩存的鍵的名字前綴\nspring.cache.redis.key-prefix=passjava_\n# 是否使用緩存前綴\nspring.cache.redis.use-key-prefix=true\n# 是否緩存控制，防止緩存穿透\nspring.cache.redis.cache-null-values=true\n","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"然後需要加一個配置類：MyCacheConfig。可以在我的開源項目 passjava 獲取完整源碼。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"java"},"content":[{"type":"text","text":"RedisCacheConfiguration redisCacheConfiguration(CacheProperties cacheProperties) {\n}\n","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":3},"content":[{"type":"text","text":"2.5 自定義 key","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"然後我們可以指定 key 的值，可以在 @Cacheable 註解裏面加上 key 的值 ","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"#root.method.name","attrs":{}}],"attrs":{}},{"type":"text","text":"。這是一種特有的表達式，稱作 ","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"SpEL","attrs":{}}],"attrs":{}},{"type":"text","text":" 表達式，這裏代表用方法名作爲緩存 key 的名字。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"java"},"content":[{"type":"text","text":"@Cacheable(value = {\"hot\"}, key = \"#root.method.name\")\n","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"接下來就是見證奇蹟的時刻，調用 test 方法和 test2 方法，發現有兩個不同的 key，一個是 passjava_test1，另外一個 passjava_test2，它們的 key 就是前綴 passjava_ + 方法名 組成。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/b7/b7c03e53ff88246d5c46a6ac4ec1cb6f.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"SpEL 表達式還有很多其它規則，如下所示：","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/a4/a4901477e8962b8e2778e7225c3a8ec3.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"可以根據項目需要選擇合適的表達式來自定義 key。","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":3},"content":[{"type":"text","text":"2.6 自定義條件","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"除了設置緩存條目的 key，我們還可以自定義條件來決定是否將緩存功能關閉。這裏就要用到@Cacheable 另外兩個屬性：condition 和 unless，它倆的格式還是用 SpEL 表達式。對應的四個屬性總結如下：","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/93/93e92a0fdddc566724f8e630eed206a8.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"代碼示例如下：","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"java"},"content":[{"type":"text","text":"@Cacheable(value = \"hot\", unless = \"#result.message.containss('NoCache')\")\n","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"當放回的結果 message 字段包含有 NoCache 就不會進行緩存。","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":3},"content":[{"type":"text","text":"2.7 更新註解","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"@CachePut 也是用來更新緩存，和 @Cacheable 非常相似，不同點是 @CachePut 註解的方法始終都會執行，返回值也會也會放到緩存中。通常用在保存的方法上。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"保存成功後，可以將 key 設置保存實例的 id。這個怎麼做呢？","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"之前我們說過 key 可以通過 SpEL 表達式來指定，這裏就可以搭配 #result.id 來實現。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"這裏還是用個例子來說明用法：創建題目的方法，返回題目實例，其中包含有題目 id。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"java"},"content":[{"type":"text","text":"@RequestMapping(\"/create\")\n@CachePut(value = \"hot\", key = \"#result.id\")\npublic QuestionEntity create(@Valid @RequestBody QuestionEntity question){\n return IQuestionService.createQuestion(question);\n}\n","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"保存的 id 是自增的，值爲 123，所以緩存中的 key = passjava_123。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/b3/b3c03ba74c61b6a1dcde83f3917c5e07.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"heading","attrs":{"align":null,"level":3},"content":[{"type":"text","text":"2.8 刪除緩存註解","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"@CacheEvict 註解的方法在調用時不會在緩存中添加任何東西，但是會從從緩存中移除之前的緩存結果。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"示例代碼如下：","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"java"},"content":[{"type":"text","text":"@RequestMapping(\"/remove/{id}\")\n@CacheEvict(value = \"hot\")\npublic R remove(@PathVariable(\"id\") Long id){\n IQuestionService.removeById(id);\n return R.ok();\n}\n","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"刪除條目的 key 與傳遞進來的 id 相同。我測試的時候傳的 id = 123，經過前綴passjava_組裝後就是 passjava_123，所以將之前緩存的 passjava_123 刪除了。重複執行也不會報錯。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"注意：@CacheEvict 和 @Cacheable、@CachePut 不同，它能夠應用在返回值爲 void 的方法上。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"@CacheEvict 還有些屬性可供使用，總結如下：","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/ac/acb19c366113dbac31ad45d80ad27f16.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"三、 總結","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"本文通過傳統使用緩存的方式的痛點引出 Spring 框架中的 Cache 組件。然後詳細介紹了 Spring Cache 組件的用法：","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"bulletedlist","content":[{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"五大註解。 @Cacheable、@CachePut、@CacheEvict、@Caching,、@CacheConfig。","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"如何自定義緩存條目的 key。","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"如何自定義 Cache 配置。","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"如何自定義緩存的條件。","attrs":{}}]}]}],"attrs":{}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"參考資料：","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"www.passjava.cn","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"Spring in Action","attrs":{}}]}]}