# SpringBoot2核心技术与响应式编程

**Repository Path**: orehapeinn/springboot2

## Basic Information

- **Project Name**: SpringBoot2核心技术与响应式编程
- **Description**: SpringBoot2核心技术与响应式编程
- **Primary Language**: Java
- **License**: Not specified
- **Default Branch**: master
- **Homepage**: None
- **GVP Project**: No

## Statistics

- **Stars**: 0
- **Forks**: 1202
- **Created**: 2021-02-17
- **Last Updated**: 2021-06-03

## Categories & Tags

**Categories**: Uncategorized

**Tags**: None

## README

# SpringBoot2核心技术与响应式编程

[前面几张笔记链接](https://gitee.com/orehapeinn/springboot2.git) 

[视频链接](https://www.bilibili.com/video/BV19K4y1L7MT)





## Spring整合篇

### spring cache

Spring cache 是一种基于注解的可以对某些方法做缓存(主要可以用在dao层方法),可以用来减少数据库压力,spring cache并不提供缓存实现,而是对缓存使用地抽象,支持本地缓存,Redis缓存等.

#### 核心注解

- @Cachable  查询方法

  每次调用指定方法前会从缓存中检查指定的数据是否在缓存中,如果存在,直接返回缓存中的数据,不再指定该方法.否则指定该方法获取到结果放入缓存中后返回

  注解属性 String key()

  > Spring Expression Language (SpEL) expression for computing the key dynamically.
  > Default is "", meaning all method parameters are considered as a key, unless a custom keyGenerator has been configured.
  > The SpEL expression evaluates against a dedicated context that provides the following meta-data:
  > #root.method, #root.target, and #root.caches for references to the method, target object, and affected cache(s) respectively.
  > Shortcuts for the method name (#root.methodName) and target class (#root.targetClass) are also available.
  > Method arguments can be accessed by index. For instance the second argument can be accessed via #root.args[1], #p1 or #a1. Arguments can also be accessed by name if that information is available.

    String keyGenerator()  可以自定义key生成器,与以上的key互斥,两者不可并存,可以往容器中注入自定义keyGenerator填入它的beanName就可以让spring使用自定的key生成策略

  ```java
  @Bean
  public KeyGenerator keyGenerator() {
    // return new SimpleKeyGenerator();  //spring提供的简单的KeyGenerator
    return (target, method, params) ->
      target.getClass().getSimpleName() + method.getName()
      + "[" + StringUtils.arrayToCommaDelimitedString(params) + "]";
  }
  // user::$Proxy61selectByIdAndName[2,郑思淼], 这个获取到的 target 是一个代理类,也合理,因为我们用的是mybatis
  ```

  

  > The bean name of the custom org.springframework.cache.interceptor.KeyGenerator to use.
  > Mutually exclusive with the key attribute.
  > See Also:
  > CacheConfig.keyGenerator

- CachePut 修改方法

  每次调用指定方法都会执行,并将结果存入缓存

- CacheEvict  删除或修改
  boolean beforeInvocation() default false; 方法执行前还是执行后进行缓存驱逐 默认方法执行后

  指定方法执行之前或后会清除对应的缓存

核心执行逻辑

```java
// CacheInteceptor.invoke   -> CacheAspectSupport.execute()
private Object execute(final CacheOperationInvoker invoker, Method method, CacheOperationContexts contexts) {
		// Special handling of synchronized invocation
		if (contexts.isSynchronized()) {
			CacheOperationContext context = contexts.get(CacheableOperation.class).iterator().next();
			if (isConditionPassing(context, CacheOperationExpressionEvaluator.NO_RESULT)) {
				Object key = generateKey(context, CacheOperationExpressionEvaluator.NO_RESULT);
				Cache cache = context.getCaches().iterator().next();
				try {
					return wrapCacheValue(method, handleSynchronizedGet(invoker, key, cache));
				}
				catch (Cache.ValueRetrievalException ex) {
					// Directly propagate ThrowableWrapper from the invoker,
					// or potentially also an IllegalArgumentException etc.
					ReflectionUtils.rethrowRuntimeException(ex.getCause());
				}
			}
			else {
				// No caching required, only call the underlying method
				return invokeOperation(invoker);
			}
		}


		// Process any early evictions 是否先删除缓存
		processCacheEvicts(contexts.get(CacheEvictOperation.class), true,
				CacheOperationExpressionEvaluator.NO_RESULT);

		// Check if we have a cached item matching the conditions
		Cache.ValueWrapper cacheHit = findCachedItem(contexts.get(CacheableOperation.class));

		// Collect puts from any @Cacheable miss, if no cached item is found
  	// 如果有 上面 @Cachable 缓存没有命中,再来处理 @CachePut注解,这里只进行预处理,没有实质查询
		List<CachePutRequest> cachePutRequests = new ArrayList<>();
		if (cacheHit == null) {
			collectPutRequests(contexts.get(CacheableOperation.class),
					CacheOperationExpressionEvaluator.NO_RESULT, cachePutRequests);
		}

		Object cacheValue;
		Object returnValue;

		if (cacheHit != null && !hasCachePut(contexts)) {
			// If there are no put requests, just use the cache hit 缓存命中切没有 @CachePut
			cacheValue = cacheHit.get();
			returnValue = wrapCacheValue(method, cacheValue);
		}
		else {
			// Invoke the method if we don't have a cache hit 调用被注解标识的方法
			returnValue = invokeOperation(invoker);
			cacheValue = unwrapReturnValue(returnValue);
		}

		// Collect any explicit @CachePuts
		collectPutRequests(contexts.get(CachePutOperation.class), cacheValue, cachePutRequests);

		// Process any collected put requests, either from @CachePut or a @Cacheable miss
  	// 往缓存中插入数据 
		for (CachePutRequest cachePutRequest : cachePutRequests) {
			cachePutRequest.apply(cacheValue);
		}

		// Process any late evictions  抑或是后删除缓存
		processCacheEvicts(contexts.get(CacheEvictOperation.class), false, cacheValue);

		return returnValue;
	}
```

### WebSocket 

Websocket 是全双工通信协议, STOMP(simple text oriented messaging protocol) 是简单文本协议, 让传输内容更加简单,socketJS是为了解决浏览器不支持websocket协议做的模拟websocket来工作