@LoadBalanced注解原理
2024-10-09 16:17:30
在使用springcloud ribbon客户端负载均衡的时候，可以给RestTemplate bean 加一个@LoadBalanced注解，就能让这个RestTemplate在请求时拥有客户端负载均衡的能力：
@Bean
@LoadBalanced
RestTemplate restTemplate() {
return new RestTemplate();
}
- 1
- 2
- 3
- 4
- 5
是不是很神奇?打开@LoadBalanced的注解源码，并没有什么特殊的东东
package org.springframework.cloud.client.loadbalancer;
import org.springframework.beans.factory.annotation.Qualifier;
import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Inherited;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
/**
- Annotation to mark a RestTemplate bean to be configured to use a LoadBalancerClient
- @author Spencer Gibb
*/
@Target({ ElementType.FIELD, ElementType.PARAMETER, ElementType.METHOD })
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@Qualifier
public @interface LoadBalanced {
}
- 1
- 2
- 3
- 4
- 5
- 6
- 7
- 8
- 9
- 10
- 11
- 12
- 13
- 14
- 15
- 16
- 17
- 18
- 19
- 20
- 21
- 22
唯一不同的地方就是多了一个@Qulifier注解.
搜索@LoadBalanced注解的使用地方，发现只有一处使用了,在LoadBalancerAutoConfiguration这个自动装配类中：
@LoadBalanced
@Autowired(required = false)
private List<RestTemplate> restTemplates = Collections.emptyList();
@Bean
public SmartInitializingSingleton loadBalancedRestTemplateInitializer(
final List<RestTemplateCustomizer> customizers) {
return new SmartInitializingSingleton() {
@Override
public void afterSingletonsInstantiated() {
for (RestTemplate restTemplate : LoadBalancerAutoConfiguration.this.restTemplates) {
for (RestTemplateCustomizer customizer : customizers) {
customizer.customize(restTemplate);
}
}
}
};
}
@Autowired(required = false)
private List<LoadBalancerRequestTransformer> transformers = Collections.emptyList();
@Bean
@ConditionalOnMissingBean
public LoadBalancerRequestFactory loadBalancerRequestFactory(
LoadBalancerClient loadBalancerClient) {
return new LoadBalancerRequestFactory(loadBalancerClient, transformers);
}
@Configuration
@ConditionalOnMissingClass("org.springframework.retry.support.RetryTemplate")
static class LoadBalancerInterceptorConfig {
@Bean
public LoadBalancerInterceptor ribbonInterceptor(
LoadBalancerClient loadBalancerClient,
LoadBalancerRequestFactory requestFactory) {
return new LoadBalancerInterceptor(loadBalancerClient, requestFactory);
}
@Bean
@ConditionalOnMissingBean
public RestTemplateCustomizer restTemplateCustomizer(
final LoadBalancerInterceptor loadBalancerInterceptor) {
return new RestTemplateCustomizer() {
@Override
public void customize(RestTemplate restTemplate) {
List<ClientHttpRequestInterceptor> list = new ArrayList<>(
restTemplate.getInterceptors());
list.add(loadBalancerInterceptor);
restTemplate.setInterceptors(list);
}
};
}
}
- 1
- 2
- 3
- 4
- 5
- 6
- 7
- 8
- 9
- 10
- 11
- 12
- 13
- 14
- 15
- 16
- 17
- 18
- 19
- 20
- 21
- 22
- 23
- 24
- 25
- 26
- 27
- 28
- 29
- 30
- 31
- 32
- 33
- 34
- 35
- 36
- 37
- 38
- 39
- 40
- 41
- 42
- 43
- 44
- 45
- 46
- 47
- 48
- 49
- 50
- 51
- 52
- 53
- 54
- 55
这段自动装配的代码的含义不难理解，就是利用了RestTempllate的拦截器，使用RestTemplateCustomizer对所有标注了@LoadBalanced的RestTemplate Bean添加了一个LoadBalancerInterceptor拦截器，而这个拦截器的作用就是对请求的URI进行转换获取到具体应该请求哪个服务实例ServiceInstance。
那么为什么
@LoadBalanced
@Autowired(required = false)
private List<RestTemplate> restTemplates = Collections.emptyList();
- 1
- 2
- 3
这个restTemplates能够将所有标注了@LoadBalanced的RestTemplate自动注入进来呢？这就要说说@Autowired注解和@Qualifier这两个注解了。
大家日常使用很多都是用@Autowired来注入一个bean,其实@Autowired还可以注入List和Map,比如我定义两个Bean:
@RestController
public class MyController {
<span class="token annotation punctuation">@Autowired</span><span class="token punctuation">(</span>required <span class="token operator">=</span> <span class="token boolean">false</span><span class="token punctuation">)</span>
<span class="token keyword">private</span> <span class="token class-name">List</span><span class="token generics"><span class="token punctuation"><</span><span class="token class-name">User</span><span class="token punctuation">></span></span> users <span class="token operator">=</span> <span class="token class-name">Collections</span><span class="token punctuation">.</span><span class="token function">emptyList</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token annotation punctuation">@Autowired</span><span class="token punctuation">(</span>required <span class="token operator">=</span> <span class="token boolean">false</span><span class="token punctuation">)</span>
<span class="token keyword">private</span> <span class="token class-name">Map</span><span class="token generics"><span class="token punctuation"><</span><span class="token class-name">String</span><span class="token punctuation">,</span><span class="token class-name">User</span><span class="token punctuation">></span></span> userMap <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">HashMap</span><span class="token generics"><span class="token punctuation"><</span><span class="token punctuation">></span></span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token annotation punctuation">@RequestMapping</span><span class="token punctuation">(</span><span class="token string">"/list"</span><span class="token punctuation">)</span>
<span class="token keyword">public</span> <span class="token class-name">Object</span> <span class="token function">listUsers</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{<!-- --></span>
<span class="token keyword">return</span> users<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token annotation punctuation">@RequestMapping</span><span class="token punctuation">(</span><span class="token string">"/map"</span><span class="token punctuation">)</span>
<span class="token keyword">public</span> <span class="token class-name">Object</span> <span class="token function">mapUsers</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{<!-- --></span>
<span class="token keyword">return</span> userMap<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
}
- 1
- 2
- 3
- 4
- 5
- 6
- 7
- 8
- 9
- 10
- 11
- 12
- 13
- 14
- 15
- 16
- 17
- 18
在controller中通过:
@Autowired(required = false)
private List<User> users = Collections.emptyList();
@Autowired(required = false)
private Map<String,User> userMap = new HashMap<>();
- 1
- 2
- 3
- 4
- 5
就可以自动将两个bean注入进来，当注入map的时候，map的key必须是String类型，然后bean name将作为map的key,本例，map中将有两个key分别为user1和user2,value分别为对应的User Bean实例。
访问http://localhost:8080/map:
{
"user1": {
"id": "1",
"name": "a"
},
"user2": {
"id": "2",
"name": "b"
}
}
- 1
- 2
- 3
- 4
- 5
- 6
- 7
- 8
- 9
- 10
- 11
访问http://localhost:8080/list:
[
{
"id": "1",
"name": "a"
},
{
"id": "2",
"name": "b"
}
]
- 1
- 2
- 3
- 4
- 5
- 6
- 7
- 8
- 9
- 10
然后我们给user1和user2分别打上@Qualifier修饰符:
@Bean("user1")
@Qualifier("valid")
User user1() {
return new User("1", "a");
}
@Bean("user2")
@Qualifier("invalid")
User user2() {
return new User("2", "b");
}
- 1
- 2
- 3
- 4
- 5
- 6
- 7
- 8
- 9
- 10
- 11
然后将controller中的user list 和user map分别也打上@Qualifier修饰符:
@RestController
public class MyController {
<span class="token annotation punctuation">@Autowired</span><span class="token punctuation">(</span>required <span class="token operator">=</span> <span class="token boolean">false</span><span class="token punctuation">)</span>
<span class="token annotation punctuation">@Qualifier</span><span class="token punctuation">(</span><span class="token string">"valid"</span><span class="token punctuation">)</span>
<span class="token keyword">private</span> <span class="token class-name">List</span><span class="token generics"><span class="token punctuation"><</span><span class="token class-name">User</span><span class="token punctuation">></span></span> users <span class="token operator">=</span> <span class="token class-name">Collections</span><span class="token punctuation">.</span><span class="token function">emptyList</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token annotation punctuation">@Autowired</span><span class="token punctuation">(</span>required <span class="token operator">=</span> <span class="token boolean">false</span><span class="token punctuation">)</span>
<span class="token annotation punctuation">@Qualifier</span><span class="token punctuation">(</span><span class="token string">"invalid"</span><span class="token punctuation">)</span>
<span class="token keyword">private</span> <span class="token class-name">Map</span><span class="token generics"><span class="token punctuation"><</span><span class="token class-name">String</span><span class="token punctuation">,</span><span class="token class-name">User</span><span class="token punctuation">></span></span> userMap <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">HashMap</span><span class="token generics"><span class="token punctuation"><</span><span class="token punctuation">></span></span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token annotation punctuation">@RequestMapping</span><span class="token punctuation">(</span><span class="token string">"/list"</span><span class="token punctuation">)</span>
<span class="token keyword">public</span> <span class="token class-name">Object</span> <span class="token function">listUsers</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{<!-- --></span>
<span class="token keyword">return</span> users<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token annotation punctuation">@RequestMapping</span><span class="token punctuation">(</span><span class="token string">"/map"</span><span class="token punctuation">)</span>
<span class="token keyword">public</span> <span class="token class-name">Object</span> <span class="token function">mapUsers</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{<!-- --></span>
<span class="token keyword">return</span> userMap<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
}
- 1
- 2
- 3
- 4
- 5
- 6
- 7
- 8
- 9
- 10
- 11
- 12
- 13
- 14
- 15
- 16
- 17
- 18
- 19
- 20
- 21
那么所有标注了@Qualifier(“valid”)的user bean都会自动注入到List users中去(本例是user1)，所有标注了@Qualifier(“invalid”)的user bean都会自动注入到Map<String,User> userMap中去（本例是user2），我们再次访问上面两个url:
访问http://localhost:8080/list:
[
{
"id": "1",
"name": "a"
}
]
- 1
- 2
- 3
- 4
- 5
- 6
- 7
访问http://localhost:8080/map:
{
"user2": {
"id": "2",
"name": "b"
}
}
- 1
- 2
- 3
- 4
- 5
- 6
- 7
看到这里我们可以理解@LoadBalanced的用处了，其实就是一个修饰符，和@Qualifier一样，比如我们给user1打上@LoadBalanced:
@Bean("user1")
@LoadBalanced
User user1() {
return new User("1", "a");
}
@Bean("user2")
User user2() {
return new User("2", "b");
}
- 1
- 2
- 3
- 4
- 5
- 6
- 7
- 8
- 9
- 10
然后controller中给List users打上@LoadBalanced注解:
@Autowired(required = false)
@LoadBalanced
private List<User> users = Collections.emptyList();
- 1
- 2
- 3
访问http://localhost:8080/list：
[
{
"id": "1",
"name": "a"
}
]
- 1
- 2
- 3
- 4
- 5
- 6
- 7
和@Qualifier注解效果一样，只有user1被注入进了List，user2没有修饰符，没有被注入进去。
另外当spring容器中有多个相同类型的bean的时候，可以通过@Qualifier来进行区分，以便在注入的时候明确表明你要注入具体的哪个bean,消除歧义。
最新文章
- [No0000A7]批处理经常用到的变量及批处理>NUL详细介绍
- .NET/ASP.NET MVC（模块化开发AraeRegistration）
- Hibernate一对一、一对多、多对多注解映射配置
- springboot+druid
- android 瀑布流效果 保存地址
- Install Sogoupinyin in Ubuntu
- zabbix 3.0快速安装简介（centos 7）
- [计算机图形学] 基于C#窗口的Bresenham直线扫描算法、种子填充法、扫描线填充法模拟软件设计（二）
- laravel elixir
- android怎么换背景图片
- spring和redis的整合-超越昨天的自己系列（7）
- span里设置高度
- 各种编码之间的关系以及getBytes的使用
- php ajax 下拉加载数据
- TagHelper+Layui封装组件之Radio单选框
- SQLServer之修改用户自定义数据库用户
- 基于GPS数据建立隐式马尔可夫模型预测目的地
- Codeforces 1136E Nastya Hasn't Written a Legend 线段树
- ： LDAP & Implementation
- 【转】C/C++内存泄漏及检测