RestTemplate 连接池配置

通过 RestTemplateBuilder 的方式生成 RestTemplate

    @Bean(name = "template")
    RestTemplate template(RestTemplateBuilder restTemplateBuilder) {
        return restTemplateBuilder
                //单位s, 设置连接时间，避免线程过多被阻塞挂起
                .setConnectTimeout(Duration.ofSeconds(1))
                .setReadTimeout(Duration.ofSeconds(1))
                .additionalMessageConverters(new MyMappingJackson2HttpMessageConverter())
                .requestFactory(() -> {
                    HttpComponentsClientHttpRequestFactory clientHttpRequestFactory = new HttpComponentsClientHttpRequestFactory();
                    // 连接池
                    HttpClientBuilder httpClientBuilder = HttpClientBuilder.create();
                    //设置HTTP连接管理器
                    PoolingHttpClientConnectionManager poolingConnectionManager = new PoolingHttpClientConnectionManager();
                    poolingConnectionManager.setMaxTotal(500); // 连接池最大连接数
                    poolingConnectionManager.setDefaultMaxPerRoute(200); // 每个主机的并发
                    httpClientBuilder.setConnectionManager(poolingConnectionManager);
                    // 设置连接池
                    clientHttpRequestFactory.setHttpClient(httpClientBuilder.build());
                    return clientHttpRequestFactory;
                })
                .build();
    }

restTemplate的连接由 RequestFactory 创建
HttpComponentsClientHttpRequestFactory 是 RequestFactory 实现类，连接池化，有 httpClient 引用

RestTemplateBuilder 用于生成 restTeamplte
configure 方法初始化了 RequestFactory 对象通过 buildRequestFactory

    public ClientHttpRequestFactory buildRequestFactory() {
        ClientHttpRequestFactory requestFactory = null;
        if (this.requestFactory != null) {
            requestFactory = (ClientHttpRequestFactory)this.requestFactory.get();
        } else if (this.detectRequestFactory) {
            // 默认连接池工厂
            requestFactory = (new ClientHttpRequestFactorySupplier()).get();
        }

        if (requestFactory != null && this.requestFactoryCustomizer != null) {
            this.requestFactoryCustomizer.accept(requestFactory);
        }

        return requestFactory;
    }