一、理论基础

RestTemplate是Springboot中内置的Http请求工具，可以直接注入使用。

两个常用的构造方法如下图 (点击进入文档地址)

image.png

从上面可以看出，最简单的方式就是使用默认配置，不需要额外的配置，便可以直接使用该工具。对于请求频次比较低的情况下，默认配置完全够用。

如果需要大量的请求，可以自定义配置，使用HttpClient的连接池。

二、实战代码

2.1 依赖引入

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
    <exclusions>
        <exclusion>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-tomcat</artifactId>
        </exclusion>
    </exclusions>
</dependency>
<!-- 将tomcat替换为undertow -->
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-undertow</artifactId>
</dependency>

<!-- 自定义的元数据依赖 -->
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-configuration-processor</artifactId>
    <optional>true</optional>
</dependency>

<!-- httpclient，为了使用其连接池 -->
<dependency>
    <groupId>org.apache.httpcomponents</groupId>
    <artifactId>httpclient</artifactId>
    <version>4.5.12</version>
</dependency>

<!-- for fastjson -->
<dependency>
    <groupId>com.alibaba</groupId>
    <artifactId>fastjson</artifactId>
    <version>1.2.62</version>
</dependency>

<!-- lombok，减少代码量，idea需要安装lombok插件 -->
<dependency>
    <groupId>org.projectlombok</groupId>
    <artifactId>lombok</artifactId>
    <optional>true</optional>
</dependency>

2.2 配置项

2.2.1 配置

http:
  pool:
    # 连接超时
    connectTimeout: 5000
    connectionRequestTimeout: 5000
    defaultMaxPerRoute: 20
    # 最大连接数
    maxTotal: 100
    # 服务器返回数据(response)的时间
    socketTimeout: 5000
    validateAfterInactivity: 30000

2.2.2 读取配置文件

@Component
@ConfigurationProperties(prefix = "http.pool")
@Data
public class HttpClientProperties {


    /**
     * 最大连接数
     */
    private Integer maxTotal;
    /**
     * 路由是对最大连接数的细分
     * 每个路由基础的连接数
     */
    private Integer defaultMaxPerRoute;
    /**
     * 连接超时时间
     */
    private Integer connectTimeout;
    /**
     * 从连接池中获取连接的超时时间
     */
    private Integer connectionRequestTimeout;
    /**
     * 服务器返回数据(response)的时间
     */
    private Integer socketTimeout;
    /**
     * 可用空闲连接过期时间
     * 重用空闲连接时会先检查是否空闲时间超过这个时间，如果超过，释放socket重新建立
     */
    private Integer validateAfterInactivity;
}

2.3 配置文件

@Configuration
public class RestTemplateConfig {


    private final HttpClientProperties httpClientProperties;

    public RestTemplateConfig(HttpClientProperties httpClientProperties) {
        this.httpClientProperties = httpClientProperties;
    }


    @Bean
    public RestTemplate restTemplate(ClientHttpRequestFactory factory){
        return new RestTemplate(factory);
    }


    @Bean
    public ClientHttpRequestFactory clientHttpRequestFactory(){
        return new HttpComponentsClientHttpRequestFactory(httpClient());
    }


    @Bean
    public HttpClient httpClient() {
        Registry<ConnectionSocketFactory> registry = RegistryBuilder.<ConnectionSocketFactory>create()
                .register("http", PlainConnectionSocketFactory.getSocketFactory())
                .register("https", SSLConnectionSocketFactory.getSocketFactory())
                .build();
        PoolingHttpClientConnectionManager connectionManager = new PoolingHttpClientConnectionManager(registry);
        connectionManager.setMaxTotal(httpClientProperties.getMaxTotal());
        connectionManager.setDefaultMaxPerRoute(httpClientProperties.getDefaultMaxPerRoute());
        connectionManager.setValidateAfterInactivity(httpClientProperties.getValidateAfterInactivity());
        RequestConfig requestConfig = RequestConfig.custom()
                .setSocketTimeout(httpClientProperties.getSocketTimeout())
                .setConnectTimeout(httpClientProperties.getConnectTimeout())
                .setConnectionRequestTimeout(httpClientProperties.getConnectionRequestTimeout())
                .build();
        return HttpClientBuilder.create()
                .setDefaultRequestConfig(requestConfig)
                .setConnectionManager(connectionManager)
                .build();
    }
}

2.4 简单的工具类

@Component
@Slf4j
public class HttpClientUtils {

    private final RestTemplate restTemplate;

    public HttpClientUtils(RestTemplate restTemplate) {
        this.restTemplate = restTemplate;
    }

    /**
     * Get
     */
    public String get(String uri, Map<String, String> param, String token) {
        HttpHeaders headers = new HttpHeaders();
        headers.set("token", token);
        HttpEntity<String> requestEntity = new HttpEntity<>(null, headers);
        StringBuilder url = new StringBuilder();
        url.append(uri).append("?");
        param.forEach((k, v) -> url.append(k).append("=").append(v).append("&"));
        String getUrl = url.substring(0, url.length() - 1);
        ResponseEntity<CodeResult> response = restTemplate.exchange(getUrl, HttpMethod.GET, requestEntity, CodeResult.class);
        return parseCodeResult(response);
    }

    /**
     * post方式请求接口
     * - 参数形式：form-data
     */
    public String postFormData(String url, MultiValueMap<String, Object> paramMap, String token) {
        HttpHeaders headers = new HttpHeaders();
        headers.set("token", token);
        headers.setContentType(MediaType.MULTIPART_FORM_DATA);
        //用HttpEntity封装整个请求报文
        HttpEntity<MultiValueMap<String, Object>> files = new HttpEntity<>(paramMap, headers);
        ResponseEntity<CodeResult> response = restTemplate.postForEntity(url, files, CodeResult.class);
        return parseCodeResult(response);
    }

    /**
     * post方式请求接口
     * - 参数形式：json
     */
    public String postJson(String url, String param, String token) {
        HttpHeaders headers = new HttpHeaders();
        headers.setContentType(MediaType.APPLICATION_JSON);
        headers.set("token", token);
        HttpEntity<String> entity = new HttpEntity<>(param, headers);
        ResponseEntity<CodeResult> response = restTemplate.postForEntity(url, entity, CodeResult.class);
        return parseCodeResult(response);
    }

    /**
     * 解析云端服务接口返回值
     */
    public String parseCodeResult(ResponseEntity<CodeResult> response) {
        if (response.getStatusCodeValue() != HttpStatus.OK.value()) {
            throw new RuntimeException("网络请求失败,状态码:" + response.getStatusCodeValue());
        }
        CodeResult codeResult = response.getBody();
        assert codeResult != null;
        if (!codeResult.getSuccess()) {
            log.error("调用后台服务接口错误,返回值:{}", JSON.toJSON(codeResult));
            throw new RuntimeException("调用后台服务接口错误， 错误信息：" + codeResult.getMsg());
        }
        return JSON.toJSONString(codeResult.getData());
    }
}

三、源码地址

https://github.com/lysmile/spring-boot-demo/tree/master/spring-boot-resttemplate-demo