SpringBoot的HttpMessageConverter使用（1）RestTemplate中的应用

场景：某次上线后，导致别的接口RestTemplate调用出现了异常。

1. 起因

经过排查后发现，某次上线的需求增加了该依赖：

    com.fasterxml.jackson.dataformat
    jackson-dataformat-xml
    2.11.0
    compile

被影响的接口：

@Slf4j
@RestController
public class OrderController {

    @Autowired
    private RestTemplate restTemplate;

    //测试http调用
    @RequestMapping(value = "/test3")
    public OrderDto get3() {
        String url = "http://localhost:8011/consumer/dept/get";
        OrderDto orderDto = new OrderDto();
        orderDto.setId(100110L);
        orderDto.setName("tom is mao");
        ResponseEntity results = restTemplate.postForEntity(url, orderDto, String.class);
        log.info("打印响应报文{}...", results);
        return orderDto;
    }
}

全局RestTemplate配置：

@Configuration
@Slf4j
public class RestTemplateConfiguration {

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

    @Bean
    public HttpComponentsClientHttpRequestFactory clientHttpRequestFactory() {
        try {
            HttpClientBuilder httpClientBuilder = HttpClientBuilder.create();
            RegistryBuilder socketFactoryRegistry = RegistryBuilder.create().
                    register("http", PlainConnectionSocketFactory.getSocketFactory());// 注册http和https请求
            // 开始设置连接池
            PoolingHttpClientConnectionManager poolingHttpClientConnectionManager = new PoolingHttpClientConnectionManager(socketFactoryRegistry.build());
            poolingHttpClientConnectionManager.setMaxTotal(500); // 最大连接数500
            poolingHttpClientConnectionManager.setDefaultMaxPerRoute(100); // 同路由并发数100
            httpClientBuilder.setConnectionManager(poolingHttpClientConnectionManager);
            httpClientBuilder.setRetryHandler(new DefaultHttpRequestRetryHandler(3, true)); // 重试次数
            HttpClient httpClient = httpClientBuilder.build();
            HttpComponentsClientHttpRequestFactory clientHttpRequestFactory = new HttpComponentsClientHttpRequestFactory(httpClient); // httpClient连接配置
            clientHttpRequestFactory.setConnectTimeout(20000);              // 连接超时
            clientHttpRequestFactory.setReadTimeout(30000);                 // 数据读取超时时间
            clientHttpRequestFactory.setConnectionRequestTimeout(20000);    // 连接不够用的等待时间
            return clientHttpRequestFactory;
        } catch (Exception e) {
            log.error("初始化HTTP连接池出错", e);
        }
        return null;
    }
}

经过排查后发现：发送的请求报文被序列化成了xml格式，但该接口之前为JSON格式。

2. 解决方案

2.1 方案一

1. 显式的声明Content-Type的类型：

@Slf4j
@RestController
public class OrderController {

    @Autowired
    private RestTemplate restTemplate;

    //测试http调用
    @RequestMapping(value = "/test5")
    public OrderDto get5() {
        String url = "http://localhost:8011/consumer/dept/get";
        
        OrderDto orderDto = new OrderDto();
        orderDto.setId(100110L);
        orderDto.setName("tom is mao");

        HttpHeaders headers = new HttpHeaders();
        headers.setContentType(MediaType.APPLICATION_JSON);
        HttpEntity httpEntity = new HttpEntity<>(orderDto,headers);
        
        ResponseEntity results = restTemplate.postForEntity(url, httpEntity, String.class);
        log.info("打印响应报文{}...", results);
        return orderDto;
    }
}

2.2 方案二

本次被影响的接口由于没有显式的声明请求的Content-type类型（即使用RestTemplate默认的消息转换器）。而由于引入了jackson-dataformat-xml依赖，导致消息转换器由JSON格式转换为XML格式。

2.2.1 消息转换器参与序列化

源码分析：org.springframework.web.client.RestTemplate.HttpEntityRequestCallback#doWithRequest

@Override
@SuppressWarnings("unchecked")
public void doWithRequest(ClientHttpRequest httpRequest) throws IOException {
   super.doWithRequest(httpRequest);
   Object requestBody = this.requestEntity.getBody();
   if (requestBody == null) {
      HttpHeaders httpHeaders = httpRequest.getHeaders();
      HttpHeaders requestHeaders = this.requestEntity.getHeaders();
      if (!requestHeaders.isEmpty()) {
         requestHeaders.forEach((key, values) -> httpHeaders.put(key, new LinkedList<>(values)));
      }
      if (httpHeaders.getContentLength() < 0) {
         httpHeaders.setContentLength(0L);
      }
   }
   else {
      Class requestBodyClass = requestBody.getClass();
      Type requestBodyType = (this.requestEntity instanceof RequestEntity ?
            ((RequestEntity)this.requestEntity).getType() : requestBodyClass);
      HttpHeaders httpHeaders = httpRequest.getHeaders();
      HttpHeaders requestHeaders = this.requestEntity.getHeaders();
      MediaType requestContentType = requestHeaders.getContentType();
      //若requestBody不为空，遍历消息转换器，获取到适合的消息转换
      for (HttpMessageConverter messageConverter : getMessageConverters()) {
         if (messageConverter instanceof GenericHttpMessageConverter) {
            GenericHttpMessageConverter