参考：

〇、介绍

spring-web框架下的一个http客户端，提供了一种通用的接口。

HTTP请求方式可以选择：

  • 原生的 java.net.HttpURLConnection
  • Apache HttpClient
  • …

HTTP请求方式通过 ClientHttpRequestFactory 接口适配，默认使用 SimpleClientHttpRequestFactory

AbstractClientHttpRequestFactoryWrapper, BufferingClientHttpRequestFactory, HttpComponentsAsyncClientHttpRequestFactory, HttpComponentsClientHttpRequestFactory, InterceptingClientHttpRequestFactory, MockMvcClientHttpRequestFactory, Netty4ClientHttpRequestFactory, OkHttp3ClientHttpRequestFactory, SimpleClientHttpRequestFactory

提供开箱即用的请求和响应序列化和反序列化工具，且支持高度定制化。接口为 HttpMessageConverter<>

一、构造方式

RestTemplate restTemplate = new RestTemplate();
  • HTTP请求方式使用 SimpleClientHttpRequestFactory 及 java.net.HttpURLConnection
  • 默认添加了众多消息处理器，参见：RestTemplate#RestTemplate()

当然spring还提供了其他的构造方式，例如：

SimpleClientHttpRequestFactory requestFactory = new SimpleClientHttpRequestFactory();
requestFactory.setConnectTimeout(1000);
requestFactory.setReadTimeout(1000);
RestTemplate restTemplate1 = new RestTemplate(requestFactory);

二、相关配置

1、requestFactory

HTTP请求方式配置

restTemplate.setRequestFactory(requestFactory);

支持介绍所描述的客户端，当然也可以自己实现 ClientHttpRequestFactory 接口

2、messageConverters

请求体与相应体的序列化、反序列化器

restTemplate.setMessageConverters(messageConverters);
  • messageConverters 类型为 List<HttpMessageConverter<?>>
  • 比如Json请求体的序列化和反序列化

支持如下方法：

AbstractGenericHttpMessageConverter, AbstractHttpMessageConverter, AbstractJackson2HttpMessageConverter, AbstractJaxb2HttpMessageConverter, AbstractJsonHttpMessageConverter, AbstractWireFeedHttpMessageConverter, AbstractXmlHttpMessageConverter, AllEncompassingFormHttpMessageConverter, AtomFeedHttpMessageConverter, BufferedImageHttpMessageConverter, ByteArrayHttpMessageConverter, FormHttpMessageConverter, GsonHttpMessageConverter, Jaxb2CollectionHttpMessageConverter, Jaxb2RootElementHttpMessageConverter, JsonbHttpMessageConverter, MappingJackson2CborHttpMessageConverter, MappingJackson2HttpMessageConverter, MappingJackson2SmileHttpMessageConverter, MappingJackson2XmlHttpMessageConverter, MarshallingHttpMessageConverter, ObjectToStringHttpMessageConverter, ProtobufHttpMessageConverter, ProtobufJsonFormatHttpMessageConverter, ResourceHttpMessageConverter, ResourceRegionHttpMessageConverter, RssChannelHttpMessageConverter, SourceHttpMessageConverter, StringHttpMessageConverter

3、interceptors

拦截器：配置请求之前的过滤请求

restTemplate.setInterceptors(interceptors);
  • interceptors 类型为 List<ClientHttpRequestInterceptor>
  • 用于实现请求之前的校验或者增强

4、errorHandler

异常处理器：用于处理请求响应码的异常。

restTemplate.setErrorHandler(errorHandler);
  • 只能处理http响应码的错误
  • 一定不要读取ClientHttpResponse.getBody，因为inputsteam只能读一次
  • 默认为 DefaultResponseErrorHandler
  • 面对国内http状态码为200的错误，只能在 messageConverter 层处理

三、相关API

常用API如下：

// get请求
getForObject
getForEntity
// post请求
postForXxx
// ...
  • ForObject表示 返回 T
  • ForEntity表示 返回 ResponseEntity<T>

通用API如下：

exchange
execute
  • 一般可以使用exchange进行封装，具有很高的灵活性

四、实例

1、处理url参数（get参数）

String url = "http://localhost:8080/test/sendSms?phone={phone}&msg={phone}";
String result = restOperations.getForObject(url, String.class, "151xxxxxxxx", "测试短信内容");

以下方式默认情况下不支持 （spring 5.x）

String url = "http://localhost:8080/test/sendSms?phone={phone}&msg={phone}";

Map<String, Object> uriVariables = new HashMap<String, Object>();
uriVariables.put("phone", "151xxxxxxxx");
uriVariables.put("msg", "测试短信内容");

String result = restOperations.getForObject(url, String.class, uriVariables);

2、配置请求头

例如配置cookie

HttpHeaders jsonHeaders = new HttpHeaders();// header参数
jsonHeaders.add(HttpHeaders.COOKIE, "sessionid=" + sessionid);
jsonHeaders.add(HttpHeaders.USER_AGENT, "test");
jsonHeaders.add(HttpHeaders.ACCEPT, "application/json");
jsonHeaders.add(HttpHeaders.CONTENT_TYPE, "application/json");
// request 为 requestbody （任意对象）
HttpEntity<?> requestEntity = new HttpEntity<>(request, jsonHeaders);
ResponseEntity<T> response = restTemplate.exchange(buildUrl(path), HttpMethod.POST, requestEntity, responseType,
    uriVariables);
return response.getBody();

3、form方式post请求

HttpHeaders formHeaders = new HttpHeaders();// header参数
formHeaders.add(HttpHeaders.COOKIE, "sessionid=" + sessionid);
formHeaders.add(HttpHeaders.USER_AGENT, "test");
formHeaders.add(HttpHeaders.ACCEPT, "application/json");
formHeaders.add(HttpHeaders.CONTENT_TYPE, "application/x-www-form-urlencoded");
// request 为Map<String, ?>
MultiValueMap<String, String> body = new LinkedMultiValueMap<>();
for (Map.Entry<String, ?> entry : request.entrySet()) {
    body.add(entry.getKey(), entry.getValue().toString());
}
HttpEntity<?> requestEntity = new HttpEntity<>(body, formHeaders);
ResponseEntity<T> response = restTemplate.exchange(buildUrl(path), HttpMethod.POST, requestEntity, responseType, uriVariables);
return response.getBody();

3、定制json解析器

注意使用了Jackson：

  • 定制日期序列化方式

  • 使用java8的日期时间标准

    restTemplate = new RestTemplate();
// 配置JSON解析器
ObjectMapper objectMapper = new ObjectMapper();
JavaTimeModule javaTimeModule = new JavaTimeModule();
// 设置时间格式
javaTimeModule.addDeserializer(LocalDateTime.class,
new LocalDateTimeDeserializer(DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss.SSS")));
objectMapper.registerModule(new ParameterNamesModule())
.registerModule(new Jdk8Module())
.registerModule(javaTimeModule);
// 忽略不存在字段
objectMapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
List<HttpMessageConverter<?>> messageConverters = restTemplate
.getMessageConverters()
.stream()
.filter(c -> !(c instanceof MappingJackson2HttpMessageConverter))
.collect(Collectors.toList());
MappingJackson2HttpMessageConverter jsonMessageConverter = new MappingJackson2HttpMessageConverter();
jsonMessageConverter.setObjectMapper(objectMapper);
messageConverters.add(new JsonHttpMessageConverterProxy(jsonMessageConverter));
restTemplate.setMessageConverters(messageConverters);

依赖如下

        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-databind</artifactId>
        </dependency>
        <dependency>
            <groupId>com.fasterxml.jackson.module</groupId>
            <artifactId>jackson-module-parameter-names</artifactId>
        </dependency>
        <dependency>
            <groupId>com.fasterxml.jackson.datatype</groupId>
            <artifactId>jackson-datatype-jdk8</artifactId>
        </dependency>
        <dependency>
            <groupId>com.fasterxml.jackson.datatype</groupId>
            <artifactId>jackson-datatype-jsr310</artifactId>
        </dependency>

4、定制200错误处理

例如如下情况：

正确返回

http-status-code 200

{
  "code": 0,
  "data": {},
  "message": "success"
}

错误返回

http-status-code 200

{
  "code": 1, // 非零
  "data": 11111, // 一个数字
  "message": "错误信息" // 错误信息
}

通过代理Jackson解析器实现

/**
 * 写这个代理的原因：报错 返回200。但是data的值不是null而是 一个 数字。
 * 不写这个代理会抛出序列化异常，从而无法获取错误信息
 */
class JsonHttpMessageConverterProxy implements HttpMessageConverter<Object> {

    private HttpMessageConverter<Object> converter;

    public JsonHttpMessageConverterProxy(HttpMessageConverter<Object> converter) {
        this.converter = converter;
    }

    @Override
    public boolean canRead(Class<?> clazz, MediaType mediaType) {
        return converter.canRead(clazz, mediaType);
    }

    @Override
    public boolean canWrite(Class<?> clazz, MediaType mediaType) {
        return converter.canWrite(clazz, mediaType);
    }

    @Override
    public List<MediaType> getSupportedMediaTypes() {
        return converter.getSupportedMediaTypes();
    }

    @Override
    public Object read(Class<? extends Object> clazz, HttpInputMessage inputMessage)
        throws IOException, HttpMessageNotReadableException {
        String body = new BufferedReader(new InputStreamReader(inputMessage.getBody()))
            .lines().collect(Collectors.joining(System.lineSeparator())).toString();
        Map<String, Object> bodyMap = JSON.parseObject(body);
        Integer code = (Integer) bodyMap.get("code");
        if (code != null && code != 0) {
            bodyMap.put("data", null);
            body = JSON.toJSONString(bodyMap);
        }
        InputStream fixBodyInputStream = new ByteArrayInputStream(body.getBytes());
        return converter.read(clazz, new HttpInputMessage() {

            @Override
            public HttpHeaders getHeaders() {
                return inputMessage.getHeaders();
            }

            @Override
            public InputStream getBody() throws IOException {
                return fixBodyInputStream;
            }
        });
    }

    @Override
    public void write(Object t, MediaType contentType, HttpOutputMessage outputMessage)
        throws IOException, HttpMessageNotWritableException {
        converter.write(t, contentType, outputMessage);
    }
}

使用发方式

restTemplate = new RestTemplate();
// 配置JSON解析器
ObjectMapper objectMapper = new ObjectMapper();
// 其他配置...
MappingJackson2HttpMessageConverter jsonMessageConverter = new MappingJackson2HttpMessageConverter();
jsonMessageConverter.setObjectMapper(objectMapper);
List<HttpMessageConverter<?>> messageConverters = restTemplate
                      .getMessageConverters()
                      .stream()
                      .filter(c -> !(c instanceof MappingJackson2HttpMessageConverter))
                      .collect(Collectors.toList());
// 使用这个代理
messageConverters.add(new JsonHttpMessageConverterProxy(jsonMessageConverter));
restTemplate.setMessageConverters(messageConverters);