使用Spring RestTemplate 详解实践使用及拓展增强

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这篇文章主要介绍了使用Spring RestTemplate 详解实践使用及拓展增强，具有很好的参考价值，希望对大家有所帮助。如有错误或未考虑完全的地方，望不吝赐教
目录

RestTemplate 是什么？
主要类和接口
基础使用
- Get获取对象或对象集合
- Post 发送对象或集合
- 上传文件
- 上传多个文件
Spring RestTemplate 拓展
- 继承RestTemplate 拓展get方法
- 拓展URI处理逻辑
- 实际使用
- 思考进一步封装

RestTemplate 是什么？
RestTemplate 是Spring封装的一个Rest风格http请求框架，底层可以切换成HttpClient OkHttp 或者Netty实现，用户只需要关心RestTemplate怎么用而不需要关心底层框架如何操作，使用RestTemplate不需要关心如何手动转换返回的对象和到处都是的异常处理代码，可以让你的代码更简洁更优雅。

你可以在 spring-web 中找到它

主要类和接口

RestOperations 定义Rest 操作的接口
HttpAccessor 抽象http help 类
InterceptingHttpAccessor HttpAccess 装饰类拓展了拦截器功能
RestTemplate 具体实现类
ClientHttpRequestInterceptor 拦截器接口用于拦截http请求
UriTemplateHandler uri模板处理器，后面拓展会用到

基础使用
put delete 等方法参考get post 的写法

Get获取对象或对象集合
获取 Employee 集合

RestTemplate restTemplate = new RestTemplate();
ResponseEntity<List<Employee>> response = restTemplate.exchange(
  "http://localhost:8080/employees/",
  HttpMethod.GET,
  null,
  new ParameterizedTypeReference<List<Employee>>(){});
List<Employee> employees = response.getBody();

返回对象list用exchange方法使用 ParameterizedTypeReference 指定返回类型，getForEntity 也可以使用 Object[].class 或其他数组接收再转为List
获取单个对象

public class EmployeeList {
  private List<Employee> employees;
 
  public EmployeeList() {
    employees = new ArrayList<>();
  }
 
  // getter/setter
}
EmployeeList response = restTemplate.getForObject(
  "http://localhost:8080/employees",
  EmployeeList.class);
List<Employee> employees = response.getEmployees();

Post 发送对象或集合
发送集合

List<Employee> newEmployees = new ArrayList<>();
newEmployees.add(new Employee(3, "Intern"));
newEmployees.add(new Employee(4, "CEO"));
 
restTemplate.postForObject(
  "http://localhost:8080/employees/",
  newEmployees,
  ResponseEntity.class);

发送对象

List<Employee> newEmployees = new ArrayList<>();
newEmployees.add(new Employee(3, "Intern"));
newEmployees.add(new Employee(4, "CEO"));
 
restTemplate.postForObject(
  "http://localhost:8080/employees",
  new EmployeeList(newEmployees),
  ResponseEntity.class);

上传文件

public void uploadFile(){
  HttpHeaders headers = new HttpHeaders();
  //设置Content-Type
  headers.setContentType(MediaType.MULTIPART_FORM_DATA);
  MultiValueMap<String, Object> body
    = new LinkedMultiValueMap<>();
  body.add("file", getTestFile());
  HttpEntity<MultiValueMap<String, Object>> requestEntity
   = new HttpEntity<>(body, headers);
   
  String serverUrl = "http://localhost:8082/spring-rest/fileserver/singlefileupload/";
   
  RestTemplate restTemplate = new RestTemplate();
  ResponseEntity<String> response = restTemplate
    .postForEntity(serverUrl, requestEntity, String.class);
}
public FileSystemResource getTestFile(){
  return new FileSystemResource("./test.md")
}

FileSystemResource 是spring中的一个类参考

上传多个文件
在上传单个文件的基础上多加几个文件

MultiValueMap<String, Object> body
  = new LinkedMultiValueMap<>();
body.add("files", getTestFile());
body.add("files", getTestFile());
body.add("files", getTestFile());
   
HttpEntity<MultiValueMap<String, Object>> requestEntity
  = new HttpEntity<>(body, headers);
 
String serverUrl = "http://localhost:8082/spring-rest/fileserver/multiplefileupload/";
 
RestTemplate restTemplate = new RestTemplate();
ResponseEntity<String> response = restTemplate
  .postForEntity(serverUrl, requestEntity, String.class);

Spring RestTemplate 拓展

解决restTemplate get* url参数必须写死的问题
解决get*方法不好添加header信息的问题

继承RestTemplate 拓展get方法

/**
* 继承RestTemplate 新加get* 方法 比原有的方法多了个 httpHeaders 参数
*/
public class CustomerRestTemplate extends RestTemplate {
  public <T> ResponseEntity<T> getForEntity(String url, HttpHeaders httpHeaders, Class<T> responseType, Object... uriVariables) throws RestClientException {
    HttpEntity<Object> requestEntity = new HttpEntity<>(httpHeaders);
    RequestCallback requestCallback = httpEntityCallback(requestEntity, responseType);
    ResponseExtractor<ResponseEntity<T>> responseExtractor = responseEntityExtractor(responseType);
    return execute(url, HttpMethod.GET, requestCallback, responseExtractor, uriVariables);
  }
  public <T> ResponseEntity<T> getForEntity(String url, HttpHeaders httpHeaders, Class<T> responseType, Map<String, ?> uriVariables) throws RestClientException {
    HttpEntity<Object> requestEntity = new HttpEntity<>(httpHeaders);
    RequestCallback requestCallback = httpEntityCallback(requestEntity, responseType);
    ResponseExtractor<ResponseEntity<T>> responseExtractor = responseEntityExtractor(responseType);
    return execute(url, HttpMethod.GET, requestCallback, responseExtractor, uriVariables);
  }
  public <T> T getForObject(String url, HttpHeaders httpHeaders, Class<T> responseType, Map<String, ?> uriVariables) throws RestClientException {
    HttpEntity<Object> requestEntity = new HttpEntity<>(httpHeaders);
    RequestCallback requestCallback = httpEntityCallback(requestEntity, responseType);
    ResponseExtractor<T> responseExtractor = new HttpMessageConverterExtractor<T>(responseType, getMessageConverters());
    return execute(url, HttpMethod.GET, requestCallback, responseExtractor, uriVariables);
  }
  public <T> T getForObject(String url, HttpHeaders httpHeaders, Class<T> responseType, Object... uriVariables) throws RestClientException {
    HttpEntity<Object> requestEntity = new HttpEntity<>(httpHeaders);
    RequestCallback requestCallback = httpEntityCallback(requestEntity, responseType);
    ResponseExtractor<T> responseExtractor = new HttpMessageConverterExtractor<T>(responseType, getMessageConverters());
    return execute(url, HttpMethod.GET, requestCallback, responseExtractor, uriVariables);
  }
}

拓展URI处理逻辑

/**
* 根据uriTemplate 把 uriVariables 分成两类 
* 一类是path params 一类是 query params 分开赋值
* 如 /xx/{id}/type  path params 就是 id uriVariables 剩下的就是query params 用？拼接在url后面
* 如果查询参数中有数组或集合类型的参数会转化成 key[]=value1&key[]=value2...
*/
public class QueryParamsUrlTemplateHandler extends DefaultUriTemplateHandler {
  /**
   * 匹配path param
   */
  private static final Pattern NAMES_PATTERN = Pattern.compile("\\{([^/]+?)\\}");
  @Override
  public URI expand(String uriTemplate, Map<String, ?> uriVariables) {
    UriComponentsBuilder uriComponentsBuilder = UriComponentsBuilder.fromHttpUrl(uriTemplate);
    //解析uriTemplate 提取query param
    Map<String, ?> queryParam = getQueryParam(uriTemplate, uriVariables);
    //设置query param
    queryParam.forEach((k, v) -> {
      if (v instanceof Object[]) {
        Object[] arrayParam = (Object[]) v;
        //把数组类型的参数拼成 参数名 + [] 的形式 k[]  xx&kp[]=xx&k[]=xx
        String key = k + "[]";
        String strArrayParam = Stream.of(arrayParam).map(String::valueOf).collect(Collectors.joining("&" + key + "="));
        uriComponentsBuilder.queryParam(key, strArrayParam);
      } else if (v instanceof Iterable) {
        Iterable iterable = (Iterable) v;
        String key = k + "[]";
        String strArrayParam = Stream.of(iterable).map(String::valueOf).collect(Collectors.joining("&" + key + "="));
        uriComponentsBuilder.queryParam(key, strArrayParam);
      } else {
        uriComponentsBuilder.queryParam(k, v);
      }
    });
    uriTemplate = uriComponentsBuilder.build().toUriString();
    //设置path param
    return super.expand(uriTemplate, uriVariables);
  }
  /**
   * 解析uriTemplate 分离 query param
   *
   * @param uriTemplate  uri模板
   * @param uriVariables 全部的模板变量
   * @return 查询变量
   */
  public Map<String, ?> getQueryParam(String uriTemplate, Map<String, ?> uriVariables) {
    if (uriTemplate == null) {
      return null;
    }
    if (uriTemplate.indexOf('{') == -1) {
      return uriVariables;
    }
    if (uriTemplate.indexOf(':') != -1) {
      uriTemplate = sanitizeSource(uriTemplate);
    }
    Map<String, Object> pathVariables = Maps.newHashMap();
    Matcher matcher = NAMES_PATTERN.matcher(uriTemplate);
    while (matcher.find()) {
      String matchKey = matcher.group(1);
      Object value = uriVariables.get(matchKey);
      if (value != null) {
        pathVariables.put(matchKey, value);
      }
    }
    //此处为了图方便使用了 guava 工具包中的类 功能就是取差集
    MapDifference<String, Object> difference = Maps.difference(uriVariables, pathVariables);
    return difference.entriesOnlyOnLeft();
  }
  /**
   * Remove nested "{}" such as in URI vars with regular expressions.
   */
  private static String sanitizeSource(String source) {
    int level = 0;
    StringBuilder sb = new StringBuilder();
    for (char c : source.toCharArray()) {
      if (c == '{') {
        level++;
      }
      if (c == '}') {
        level--;
      }
      if (level > 1 || (level == 1 && c == '}')) {
        continue;
      }
      sb.append(c);
    }
    return sb.toString();
  }
}

实际使用
初始化RestTemplate

SimpleClientHttpRequestFactory requestFactory = new SimpleClientHttpRequestFactory();
requestFactory.setConnectTimeout(500);// 设置超时
requestFactory.setReadTimeout(500);
//new 自己定义的类
CustomerRestTemplate restTemplate = new CustomerRestTemplate();
//设置自定义的uri处理处理器
QueryParamsUrlTemplateHandler queryParamsUrlTemplateHandler = new QueryParamsUrlTemplateHandler();
//这里使用装饰模式 添加rootUri
RootUriTemplateHandler rootUriTemplateHandler = new RootUriTemplateHandler(outUrl, queryParamsUrlTemplateHandler);
restTemplate.setUriTemplateHandler(rootUriTemplateHandler);
restTemplate.setRequestFactory(requestFactory);

get请求示例

Map<String, Object> params = new HashMap<>();
params.put("id", "1");
params.put("param2", "2");
params.put("param", new Integer[]{1506, 1507});
HttpHeaders httpHeaders = new HttpHeaders();
httpHeaders.add("Authorization", "Basic " + "your authorization");
ResponseEntity<Map[]> forEntity = restTemplate.getForEntity("/api/test/{id}", httpHeaders, Map[].class, params);
// url 为 api/test/1?param[]=1506&param[]=1507&param2=2

思考进一步封装
可以考虑使用建造者模式改造restTemplate

Employee employee = RestTemplate.build()
      .get("api/xxx/{id}")
      .header("xx","xx")
      .headers(new Headers())
      .param("xx","xx")
      .params(new HashMap(){{put("bb","bb");}})
      .targetClass(Employee.class)
      .execute();

以上为个人经验，希望能给大家一个参考，也希望大家多多支持CodeAE代码之家。
原文链接：https://blog.csdn.net/isyoungboy/article/details/86608877

[Java] 使用Spring RestTemplate 详解实践使用及拓展增强

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