Spring-使用REST服务

概述

对于RESTful API,返回的一般是json字符串,如果后台想调用别人的RESTful API则需要解析json

Spring提供了更简单的方式可以自动将数据封装为对象使用

1. 摘要

• 通过RestTemplate调用REST服务
• 通过Traverson导航RESTful API

通过RestTemplate调用REST服务

1.SSL证书

注意: 对于使用SSL,启用了HTTPS则需要验证证书

简单介绍: 使用jdk的keytool命令创建自定义SSL证书且在本地localhost测试需要的相关配置

1.1. 相关命令

    /*** 为了方便统一在jdk安装目录运行如: jdk-14.0.1\lib\security ***/
    //生成服务端私钥: 别名为tomcat,文件名为mykeys.jks
    keytool -keystore mykeys.jks -genkey -alias tomcat -keyalg RSA
    //根据私钥导出服务端证书保存为server.crt
    keytool -export -alias tomcat -keystore mykeys.jks -file server.crt
    //jdk: 导入别名为tomcat的证书到cacerts中
    keytool -import -v -trustcacerts -alias tomcat -file server.crt -storepass changeit -keystore cacerts
    //jdk: 从cacerts中删除证书别名为tomcat
    keytool -delete -alias tomcat -keystore cacerts -storepass changeit

1.2.步骤

• 创建

  keytool -keystore mykeys.jks -genkey -alias tomcat -keyalg RSA
  Enter keystore password:
  Re-enter new password:
  What is your first and last name?
    [Unknown]:  localhost
  What is the name of your organizational unit?
    [Unknown]:  localhost
  What is the name of your organization?
    [Unknown]:  localhost
  What is the name of your City or Locality?
    [Unknown]:  localhost
  What is the name of your State or Province?
    [Unknown]:  localhost
  What is the two-letter country code for this unit?
    [Unknown]:  in
  Is CN=localhost, OU=localhost, O=localhost, L=localhost, ST=localhost, C=in correct?
    [no]:  yes

• 导出

  keytool -export -alias tomcat -keystore mykeys.jks -file server.crt

• jdk导入

  keytool -import -v -trustcacerts -alias tomcat -file server.crt -storepass changeit -keystore cacerts

2. API

方法	描述
RestTemplate()	构造方法
delete(…)	发送DELETE请求,根据指定的URL
exchange(…)	根据指定的URL和请求方式发送请求,返回ResponseEntity(封装响应信息及响应体)
execute(…)	根据指定的URL和请求方式发送请求,将响应体封装到指定类型对象返回
getForEntity(…)	发送GET请求,返回一个ResponseEntity对象(封装了响应信息及响应体)
getForObject(…)	发送GET请求,将响应体封装到指定的类型对象中返回
headForHeaders(…)	发送HEAD请求,返回指定URL的响应头
optionsForAllow(…)	发送OPTIONS请求,返回指定URL的ALlow header
patchForObject(…)	发送PATCH请求,将响应体封装到指定对象中返回
postForEntity(…)	发送POST请求,返回一个ResponseEntity对象
postForLocation(…)	发送POST请求,创建资源并返回资源链接
postForObject(…)	发送POST请求,将响应体封装到指定类型对象中返回
put(…)	根据指定的URL发送PUT请求

3. GET

发送GET请求获取资源

    public PopInStock getPopInStockById(int id){
        RestTemplate restTemplate = new RestTemplate();
        PopInStock pop = null;
        String url = "https://localhost:8443/api/popInStocks/{id}";
        //方式一: 直接传入id
        //pop = restTemplate.getForObject(url, PopInStock.class, id);

        //方式二: 传入map
        HashMap<String,Integer> map = new HashMap<>(1);
        map.put("id",id);
        //pop = restTemplate.getForObject(url,PopInStock.class,map);

        //方式三: 通过URI参数
        URI uri = UriComponentsBuilder.fromHttpUrl(url).build(id);
        //pop = restTemplate.getForObject(uri,PopInStock.class);

        //方式四: 通过getForEntity方法,返回ResponseEntity对象(记录了详细的响应信息)
        ResponseEntity<PopInStock> responseEntity = restTemplate.getForEntity(url,PopInStock.class,id);
        pop = responseEntity.getBody();

        return pop;
    }

4.PUT

发送PUT请求更新资源

• *注意: * 如果开启了Spring Security的csrf防护,则需要关闭RESTful API请求的防护才行

  @Configuration
  @EnableWebSecurity
  public class SecurityConfiguration extends WebSecurityConfigurerAdapter {
      @Override
      protected void configure(HttpSecurity http) throws Exception {
           http.csrf().ignoringAntMatchers("api/**");
      }
  }

• 实例

      //更新
      public void updatePopInStock(PopInStock popInStock){
          RestTemplate restTemplate = new RestTemplate();
          String url = "https://localhost:8443/api/popInStocks/{id}";
          restTemplate.put(url,popInStock,popInStock.getId());
      }

5.DELETE

发送DELETE请求删除资源

    //删除
    public void deletePopInStock(int id){
        RestTemplate restTemplate = new RestTemplate();
        String url = "https://localhost:8443/api/popInStocks/{id}";
        restTemplate.delete(url,id);
    }

6.POST

发送POST请求新增资源

    //新增
    public PopInStock createPopInStock(PopInStock popInStock){
        RestTemplate restTemplate = new RestTemplate();
        String url = "https://localhost:8443/api/popInStocks";
        return restTemplate.postForObject(url,popInStock,PopInStock.class);
    }
    public URI createPopInStockLocation(PopInStock popInStock){
        RestTemplate restTemplate = new RestTemplate();
        String url = "https://localhost:8443/api/popInStocks";
        return restTemplate.postForLocation(url,popInStock);
    }
    public PopInStock createPopInStockEntity(PopInStock popInStock){
        RestTemplate restTemplate = new RestTemplate();
        String url = "https://localhost:8443/api/popInStocks";
        ResponseEntity<PopInStock> responseEntity = restTemplate.postForEntity(url,popInStock,PopInStock.class);
        return responseEntity.getBody();
    }

通过Traverson导航RESTful API

• Traverson 是 Spring Data HATEOAS提供的用于方便导航RESTful API,即根据返回的json通过其字段名即可导航到其值
• Traverson 只能导航到连接进行查询操作,对于POST PUT DELETE操作须使用RestTemplate

实例

    public void traverson(){
        //创建Traverson
        Traverson traverson = new Traverson(URI.create("https://localhost:8443/api"), MediaTypes.HAL_JSON);
        //获取PopInStocks
        ParameterizedTypeReference<CollectionModel<PopInStock>> popInStocksType = new ParameterizedTypeReference<>(){};
        /** 1 **/
        CollectionModel<PopInStock> popInStocks = traverson.follow("pops")//根据json字段名
                .toObject(popInStocksType);//因为泛型擦除的特性,无法传入正常的泛型类型,因此需要通过ParameterizedTypeReference
        assert popInStocks != null;
        //获取结果集
        Collection<PopInStock> collection = popInStocks.getContent();
        /** 2 **/
        Collection<PopInStock> recents = traverson.follow("pops","recents") //等价于follow("pops").follow("recents")
                .toObject(popInStocksType).getContent();
        /** 3 **/
        //获取对应的url
        String url = traverson.follow("pops").asLink().getHref();
        //再使用RestTemplate插入数据
        PopInStock popInStock = new PopInStock();
        popInStock.setName("Traverson");
        new RestTemplate().postForEntity(url,popInStock,PopInStock.class);
    }