Springboot使用RestTemplate发送Post请求postForEntity (application/json)的坑

当使用RestTemplate进行http请求时，的确很方便，但是当需要进行post请求时遇到了坑

1POST传递参数 ：采用 LinkedMultiValueMap ，不能使用HashMap

String url = 'http://posturl'; MultiValueMap 
  
    map= new LinkedMultiValueMap 
   
     (); map.add("shopid","1"); HttpHeaders headers = new HttpHeaders(); headers.setContentType(MediaType.APPLICATION_FORM_URLENCODED); HttpEntity 
    
      > request = new HttpEntity 
     
       >(map, headers); return restTemplate.postForEntity(url, request,String.class); 
      
     
    
  

• 注意 上面的请求支持参数类型均为String类型，如果MultiValueMap
  
   LinkedMultiValueMap 会将value放进list中，key –> [value]
  

2 采用JSONObject或者实体类传递参数

 RestTemplate restTemplate = new RestTemplate(); HttpHeaders headers = new HttpHeaders(); MediaType type = MediaType.parseMediaType("application/json; charset=UTF-8"); headers.setContentType(type); headers.add("Accept", MediaType.APPLICATION_JSON.toString()); JSONObject param = new JSONObject(); param.put("username", "123"); HttpEntity 
  
    formEntity = new HttpEntity 
   
     (param.toString(), headers); String result = restTemplate.postForObject(url, formEntity, String.class); 
    
  

• 使用这种方式可以传递任意类型的参数，避免上面的情况

总结，遇到这种问题时多看看源码会很有帮助。

public class LinkedMultiValueMap 
  
    implements MultiValueMap 
   
     , Serializable, Cloneable { private static final long serialVersionUID = L; private final Map 
    
      > targetMap; public LinkedMultiValueMap() { this.targetMap = new LinkedHashMap(); } public LinkedMultiValueMap(int initialCapacity) { this.targetMap = new LinkedHashMap(initialCapacity); } public LinkedMultiValueMap(Map 
     
       > otherMap) { this.targetMap = new LinkedHashMap(otherMap); } @Nullable public V getFirst(K key) { List 
      
        values = (List)this.targetMap.get(key); return values != null && !values.isEmpty() ? values.get(0) : null; } public void add(K key, @Nullable V value) { List 
       
         values = (List)this.targetMap.computeIfAbsent(key, (k) -> { return new LinkedList(); }); values.add(value); } public void addAll(K key, List 
         values) { List 
        
          currentValues = (List)this.targetMap.computeIfAbsent(key, (k) -> { return new LinkedList(); }); currentValues.addAll(values); } public void addAll(MultiValueMap 
         
           values) { Iterator var2 = values.entrySet().iterator(); while(var2.hasNext()) { Entry 
          
            > entry = (Entry)var2.next(); this.addAll(entry.getKey(), (List)entry.getValue()); } } public void set(K key, @Nullable V value) { List 
           
             values = new LinkedList(); values.add(value); this.targetMap.put(key, values); } public void setAll(Map 
            
              values) { values.forEach(this::set); } public Map 
             
               toSingleValueMap() { LinkedHashMap 
              
                singleValueMap = new LinkedHashMap(this.targetMap.size()); this.targetMap.forEach((key, values) -> { if (values != null && !values.isEmpty()) { singleValueMap.put(key, values.get(0)); } }); return singleValueMap; }