博客

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

1. 
String url = 'http://posturl';


2. 
MultiValueMap<String, String> map= new LinkedMultiValueMap<String, String>();


3. 
map.add("shopid","1");


4. 
HttpHeaders headers = new HttpHeaders();


5. 
headers.setContentType(MediaType.APPLICATION_FORM_URLENCODED);


6. 
HttpEntity<MultiValueMap<String, String>> request = new HttpEntity<MultiValueMap<String, String>>(map, headers);


7. 
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<String, Object>  LinkedMultiValueMap 会将value放进list中，key –> [value]

2 采用JSONObject或者实体类传递参数

1. 
RestTemplate restTemplate = new RestTemplate();


2. 
HttpHeaders headers = new HttpHeaders();


3. 
MediaType type = MediaType.parseMediaType("application/json; charset=UTF-8");


4. 
headers.setContentType(type);


5. 
headers.add("Accept", MediaType.APPLICATION_JSON.toString());


7. 
JSONObject param = new JSONObject();


8. 
param.put("username", "123");


10. 
HttpEntity<String> formEntity = new HttpEntity<String>(param, headers);


12. 
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。

1. 
public class LinkedMultiValueMap<K, V> implements MultiValueMap<K, V>, Serializable, Cloneable {



2. 
private static final long serialVersionUID = 3801124242820219131L;


3. 
private final Map<K, List<V>> targetMap;


5. 
public LinkedMultiValueMap() {



6. 
this.targetMap = new LinkedHashMap();


7. 
}


9. 
public LinkedMultiValueMap(int initialCapacity) {



10. 
this.targetMap = new LinkedHashMap(initialCapacity);


11. 
}


13. 
public LinkedMultiValueMap(Map<K, List<V>> otherMap) {



14. 
this.targetMap = new LinkedHashMap(otherMap);


15. 
}


17. 
@Nullable


18. 
public V getFirst(K key) {



19. 
List<V> values = (List)this.targetMap.get(key);


20. 
return values != null && !values.isEmpty() ? values.get(0) : null;


21. 
}


23. 
public void add(K key, @Nullable V value) {



24. 
List<V> values = (List)this.targetMap.computeIfAbsent(key, (k) -> {



25. 
return new LinkedList();


26. 
});


27. 
values.add(value);


28. 
}


30. 
public void addAll(K key, List<? extends V> values) {



31. 
List<V> currentValues = (List)this.targetMap.computeIfAbsent(key, (k) -> {



32. 
return new LinkedList();


33. 
});


34. 
currentValues.addAll(values);


35. 
}


37. 
public void addAll(MultiValueMap<K, V> values) {



38. 
Iterator var2 = values.entrySet().iterator();


40. 
while(var2.hasNext()) {



41. 
Entry<K, List<V>> entry = (Entry)var2.next();


42. 
this.addAll(entry.getKey(), (List)entry.getValue());


43. 
}


45. 
}


47. 
public void set(K key, @Nullable V value) {



48. 
List<V> values = new LinkedList();


49. 
values.add(value);


50. 
this.targetMap.put(key, values);


51. 
}


53. 
public void setAll(Map<K, V> values) {



54. 
values.forEach(this::set);


55. 
}


57. 
public Map<K, V> toSingleValueMap() {



58. 
LinkedHashMap<K, V> singleValueMap = new LinkedHashMap(this.targetMap.size());


59. 
this.targetMap.forEach((key, values) -> {



60. 
if (values != null && !values.isEmpty()) {



61. 
singleValueMap.put(key, values.get(0));


62. 
}


64. 
});


65. 
return singleValueMap;


66. 
}


转自：

https://blog.csdn.net/justin_bob/article/details/103019115