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

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());

6.  

7. JSONObject param = new JSONObject();

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

9.  

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

11.  

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;

4.  

5. public LinkedMultiValueMap() {

6. this.targetMap = new LinkedHashMap();

7. }

8.  

9. public LinkedMultiValueMap(int initialCapacity) {

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

11. }

12.  

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

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

15. }

16.  

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. }

22.  

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. }

29.  

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. }

36.  

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

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

39.  

40. while(var2.hasNext()) {

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

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

43. }

44.  

45. }

46.  

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. }

52.  

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

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

55. }

56.  

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. }

63.  

64. });

65. return singleValueMap;

66. }

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