源代碼：
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public <T> T convertValue(Object fromValue, TypeReference<?> toValueTypeRef) throws IllegalArgumentException { return (T) _convert(fromValue, _typeFactory.constructType(toValueTypeRef)); } |
該方法用于用jackson將bean轉換為map
例子：
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List<SObject> sObjects = new ObjectMapper().convertValue(map.get("list"), new TypeReference<List<SObject>>() { }); |
微服務中從其他服務獲取過來的對象，如果從Object強轉為自定義的類型會報錯，利用ObjectMapper轉換。
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ObjectMapper mapper = new ObjectMapper();DefaultResponse defaultResponse = proxy.getData();List<Resource> resources = (<Resource>) defaultResponse.getData(); //這里的場景是：data是一個Object類型的，但是它其實是一個List<Resouce>，想把List中的每個對象分別轉成可用的對象for (int i = 0; i < serviceDateResources.size(); i++) { Resource resource = mapper.convertValue(resources.get(i), Resource.class); //經過這步處理，resource就是可用的類型了，如果不轉化會報錯} |
在轉換過程中有些屬性被設置為空，這樣就不需要轉化
處理方法：
在需要轉化的實體類商添加如下注解
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@JsonInclude(Include.NON_NULL) @JsonInclude(Include.Include.ALWAYS) 默認 @JsonInclude(Include.NON_DEFAULT) 屬性為默認值不序列化 @JsonInclude(Include.NON_EMPTY) 屬性為 空（“”） 或者為 NULL 都不序列化 @JsonInclude(Include.NON_NULL) 屬性為NULL 不序列化 |
jackson objectMapper json字符串、對象bean、map、數組list互相轉換常用的方法列舉：
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ObjectMapper mapper = new ObjectMapper(); |
1.對象轉json字符串
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User user=new User();String userJson=mapper.writeValueAsString(user); |
2.Map轉json字符串
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Map map=new HashMap(); String json=mapper.writeValueAsString(map); |
3.數組list轉json字符串
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Student[] stuArr = {student1, student3}; String jsonfromArr = mapper.writeValueAsString(stuArr); |
4.json字符串轉對象
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String expected = "{\"name\":\"Test\"}";User user = mapper.readValue(expected, User.class); |
5.json字符串轉Map
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String expected = "{\"name\":\"Test\"}";Map userMap = mapper.readValue(expected, Map.class); |
6.json字符串轉對象數組List
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String expected="[{\"a\":12},{\"b\":23},{\"name\":\"Ryan\"}]";CollectionType listType = mapper.getTypeFactory().constructCollectionType(ArrayList.class, User.class);List<User> userList = mapper.readValue(expected, listType); |
7.json字符串轉Map數組List<Map<String,Object>>
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String expected="[{\"a\":12},{\"b\":23},{\"name\":\"Ryan\"}]";CollectionType listType = mapper.getTypeFactory().constructCollectionType(ArrayList.class, Map.class);List<Map<String,Object>> userMapList = mapper.readValue(expected, listType); |
8.jackson默認將對象轉換為LinkedHashMap：
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String expected = "[{\"name\":\"Ryan\"},{\"name\":\"Test\"},{\"name\":\"Leslie\"}]";ArrayList arrayList = mapper.readValue(expected, ArrayList.class); |
9.json字符串與list或map互轉的方法
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ObjectMapper objectMapper = new ObjectMapper(); //遇到date按照這種格式轉換 SimpleDateFormat fmt = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"); objectMapper.setDateFormat(fmt); String preference = "{name:'侯勇'}"; //json字符串轉map Map<String, String> preferenceMap = new HashMap<String, String>(); preferenceMap = objectMapper.readValue(preference, preferenceMap.getClass()); //map轉json字符串 String result=objectMapper.writeValueAsString(preferenceMap); |
10.bean轉換為map
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List<Map<String,String>> returnList=new ArrayList<Map<String,String>>();List<Menu> menuList=menuDAOImpl.findByParentId(parentId);ObjectMapper mapper = new ObjectMapper();//用jackson將bean轉換為mapreturnList=mapper.convertValue(menuList,new TypeReference<List<Map<String, String>>>(){}); |
objectMapper.convertValue() 報錯
報錯信息如下：
com.fasterxml.jackson.databind.exc.InvalidDefinitionException: Cannot construct instance of java.time.LocalDateTime (no Creators, like default constructor, exist): cannot deserialize from Object value (no delegate- or property-based Creator) at [Source: UNKNOWN; line: -1, column: -1] (through reference chain: net.too1.tplus.user.user.entity.User[“createTime”])
根據以上報錯得知, 是java.time.LocalDateTime類型的原因. ObjectMapper 不能對LocalDateTime 序列化. 加上以下注解即可解決
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@JsonDeserialize(using = LocalDateTimeDeserializer.class)@JsonSerialize(using = LocalDateTimeSerializer.class) |
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@ApiModelProperty(value = "創建時間")@JsonDeserialize(using = LocalDateTimeDeserializer.class)@JsonSerialize(using = LocalDateTimeSerializer.class)private LocalDateTime createTime; |
以上為個人經驗，希望能給大家一個參考，也希望大家多多支持服務器之家。
原文鏈接：https://blog.csdn.net/weixin_39778417/article/details/103304940
