源代码：
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public <T> T convertValue(Object fromValue, TypeReference<?> toValueTypeRef) throws IllegalArgumentException { return (T) _convert(fromValue, _typeFactory.constructType(toValueTypeRef)); } |
该方法用于用jackson将bean转换为map
例子：
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List<SObject> sObjects = new ObjectMapper().convertValue(map.get( "list" ), new TypeReference<List<SObject>>() { }); |
微服务中从其他服务获取过来的对象，如果从Object强转为自定义的类型会报错，利用ObjectMapper转换。
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ObjectMapper mapper = new ObjectMapper(); DefaultResponse defaultResponse = proxy.getData(); List<Resource> resources = (<Resource>) defaultResponse.getData(); //这里的场景是：data是一个Object类型的，但是它其实是一个List<Resouce>，想把List中的每个对象分别转成可用的对象 for ( int i = 0 ; i < serviceDateResources.size(); i++) { Resource resource = mapper.convertValue(resources.get(i), Resource. class ); //经过这步处理，resource就是可用的类型了，如果不转化会报错 } |
在转换过程中有些属性被设置为空，这样就不需要转化
处理方法：
在需要转化的实体类商添加如下注解
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@JsonInclude (Include.NON_NULL) @JsonInclude (Include.Include.ALWAYS) 默认 @JsonInclude (Include.NON_DEFAULT) 属性为默认值不序列化 @JsonInclude (Include.NON_EMPTY) 属性为 空（[]） 或者为 NULL 都不序列化 @JsonInclude (Include.NON_NULL) 属性为NULL 不序列化 |
jackson objectMapper json字符串、对象bean、map、数组list互相转换常用的方法列举：
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ObjectMapper mapper = new ObjectMapper(); |
1.对象转json字符串
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User user= new User(); String userJson=mapper.writeValueAsString(user); |
2.Map转json字符串
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Map map= new HashMap(); String json=mapper.writeValueAsString(map); |
3.数组list转json字符串
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Student[] stuArr = {student1, student3}; String jsonfromArr = mapper.writeValueAsString(stuArr); |
4.json字符串转对象
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String expected = "{\"name\":\"Test\"}" ; User user = mapper.readValue(expected, User. class ); |
5.json字符串转Map
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String expected = "{\"name\":\"Test\"}" ; Map userMap = mapper.readValue(expected, Map. class ); |
6.json字符串转对象数组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字符串转Map数组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默认将对象转换为LinkedHashMap：
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String expected = "[{\"name\":\"Ryan\"},{\"name\":\"Test\"},{\"name\":\"Leslie\"}]" ; ArrayList arrayList = mapper.readValue(expected, ArrayList. class ); |
9.json字符串与list或map互转的方法
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ObjectMapper objectMapper = new ObjectMapper(); //遇到date按照这种格式转换 SimpleDateFormat fmt = new SimpleDateFormat( "yyyy-MM-dd HH:mm:ss" ); objectMapper.setDateFormat(fmt);
String preference = "{name:'侯勇'}" ; //json字符串转map Map<String, String> preferenceMap = new HashMap<String, String>(); preferenceMap = objectMapper.readValue(preference, preferenceMap.getClass());
//map转json字符串 String result=objectMapper.writeValueAsString(preferenceMap); |
10.bean转换为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将bean转换为map returnList=mapper.convertValue(menuList, new TypeReference<List<Map<String, String>>>(){}); |
objectMapper.convertValue() 报错
报错信息如下：
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]])
根据以上报错得知, 是java.time.LocalDateTime类型的原因. ObjectMapper 不能对LocalDateTime 序列化. 加上以下注解即可解决
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@JsonDeserialize (using = LocalDateTimeDeserializer. class ) @JsonSerialize (using = LocalDateTimeSerializer. class ) |
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@ApiModelProperty (value = "创建时间" ) @JsonDeserialize (using = LocalDateTimeDeserializer. class ) @JsonSerialize (using = LocalDateTimeSerializer. class ) private LocalDateTime createTime; |
以上为个人经验，希望能给大家一个参考，也希望大家多多支持。
原文链接：https://blog.csdn.net/weixin_39778417/article/details/103304940
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