Java 保持POJO不变如何使用Jackson在JSON中注入新字段?
我的最终目标是,我有一个POJO列表。我需要使用Jackson将其转换为JSON字符串。当转换为JSON时。我需要再加几把钥匙。 为了做到这一点,我只有一个解决办法。如果我将POJO的列表转换为对象节点的列表,这样我就可以在对象节点中添加信息。之后,我将转换为JSON字符串Java 保持POJO不变如何使用Jackson在JSON中注入新字段?,java,json,serialization,jackson,pojo,Java,Json,Serialization,Jackson,Pojo,我的最终目标是,我有一个POJO列表。我需要使用Jackson将其转换为JSON字符串。当转换为JSON时。我需要再加几把钥匙。 为了做到这一点,我只有一个解决办法。如果我将POJO的列表转换为对象节点的列表,这样我就可以在对象节点中添加信息。之后,我将转换为JSON字符串 List dummyPOJO=getPOJO() ObjectNode ObjectNode=mapper.convertValue(dummyPOJO,newtypereference(){}) 此代码给出了一个follo
List dummyPOJO=getPOJO()代码>
ObjectNode ObjectNode=mapper.convertValue(dummyPOJO,newtypereference(){})代码>
此代码给出了一个follow错误
java.lang.ClassCastException:java.util.ArrayList不能强制转换为com.fasterxml.jackson.databind.node.ObjectNode
如果有任何解决方案,请告诉我。提前感谢:)以下代码似乎不正确
ObjectNode objectNode = mapper.convertValue(dummyPOJO, new TypeReference<List<ObjectNode>>(){});
现在将创建一些Person对象并将其转换为列表
结构
然后将迭代所有ObjectNode,并在Person ObjectNode中添加新的字段Sex
但POJO结构将保持不变
JSONListConverter.java
package sep2020;
import java.io.IOException;
import java.util.List;
import java.util.stream.Collectors;
import java.util.stream.Stream;
import com.fasterxml.jackson.core.type.TypeReference;
import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.SerializationFeature;
import com.fasterxml.jackson.databind.node.ObjectNode;
public class JSONListConverter {
public static void main(String[] args) throws IOException {
ObjectMapper objectMapper = new ObjectMapper();
objectMapper.enable(SerializationFeature.INDENT_OUTPUT);
// Define map which will be converted to JSON
List<Person> personList = Stream.of(new Person("A", "B", 34),
new Person("C", "D", 75), new Person("E", "F", 21),
new Person("G", "H", 55)).collect(Collectors.toList());
List<ObjectNode> objectNodes = objectMapper.convertValue(personList,
new TypeReference<List<ObjectNode>>() {
});
JsonNode jsonNode = objectMapper.convertValue(objectNodes,
JsonNode.class);
// Existing Json structure
System.out.println("Existing Json:\n"
+ objectMapper.writeValueAsString(jsonNode));
System.out.println("\n\n");
// Adding an extra field
if (objectNodes != null && objectNodes.size() > 0) {
for (ObjectNode objectNode : objectNodes) {
objectNode.put("Sex", "M");
}
}
jsonNode = objectMapper.convertValue(objectNodes, JsonNode.class);
// Updated Json structure
System.out.println("Updated Json:\n"
+ objectMapper.writeValueAsString(jsonNode));
}
}
List<ObjectNode> objectNodes = mapper.convertValue(dummyPOJO, new TypeReference<List<ObjectNode>>(){});
package sep2020;
public class Person {
public String firstName;
public String lastName;
public int age;
public Person() {
}
public Person(String firstName, String lastName, int age) {
this.firstName = firstName;
this.lastName = lastName;
this.age = age;
}
public String toString() {
return "[" + firstName + " " + lastName + " " + age + "]";
}
}
package sep2020;
import java.io.IOException;
import java.util.List;
import java.util.stream.Collectors;
import java.util.stream.Stream;
import com.fasterxml.jackson.core.type.TypeReference;
import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.SerializationFeature;
import com.fasterxml.jackson.databind.node.ObjectNode;
public class JSONListConverter {
public static void main(String[] args) throws IOException {
ObjectMapper objectMapper = new ObjectMapper();
objectMapper.enable(SerializationFeature.INDENT_OUTPUT);
// Define map which will be converted to JSON
List<Person> personList = Stream.of(new Person("A", "B", 34),
new Person("C", "D", 75), new Person("E", "F", 21),
new Person("G", "H", 55)).collect(Collectors.toList());
List<ObjectNode> objectNodes = objectMapper.convertValue(personList,
new TypeReference<List<ObjectNode>>() {
});
JsonNode jsonNode = objectMapper.convertValue(objectNodes,
JsonNode.class);
// Existing Json structure
System.out.println("Existing Json:\n"
+ objectMapper.writeValueAsString(jsonNode));
System.out.println("\n\n");
// Adding an extra field
if (objectNodes != null && objectNodes.size() > 0) {
for (ObjectNode objectNode : objectNodes) {
objectNode.put("Sex", "M");
}
}
jsonNode = objectMapper.convertValue(objectNodes, JsonNode.class);
// Updated Json structure
System.out.println("Updated Json:\n"
+ objectMapper.writeValueAsString(jsonNode));
}
}
Existing Json:
[ {
"firstName" : "A",
"lastName" : "B",
"age" : 34
}, {
"firstName" : "C",
"lastName" : "D",
"age" : 75
}, {
"firstName" : "E",
"lastName" : "F",
"age" : 21
}, {
"firstName" : "G",
"lastName" : "H",
"age" : 55
} ]
Updated Json:
[ {
"firstName" : "A",
"lastName" : "B",
"age" : 34,
"Sex" : "M"
}, {
"firstName" : "C",
"lastName" : "D",
"age" : 75,
"Sex" : "M"
}, {
"firstName" : "E",
"lastName" : "F",
"age" : 21,
"Sex" : "M"
}, {
"firstName" : "G",
"lastName" : "H",
"age" : 55,
"Sex" : "M"
} ]