jackson中的tree model例子

今天继续jackson的学习,在JACKSON中,可以用TREE MODEL树型结构,象以DOM
的方式那样去读取结点,方法为:
  ObjectMapper mapper = new ObjectMapper();
 

BufferedReader fileReader = new BufferedReader(
new FileReader("c:\\user.json"));
JsonNode rootNode = mapper.readTree(fileReader);
  JsonNode nameNode = rootNode.path("name");
System.out.println(nameNode.getTextValue());


比如一个user.json如下:
  {
  "age" : 29,
  "messages" : [ "msg 1", "msg 2", "msg 3" ],
  "name" : "mkyong"
 }
下面一个完整的的例子演示了读取和修改结点
 [code="java"]
import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;
import java.io.IOException;
import java.util.Iterator;
 
import org.codehaus.jackson.JsonGenerationException;
import org.codehaus.jackson.JsonNode;
import org.codehaus.jackson.map.JsonMappingException;
import org.codehaus.jackson.map.ObjectMapper;
import org.codehaus.jackson.node.ObjectNode;
 
public class JacksonTreeNodeExample {
public static void main(String[] args) {
 
ObjectMapper mapper = new ObjectMapper();
 
try {
 
BufferedReader fileReader = new BufferedReader(
new FileReader("c:\\user.json"));
JsonNode rootNode = mapper.readTree(fileReader);
 
/*** read ***/
JsonNode nameNode = rootNode.path("name");
System.out.println(nameNode.getTextValue());
 
JsonNode ageNode = rootNode.path("age");
System.out.println(ageNode.getIntValue());
 
JsonNode msgNode = rootNode.path("messages");
Iterator<JsonNode> ite = msgNode.getElements();
 
while (ite.hasNext()) {
JsonNode temp = ite.next();
System.out.println(temp.getTextValue());
 
}
 
/*** update ***/
((ObjectNode)rootNode).put("nickname", "new nickname");
((ObjectNode)rootNode).put("name", "updated name");
((ObjectNode)rootNode).remove("age");
 
mapper.writeValue(new File("c:\\user.json"), rootNode);
 
} catch (JsonGenerationException e) {
 
e.printStackTrace();
 
} catch (JsonMappingException e) {
 
e.printStackTrace();
 
} catch (IOException e) {
 
e.printStackTrace();
 
}
 
}


[/code]


输出:
mkyong
29
msg 1
msg 2
msg 3


 并且这里修改了节点内容,重新写了新的JSON,所以新的JSON文件为:
{
  "messages" : [ "msg 1", "msg 2", "msg 3" ],
  "name" : "updated name",
  "nickname" : "new nickname"
}