jackson中的写和解析JSON的api例子

本次介绍的是在jackson中,如何去写和解析json,其中用到的都是jackson自己的

流的API.

1 JACKSON中写一个json文件使用的是JsonGenerator类,

import java.io.File;

import java.io.IOException;

import org.codehaus.jackson.JsonEncoding;

import org.codehaus.jackson.JsonFactory;

import org.codehaus.jackson.JsonGenerationException;

import org.codehaus.jackson.JsonGenerator;

import org.codehaus.jackson.map.JsonMappingException;

 

public class JacksonStreamExample {

   public static void main(String[] args) {

 

     try {

 

JsonFactory jfactory = new JsonFactory();

 

/*** write to file ***/

JsonGenerator jGenerator = jfactory.createJsonGenerator(new File(

"c:\\user.json"), JsonEncoding.UTF8);

jGenerator.writeStartObject(); // {

 

jGenerator.writeStringField("name", "mkyong"); // "name" : "mkyong"

jGenerator.writeNumberField("age", 29); // "age" : 29

 

jGenerator.writeFieldName("messages"); // "messages" :

jGenerator.writeStartArray(); // [

 

jGenerator.writeString("msg 1"); // "msg 1"

jGenerator.writeString("msg 2"); // "msg 2"

jGenerator.writeString("msg 3"); // "msg 3"

 

jGenerator.writeEndArray(); // ]

 

jGenerator.writeEndObject(); // }

 

jGenerator.close();

 

     } catch (JsonGenerationException e) {

 

e.printStackTrace();

 

     } catch (JsonMappingException e) {

 

e.printStackTrace();

 

     } catch (IOException e) {

 

e.printStackTrace();

 

     }

 

   }

 

}

输出为:

{

"name":"mkyong",

"age":29,

"messages":["msg 1","msg 2","msg 3"]

}

2 解析JSON

我们把上面输出的JSON文件重新读取出来,再解析, 注意在json中,解析是以TOKEN方式进行的,比如:

{

"name":"mkyong"

}

将为解析为:

Token 1 = “{“

Token 2 = “name”

Token 3 = “mkyong”

Token 4 = “}”

代码:

import java.io.File;

import java.io.IOException;

import org.codehaus.jackson.JsonFactory;

import org.codehaus.jackson.JsonGenerationException;

import org.codehaus.jackson.JsonParser;

import org.codehaus.jackson.JsonToken;

import org.codehaus.jackson.map.JsonMappingException;

 

public class JacksonStreamExample {

   public static void main(String[] args) {

 

     try {

 

JsonFactory jfactory = new JsonFactory();

 

/*** read from file ***/

JsonParser jParser = jfactory.createJsonParser(new File("c:\\user.json"));

 

// loop until token equal to "}"

while (jParser.nextToken() != JsonToken.END_OBJECT) {

 

String fieldname = jParser.getCurrentName();

if ("name".equals(fieldname)) {

 

 

                  //当前结点为name 

 jParser.nextToken();

 System.out.println(jParser.getText()); // 输出 mkyong

 

}

 

if ("age".equals(fieldname)) {

 

 // 当前结点为age 

                  // move to next, which is "name"'s value

 jParser.nextToken();

 System.out.println(jParser.getIntValue()); // display 29

 

}

 

if ("messages".equals(fieldname)) {

 

 jParser.nextToken(); 

 while (jParser.nextToken() != JsonToken.END_ARRAY) {

 

                     // display msg1, msg2, msg3

    System.out.println(jParser.getText()); 

 

 }

 

}

 

 }

 jParser.close();

 

     } catch (JsonGenerationException e) {

 

 e.printStackTrace();

 

     } catch (JsonMappingException e) {

 

 e.printStackTrace();

 

     } catch (IOException e) {

 

 e.printStackTrace();

 

     }

 

  }

 

}

最后输出:

mkyong

29

msg 1

msg 2

msg 3