zoukankan      html  css  js  c++  java
  • java jackson map2json的使用

    How to convert Java Map to / from JSON (Jackson)

    Published: August 11, 2011 , Updated: August 11, 2011 , Author: mkyong

    In last Jackson example, we show you how to convert user define object to / from JSON data. This time, we are doing the same, but replace user define object with Map.

    Map is more suitable in a simple and short JSON processing, for complex JSON structure, you should always create an user defined object for easy maintainability.

    In this tutorial, we show you how to use Map to construct the JSON data, write it to file. And also how to read JSON from file, and display each value via Map.

    1. Write JSON to file

    Jackson example to use Map to construct the entire JSON data structure, then write it to file named “user.json“.

    import java.io.File;
    import java.io.IOException;
    import java.util.ArrayList;
    import java.util.HashMap;
    import java.util.List;
    import java.util.Map;
    import org.codehaus.jackson.JsonGenerationException;
    import org.codehaus.jackson.map.JsonMappingException;
    import org.codehaus.jackson.map.ObjectMapper;
     
    public class JacksonExample {
         public static void main(String[] args) {
     
    	ObjectMapper mapper = new ObjectMapper();
     
    	Map<String, Object> userInMap = new HashMap<String, Object>();
    	userInMap.put("name", "mkyong");
    	userInMap.put("age", 29);
     
    	List<Object> list = new ArrayList<Object>();
    	list.add("msg 1");
    	list.add("msg 2");
    	list.add("msg 3");
     
    	userInMap.put("messages", list);
     
    	try {
     
    	  // write JSON to a file
    	  mapper.writeValue(new File("c:\\user.json"), userInMap);
     
    	} catch (JsonGenerationException e) {
    	  e.printStackTrace();
    	} catch (JsonMappingException e) {
    	  e.printStackTrace();
    	} catch (IOException e) {
    	  e.printStackTrace();
    	}
         }
    }

    Outputuser.json

    {
    	"age":29,
    	"name":"mkyong",
    	"messages":["msg 1","msg 2","msg 3"]
    }

    2. Read JSON from file

    Read JSON data from file, convert it to Map and display the values.

    import java.io.File;
    import java.io.IOException;
    import java.util.ArrayList;
    import java.util.Map;
    import org.codehaus.jackson.JsonGenerationException;
    import org.codehaus.jackson.map.JsonMappingException;
    import org.codehaus.jackson.map.ObjectMapper;
    import org.codehaus.jackson.type.TypeReference;
     
    public class JacksonExample {
         public static void main(String[] args) {
     
    	ObjectMapper mapper = new ObjectMapper();
     
    	try {
     
    	   // read JSON from a file
    	   Map<String, Object> userInMap = mapper.readValue(
    		new File("c:\\user.json"), 
    		new TypeReference<Map<String, Object>>() {});
     
    	   System.out.println(userInMap.get("name"));
    	   System.out.println(userInMap.get("age"));
     
    	   ArrayList<String> list = 
    		(ArrayList<String>) userInMap.get("messages");
     
    	   for (String msg : list) {
    		System.out.println(msg);
    	   }
     
    	} catch (JsonGenerationException e) {
        	   e.printStackTrace();
    	} catch (JsonMappingException e) {
    	   e.printStackTrace();
    	} catch (IOException e) {
    	   e.printStackTrace();
    	}
         }
    }

    Output

    mkyong
    29
    msg 1
    msg 2
    msg 3

    References

  • 相关阅读:
    端口
    log4j常用配置以及日志文件保存位置
    jbpm node signal
    JBPM3.2 TABLE
    JBPM TaskInstance 对象创建过程
    【转】链接脚本
    快速平方根倒数
    GPS开发之知识储备(NMEA0183)
    HEX文件格式和其校验算法
    NRF51822之IIC(MEMS_LIS2DH12)
  • 原文地址:https://www.cnblogs.com/lexus/p/2406355.html
Copyright © 2011-2022 走看看