Java对象转换成JSON String格式

JSON 格式转换成Java对象

标签（空格分隔）： Java jsckson

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源代码
添加依赖到pom.xml

<!-- https://mvnrepository.com/artifact/com.fasterxml.jackson.core/jackson-core -->
<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-databind</artifactId>
    <version>2.6.3</version>
</dependency>

需要转换的对象是ObjectC和ObjectD,其中ObjectD的一个成员变量是List<ObjectC>.
jackson能够递归转换,让json中包含json的这种也能够转为相应的Java对象

//ObjectC.java
package com.workstation;

import com.fasterxml.jackson.annotation.JsonProperty;

public class ObjectC {

    @JsonProperty ("Message")
    String message;

    public String getMessage() {
        return message;
    }

    public void setMessage(String message) {
        this.message = message;
    }

    //JSON 中message也会绑定到message成员变量
    @JsonProperty ("message")
    public String _getMessage() {
        return message;
    }

    @JsonProperty ("message")
    public void _setMessage(String message) {
        this.message = message;
    }

}

如上所写，ObjectC对象和Json中的”Message”和”message”都绑定到了message成员变量

//ObjectD.java
package com.workstation;

import java.util.List;

import com.fasterxml.jackson.annotation.JsonProperty;

public class ObjectD {

    List<ObjectC> list;

    @JsonProperty ("List")
    public List<ObjectC> getList() {
        return list;
    }

    //能够像spring一样,自动完成ObjectC的转换
    @JsonProperty ("List")
    public void setList(List<ObjectC> list) {
        this.list = list;
    }

}

测试代码

package com.workstation;

import java.io.IOException;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;

import org.junit.Test;

import com.fasterxml.jackson.core.JsonParseException;
import com.fasterxml.jackson.core.type.TypeReference;
import com.fasterxml.jackson.databind.JsonMappingException;
import com.fasterxml.jackson.databind.ObjectMapper;

public class testJsonToObject {

    @Test
    public void test() throws JsonParseException, JsonMappingException, IOException {
        String jsonString = "{    \"message\":\"Hello World\"}";
        ObjectC objectC = (new ObjectMapper()).readValue(jsonString, ObjectC.class);
        System.out.println(objectC.getMessage());


//      {
//          "List": [
//          {"message":"hello A"},
//          {"Message":"hello B"}
//          ]
//          }
        String jsonListString = "{\r\n" + 
                "\"List\": [\r\n" + 
                "{\"message\":\"hello A\"},\r\n" + 
                "{\"Message\":\"hello B\"}\r\n" + 
                "]\r\n" + 
                "}";
        ObjectD objectD = (new ObjectMapper()).readValue(jsonListString, ObjectD.class);
        List<ObjectC> list = objectD.getList();
        for(int i = 0; i < list.size(); ++i) {
            System.out.println(list.get(i).getMessage());
        }


        //jackson结合TypeReference
        Map<String, String> map = new HashMap<String, String>();
        map = (new ObjectMapper()).readValue(jsonString, new TypeReference<Map<String, String>>(){});
        for(Entry<String, String> entry : map.entrySet()) {
            System.out.println(entry.getKey()+":"+entry.getValue());
        }

    }

}


}

输出

Hello World
hello A
hello B
message:Hello World

如上所示,jackson成功读取了含有list的json对象
jsackson还可以和TypeReference一起使用,这样对某些特定情况下就不用专门新建一个类来读取相关东西了