json转换之gson

工具类，有待以后复用

jar包依赖

<!-- https://mvnrepository.com/artifact/com.google.code.gson/gson -->
	<dependency>
	    <groupId>com.google.code.gson</groupId>
	    <artifactId>gson</artifactId>
	    <version>2.8.2</version>
	</dependency>

package info.lumanman.GsonUtil;

import java.io.FileReader;
import java.lang.reflect.Type;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import com.google.gson.Gson;
import com.google.gson.internal.LinkedTreeMap;
import com.google.gson.reflect.TypeToken;

public class GsonUtil {

	private final static Gson gson=new Gson();
    private GsonUtil() {

    }
    public static Gson getInstance(){
        return gson;
    }
    /**
     * javaBean、列表、数组、转换为json字符串
     */
    public static String obj2json(Object obj) throws Exception {
        return gson.toJson(obj, Object.class);
    }

    /**
     *  json 转JavaBean、Map
     */

    public static <T> T json2pojo(String jsonString,Class<T> clazz) throws Exception {

        return gson.fromJson(jsonString,clazz);
    }



	/**
     *  json字符串转换为同类型的value-->map
     */
    public static <T> Map<String, T> json2map(String jsonString, Class<T> clazz) throws Exception {
    	Type type = new TypeToken<Map<String,LinkedTreeMap<String, T>>>() {}.getType();
    	Map<String,LinkedTreeMap<String, T>> map=gson.fromJson(jsonString, type);
        Map<String,T> result=new HashMap<String, T>();
        for(Map.Entry<String,LinkedTreeMap<String, T>> entry:map.entrySet()){
            result.put(entry.getKey(),json2pojo(obj2json(entry.getValue()), clazz));
        }
        return result;
    }

    /**
     *  与javaBean json数组字符串转换为列表
     */
    public static <T> List<T> json2list(String jsonString,Class<T> clazz) throws Exception {
        Type type = new TypeToken<ArrayList<LinkedTreeMap<String, T>>>() {}.getType();
        ArrayList<LinkedTreeMap<String, T>> sList=gson.fromJson(jsonString, type);
        List<T> result=new ArrayList<T>();
        for(LinkedTreeMap<String, T> map:sList){
            result.add(json2pojo(obj2json(map), clazz));
        }
        return result;

    }


    /**
     * json 转List<LinkedHashMap<String,Object>>
     * @param map
     * @return
     */
    public static List<LinkedTreeMap<String,Object>> json2listMap(String json) {

        List<LinkedTreeMap<String,Object>> list = new ArrayList<LinkedTreeMap<String,Object>>();
        list =   gson.fromJson(json, List.class);

        return list;
    }
    
    /**
     * json文件 转pojo
     * 注意这里的file文件最好是新建的notepadd++，并保存为UTF-8的文件，防止乱码
     * @param map
     * @return
     */
    public static <T> T file2pojo(FileReader fileReader ,Class<T> clazz) {
          return gson.fromJson(fileReader, clazz);

    }
}

package info.lumanman.GsonUtil;

import java.io.File;
import java.io.FileReader;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;

import org.junit.Test;

import com.google.gson.internal.LinkedTreeMap;

import info.lumanman.JacksonUtil.JacksonUtil;
import info.lumanman.JacksonUtil.School;
import info.lumanman.JacksonUtil.Student;

public class GsonTest {

	/**
     * javaBean、列表、数组、Map转换为json字符串
     */
	@Test
	public void obj2jsonTest() throws Exception {
		School school=new School();
		school.setAddress("安徽");
		school.setName("圣泉中学");
		
		Student student=new Student();
		student.setAge(18);
		student.setName("张三");
		
		Student student2=new Student();
		student2.setAge(18);
		student2.setName("张三");
		
		List<Student> list=new ArrayList<Student>();
		list.add(student);
		list.add(student2);
		school.setStudentList(list);
		
		String json=GsonUtil.obj2json(school);
		System.out.println(json);
	}
	
	/**
     *  json 转JavaBean、Map
     */
	@Test
	public void json2pojoTest() throws Exception {
		String jsonString="{\"a\": 0,"+
							"\"name\": \"圣泉中学\","+
							"\"address\": \"安徽\","+
							"\"createdDate\": null,"+
							"\"studentList\": [{"+
								"\"name\": \"张三\","+
								"\"age\": 18"+
							"},"+
							"{"+
								"\"name\": \"张三\","+
								"\"age\": 18}]}";
		
		Map<String, Object> map=GsonUtil.json2pojo(jsonString,Map.class);
		System.out.println(map);
	}
	
	/**
     *  json字符串转换为map
     */
	@Test
	public void json2mapClassTest() throws Exception {
		String jsonString="{\"student\": {"+
					"\"name\": \"张三\","+
					"\"age\": 18}}";
		
		Map<String, Student> map=GsonUtil.json2map(jsonString,Student.class);
		System.out.println(map.get("student").getAge());
	}
	
	/**
     *  与javaBean json数组字符串转换为列表
     */
	@Test
	public void json2listTest() throws Exception {
		String jsonString="[{\"name\": \"张三\","+
					"\"age\": 18"+
				"},"+
				"{"+
					"\"name\": \"张三\","+
					"\"age\": 18}]";
		
		List<Student> studentList=GsonUtil.json2list(jsonString,Student.class);
		System.out.println(studentList.get(0).getAge());
	}
	
	/**
     * json 转List<LinkedHashMap<String,Object>>
     * @param map
     * @return
     */
	@Test
	public void json2listMapTest() throws Exception {
		String jsonString="[{"+
					"\"name\": \"张三\","+
					"\"age\": 18"+
				"},"+
				"{"+
					"\"name\": \"张三\","+
					"\"age\": 18}]";
		
		List<LinkedTreeMap<String, Object>> list=GsonUtil.json2listMap(jsonString);
		System.out.println(list.get(0).get("name"));
	}
	
	/**
     * json文件 转pojo
     * 注意这里的file文件最好是新建的notepadd++，并保存为UTF-8的文件，防止乱码
     * @param map
     * @return
     */
	@Test
	public void file2pojoTest() throws Exception {
		File file=new File("C:\\Users\\WM\\Desktop\\utf-8报文.txt");
		School school=GsonUtil.file2pojo(new FileReader(file),School.class);
		System.out.println(school);
	}
	
}

package info.lumanman.JacksonUtil;

import java.io.Serializable;
import java.util.Date;
import java.util.List;

public class School implements Serializable{

	private int a;
	private String name;
	
	private String address;
	
	private Date createdDate;
	
	private List<Student> studentList;
	
	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}

	public String getAddress() {
		return address;
	}

	public void setAddress(String address) {
		this.address = address;
	}

	public List<Student> getStudentList() {
		return studentList;
	}

	public void setStudentList(List<Student> studentList) {
		this.studentList = studentList;
	}

	public Date getCreatedDate() {
		return createdDate;
	}

	public void setCreatedDate(Date createdDate) {
		this.createdDate = createdDate;
	}

	public int getA() {
		return a;
	}

	public void setA(int a) {
		this.a = a;
	}

	@Override
	public String toString() {
		return "School [a=" + a + ", name=" + name + ", address=" + address + ", createdDate=" + createdDate
				+ ", studentList=" + studentList + "]";
	}
	
	
}

package info.lumanman.JacksonUtil;

public class Student {

	private String name;
	
	private int age;

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}

	public int getAge() {
		return age;
	}

	public void setAge(int age) {
		this.age = age;
	}

	@Override
	public String toString() {
		return "Student [name=" + name + ", age=" + age + "]";
	}
	
	
}

UTF-8文件内容

{
	"a": 0,
	"name": "圣泉中学",
	"address": "安徽",
	"createdDate": null,
	"studentList": [{
		"name": "张三",
		"age": 18
	},
	{
		"name": "张三",
		"age": 18
	}]
}