Jackson转换java对象与json对象

水深无声 2022-05-28 06:11 202阅读 0赞

本文转载自：http://www.cnblogs.com/songzhen/p/5794494.html

一、导入jar包：

（因为之前使用的是jackson 1.x的jar包，所以在把json转换成list时候没有objectMapper.getTypeFactory()这个方法，而使用jackson 2.x的jar包会有）

jackson 1.x：jackson-all-1.7.6.jar（1个核心文件）

jackson 2.x：jackson-annotations-2.5.0.jar、jackson-core-2.5.0.jar、jackson-databind-2.5.0.jar（3个核心文件）

二、建立java对象User：

![ExpandedBlockStart.gif][]

![复制代码][copycode.gif]

package com.cn.jackson.entity;
    
    public class User {
    
        private String name;
        
        private Integer age;
        
        private String address;
    
        public User(){
            
        }
        
        public User(String name, Integer age, String address) {
            super();
            this.name = name;
            this.age = age;
            this.address = address;
        }
    
        public String getName() {
            return name;
        }
    
        public void setName(String name) {
            this.name = name;
        }
    
        public Integer getAge() {
            return age;
        }
    
        public void setAge(Integer age) {
            this.age = age;
        }
    
        public String getAddress() {
            return address;
        }
    
        public void setAddress(String address) {
            this.address = address;
        }
        
        
    }

![复制代码][copycode.gif]

三、测试jackson 2.x的使用方法：

![复制代码][copycode.gif]

package com.cn.jackson.test;
    
    import java.io.IOException;
    import java.util.ArrayList;
    import java.util.HashMap;
    import java.util.List;
    import java.util.Map;
    
    import com.cn.jackson.entity.User;
    import com.fasterxml.jackson.core.JsonEncoding;
    import com.fasterxml.jackson.core.JsonGenerator;
    import com.fasterxml.jackson.databind.JavaType;
    import com.fasterxml.jackson.databind.ObjectMapper;
    
    public class Test_2_x {
        
        public static void main(String[] args) {
    
            try {
                ObjectMapper objectMapper = new ObjectMapper();
                JsonGenerator jsonGenerator = objectMapper.getJsonFactory()
                        .createJsonGenerator(System.out, JsonEncoding.UTF8);
                
                //对象转JSON
                User user = new User("张三", 23, "深圳市");
                System.out.println("ObjectMapper方式");
                objectMapper.writeValue(System.out, user);//直接输出到控制台
                String userJsonStr = objectMapper.writeValueAsString(user);//返回字符串，输出
                System.out.println(userJsonStr);
                System.out.println("JsonGenerator方式");
                jsonGenerator.writeObject(user);
                System.out.println();
                
                //map转JSON
                Map<String , Object> map = new HashMap<String ,Object>();
                map.put("one", new User("张", 12, "深圳"));
                map.put("two", new User("李", 22, "武汉"));
                map.put("three", new User("王", 32, "北京"));
                System.out.println("ObjectMapper方式");
                objectMapper.writeValue(System.out, map);
                //JsonGenerator方式同上
                
                //list转JSON
                List<User> list = new ArrayList<User>();
                list.add(new User("张", 12, "深圳"));
                list.add(new User("李", 22, "武汉"));
                list.add(new User("王", 32, "北京"));
                System.out.println("ObjectMapper方式");
                objectMapper.writeValue(System.out, list);
                //JsonGenerator方式同上
                
                //JSON转java对象：
                String json = "{\"name\":\"张三\",\"age\":23,\"address\":\"深圳市\"}";
                User zhang = objectMapper.readValue(json, User.class);
                System.out.println(zhang.getName()+"\n"+zhang.getAge()+"\n"+zhang.getAddress());
                
                //JSON转list
                String listJson = "[{\"name\":\"张三\",\"age\":21,\"address\":\"深圳\"},"
                            + "{\"name\":\"李四\",\"age\":11,\"address\":\"武汉\"},"
                            + "{\"name\":\"王五\",\"age\":31,\"address\":\"北京\"}]";
                JavaType javaType1 = objectMapper.getTypeFactory().constructParametricType(ArrayList.class, User.class);
                List<User> userList = (List<User>)objectMapper.readValue(listJson, javaType1);
                for (User user1 : userList) {
                    System.out.println(user1.getName()+"\t"+user1.getAge()+"\t"+user1.getAddress());
                }
                
                //JSON转map
                String mapJson = "{\"one\":{\"name\":\"张三\",\"age\":21,\"address\":\"深圳\"},"
                        + "\"two\":{\"name\":\"李四\",\"age\":11,\"address\":\"武汉\"},"
                        + "\"three\":{\"name\":\"王五\",\"age\":31,\"address\":\"北京\"}}";
                JavaType javaType2 = objectMapper.getTypeFactory().constructParametricType(HashMap.class, String.class, User.class);
                Map<String,User> userMap = (Map<String,User>)objectMapper.readValue(mapJson, javaType2);
                User one = userMap.get("one");
                User two = userMap.get("two");
                User three = userMap.get("three");
                System.out.println(one.getName()+"\t"+one.getAge()+"\t"+one.getAddress());
                System.out.println(two.getName()+"\t"+two.getAge()+"\t"+two.getAddress());
                System.out.println(three.getName()+"\t"+three.getAge()+"\t"+three.getAddress());
                
            } catch (IOException e) {
                e.printStackTrace();
            }
        }    
    }

![复制代码][copycode.gif]

四、测试jackson 1.x的使用方法：

![复制代码][copycode.gif]

package com.cn.jackson.test;
    
    import java.util.List;
    import java.util.Map;
    
    import org.codehaus.jackson.map.ObjectMapper;
    import org.codehaus.jackson.type.TypeReference;
    
    import com.cn.jackson.entity.User;
    
    public class Test_1_x {
    
        public static void main(String[] args) {
            try {
                //后面几种转换同Test_2_x一样  //对象转JSON  //map转JSON  //list转JSON  //JSON转java对象
                
                //JSON转list
                ObjectMapper objectMapper = new ObjectMapper();
                String listJson = "[{\"name\":\"张三\",\"age\":21,\"address\":\"深圳\"},"
                        + "{\"name\":\"李四\",\"age\":11,\"address\":\"武汉\"},"
                        + "{\"name\":\"王五\",\"age\":31,\"address\":\"北京\"}]";
                List<User> userList = objectMapper.readValue(listJson, new TypeReference<List<User>>() {});
                for (User user1 : userList) {
                    System.out.println(user1.getName()+"\t"+user1.getAge()+"\t"+user1.getAddress());
                }
                
                //JSON转map
                String mapJson = "{\"one\":{\"name\":\"张三\",\"age\":21,\"address\":\"深圳\"},"
                        + "\"two\":{\"name\":\"李四\",\"age\":11,\"address\":\"武汉\"},"
                        + "\"three\":{\"name\":\"王五\",\"age\":31,\"address\":\"北京\"}}";
                Map<String,User> userMap = objectMapper.readValue(mapJson, new TypeReference<Map<String,User>>() {});
                User one = userMap.get("one");
                User two = userMap.get("two");
                User three = userMap.get("three");
                System.out.println(one.getName()+"\t"+one.getAge()+"\t"+one.getAddress());
                System.out.println(two.getName()+"\t"+two.getAge()+"\t"+two.getAddress());
                System.out.println(three.getName()+"\t"+three.getAge()+"\t"+three.getAddress());
            } catch (Exception e) {
                // TODO: handle exception
            }
        }
    }

[ExpandedBlockStart.gif]: /images/20220528/b585033e4f924f509ea315d1299037c0.png
[copycode.gif]: /images/20220528/e6456b79c13e4741accb39fca0e4c2c2.png