【JSON】Jackson初学，及常用的例子

2022-09-12 14:28:52

现在很多公司的项目都基于SOA架构，系统间的调用有许多方式，其中一种常见的是用HTTP协议、以JSON格式返回结果。

这使得JSON的使用更加普遍。而市面上处理JSON的框架五花八门，常见的有JSONObject、GSON、Jackson等。

现在我们来学习Jackson，及记录常用的一些例子

版本说明

<dependencies>

    <dependency>

        <groupId>com.fasterxml.jackson.core</groupId>

        <artifactId>jackson-core</artifactId>

        <version>2.1.4</version>

    </dependency>

    <dependency>

        <groupId>com.fasterxml.jackson.core</groupId>

        <artifactId>jackson-databind</artifactId>

        <version>2.1.4</version>

    </dependency>

</dependencies>

最简单的例子

将Bean对象转换为JSON，在还原回来。（为了得到指定格式的日期格式，我指定了日期格式）

package com.nicchagil.demo.No001最简单的例子;

import java.io.IOException;

import java.sql.Timestamp;

import java.text.SimpleDateFormat;

import java.util.Calendar;

import org.junit.Test;

import com.fasterxml.jackson.core.JsonProcessingException;

import com.fasterxml.jackson.databind.ObjectMapper;

public class Call {

    @Test

    public void writeJson() throws JsonProcessingException {

        ObjectMapper objectMapper = new ObjectMapper();

        objectMapper.setDateFormat(new SimpleDateFormat("yyyy-MM-dd HH:mm:SS"));

        String json = objectMapper.writeValueAsString(new User(999, "Nick Huang", new Timestamp(Calendar.getInstance().getTimeInMillis())));

        System.out.println(json);

    }

    @Test

    public void readJson() throws IOException {

        String json = "{\"id\":999,\"name\":\"Nick Huang\",\"birthday\":\"2015-10-21 15:45:673\"}";

        ObjectMapper objectMapper = new ObjectMapper();

        objectMapper.setDateFormat(new SimpleDateFormat("yyyy-MM-dd HH:mm:SS"));

        User user = objectMapper.readValue(json, User.class);

        System.out.println(user);

    }

}

还需要一个Bean类型

package com.nicchagil.demo.No001最简单的例子;

import java.sql.Timestamp;

public class User {

    private Integer id;

    private String name;

    private Timestamp birthday;

    public Integer getId() {

        return id;

    }

    public void setId(Integer id) {

        this.id = id;

    }

    public String getName() {

        return name;

    }

    public void setName(String name) {

        this.name = name;

    }

    public Timestamp getBirthday() {

        return birthday;

    }

    public void setBirthday(Timestamp birthday) {

        this.birthday = birthday;

    }

    public User(Integer id, String name, Timestamp birthday) {

        super();

        this.id = id;

        this.name = name;

        this.birthday = birthday;

    }

    public User() {

        super();

    }

    @Override

    public String toString() {

        StringBuilder builder = new StringBuilder();

        builder.append("User [id=").append(id).append(", name=").append(name)

                .append(", birthday=").append(birthday).append("]");

        return builder.toString();

    }

}

日志如下

{"id":999,"name":"Nick Huang","birthday":"2015-10-22 17:34:318"}

User [id=999, name=Nick Huang, birthday=2015-10-21 15:45:00.673]

有泛型、集合的情况，如何指定转换的结构

package com.nicchagil.demo.No002含泛型和集合;

import java.io.IOException;

import java.sql.Timestamp;

import java.util.Calendar;

import java.util.HashMap;

import java.util.Map;

import org.junit.Test;

import com.fasterxml.jackson.core.JsonProcessingException;

import com.fasterxml.jackson.core.type.TypeReference;

import com.fasterxml.jackson.databind.ObjectMapper;

public class Call {

    @Test

    public void writeJson() throws JsonProcessingException {

        ObjectMapper objectMapper = new ObjectMapper();

        Map<String, Object> map = new HashMap<String, Object>();

        map.put("Nick", new User(999, "Nick Huang", new Timestamp(Calendar.getInstance().getTimeInMillis())));

        map.put("Robbin", new User(998, "Robbin", new Timestamp(Calendar.getInstance().getTimeInMillis())));

        String json = objectMapper.writeValueAsString(map);

        System.out.println(json);

    }

    @Test

    public void readJson() throws IOException {

        String json = "{\"Robbin\":{\"id\":998,\"name\":\"Robbin\",\"birthday\":1445415635096},\"Nick\":{\"id\":999,\"name\":\"Nick Huang\",\"birthday\":1445415635096}}";

        ObjectMapper objectMapper = new ObjectMapper();

        Map<String, User> map = objectMapper.readValue(json, new TypeReference<Map<String, User>>() {});

        System.out.println(map);

    }

}

日志如下

{"Robbin":{"id":998,"name":"Robbin","birthday":1445506610097},"Nick":{"id":999,"name":"Nick Huang","birthday":1445506610097}}

{Robbin=User [id=998, name=Robbin, birthday=2015-10-21 16:20:35.096], Nick=User [id=999, name=Nick Huang, birthday=2015-10-21 16:20:35.096]}

更复杂的结构呢

比如Map里面的不同key值对应的类型不同（我这个只是土方法，有好方法的童靴提示下哦）(>_<)

package com.nicchagil.demo.No003复杂结构;

import java.io.IOException;

import java.sql.Timestamp;

import java.util.Calendar;

import java.util.HashMap;

import java.util.Map;

import org.junit.Test;

import com.fasterxml.jackson.core.JsonProcessingException;

import com.fasterxml.jackson.databind.ObjectMapper;

import com.nicchagil.demo.No001最简单的例子.User;

public class Call {

    @Test

    public void writeJson() throws JsonProcessingException {

        ObjectMapper objectMapper = new ObjectMapper();

        Map<String, Object> map = new HashMap<String, Object>();

        map.put("code", "success");

        map.put("data", new User(999, "Nick Huang", new Timestamp(Calendar.getInstance().getTimeInMillis())));

        String json = objectMapper.writeValueAsString(map);

        System.out.println(json);

    }

    @Test

    public void readJson() throws IOException {

        String json = "{\"data\":{\"id\":999,\"name\":\"Nick Huang\",\"birthday\":1445502596155},\"code\":\"success\"}";

        ObjectMapper objectMapper = new ObjectMapper();

        Map<String, Object> map = objectMapper.readValue(json, Map.class);

        Object data = map.get("data");

        User user = objectMapper.convertValue(data, User.class);

        map.put("data", user);

        System.out.println(map);

        /* 打印出类型 */

        System.out.println("code's type : " + map.get("code").getClass().toString());

        System.out.println("data's type : " + map.get("data").getClass().toString());

    }

}

日志如下

{"data":{"id":999,"name":"Nick Huang","birthday":1445506936594},"code":"success"}

{data=User [id=999, name=Nick Huang, birthday=2015-10-22 16:29:56.155], code=success}

code's type : class java.lang.String

data's type : class com.nicchagil.demo.No001最简单的例子.User

简单的工具类

import java.io.IOException;

import java.sql.Timestamp;

import java.text.SimpleDateFormat;

import java.util.Calendar;

import java.util.Date;

import java.util.HashMap;

import java.util.Map;

import org.junit.Test;

import com.fasterxml.jackson.core.JsonProcessingException;

import com.fasterxml.jackson.core.type.TypeReference;

import com.fasterxml.jackson.databind.ObjectMapper;

public class JSONUtil {

    /* 公共的ObjectMapper */

    private static ObjectMapper commonObjectMapper = new ObjectMapper();

    static {

        commonObjectMapper.setDateFormat(new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"));

    }

    /**

     * 转JSON

     */

    public static String toJSON(Object obj) {

        String json = null;

        try {

            json = commonObjectMapper.writeValueAsString(obj);

        } catch (JsonProcessingException e) {

            throw new RuntimeException("Bean->JSON转换失败");

        }

        return json;

    }

    /**

     * 转Bean

     */

    public static <T> T toBean(String json, TypeReference<T> valueTypeRef) {

        T t = null;

        try {

            t = commonObjectMapper.readValue(json, valueTypeRef);

        } catch (IOException e) {

            throw new RuntimeException("JSON->Bean转换失败");

        }

        return t;

    }

    @Test

    public void toJSONTest() {

        Map<String, Object> map = new HashMap<String, Object>();

        map.put("id", "123");

        map.put("name", "Nick Huang");

        map.put("createTime", new Date());

        map.put("updateTime", new Timestamp(new Date().getTime()));

        map.put("sendTime", Calendar.getInstance());

        System.out.println(JSONUtil.toJSON(map));

    }

    @Test

    public void toBeanTest() {

        System.out.println(JSONUtil.toBean("{\"createTime\":\"2017-07-26 10:09:58\",\"name\":\"Nick Huang\",\"updateTime\":\"2017-07-26 10:09:58\",\"id\":\"123\",\"sendTime\":\"2017-07-26 10:09:58\"}",

                new TypeReference<Map<String, Object>>() {}));

    }

}
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