Jackson 2开发详解

作者：chszs，转载需注明。博客主页：http://blog.csdn.net/chszs

Jackson 2库是流行的Java JSON解析库之一。本文主要讲述Jackson 2库的基本用法。

1、Jackson 2库

目前Jackson 2库的最新版本为2.6.3版。使用它需要以下依赖包。

    <dependency>
        <groupId>com.fasterxml.jackson.core</groupId>
        <artifactId>jackson-core</artifactId>
        <version>2.6.3</version>
    </dependency>
    <dependency>
        <groupId>com.fasterxml.jackson.core</groupId>
        <artifactId>jackson-databind</artifactId>
        <version>2.6.3</version>
    </dependency>
    <dependency>
        <groupId>com.fasterxml.jackson.core</groupId>
        <artifactId>jackson-annotations</artifactId>
        <version>2.6.3</version>
    </dependency>

基本的Java对象User.java

package json.ch.test;
public class User {
    private String name;
    private int year;
    private String describe;

    public User() {
        super();
    }

    public User(String name, int year, String describe) {
        super();
        this.name = name;
        this.year = year;
        this.describe = describe;
    }

    public String getName() {
        return name;
    }

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

    public int getYear() {
        return year;
    }

    public void setYear(int year) {
        this.year = year;
    }

    public String getDescribe() {
        return describe;
    }

    public void setDescribe(String describe) {
        this.describe = describe;
    }

    @Override
    public String toString() {
        return "User [name=" + name + ", year=" + year + ", describe=" + describe + "]";
    }
}

2、Java对象转换为JSON

使用writeValue(…)方法

    ObjectMapper mapper = new ObjectMapper();
    User user = new User("Zhang san", 20, "He is a young boy.");
    try {
        mapper.writeValue(new File("t1.json"), user);
    } catch (IOException e) {
        e.printStackTrace();
    }
    try {
        String jsonString = mapper.writeValueAsString(user);
        System.out.println(jsonString);
    } catch (JsonProcessingException e) {
        e.printStackTrace();
    }

3、JSON字符串转换为Java对象

使用readValue(…)方法

    ObjectMapper mapper = new ObjectMapper();
    String jsonString = "{\"name\":\"Zhang san\",\"year\":20,\"describe\":\"He is a young boy.\"}";
    User user;
    try {
        user = mapper.readValue(jsonString, User.class);
        System.out.println(user.toString());
    } catch (IOException e) {
        e.printStackTrace();
    }
    try {
        User user1 = mapper.readValue(new File("t1.json"), User.class);
        System.out.println(user1.toString());
    } catch (IOException e) {
        e.printStackTrace();
    }

4、@JsonView注释

@JsonView注释是一个非常有用的注释，它用于控制对象中的字段。

重写User.java

package json.ch.test;

import com.fasterxml.jackson.annotation.JsonView;
public class User {
    @JsonView(Views.Normal.class)
    private String name;
    @JsonView(Views.Normal.class)
    private int year;
    @JsonView(Views.Manager.class)
    private String describe;

    public User() {
        super();
    }

    public User(String name, int year, String describe) {
        super();
        this.name = name;
        this.year = year;
        this.describe = describe;
    }

    public String getName() {
        return name;
    }

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

    public int getYear() {
        return year;
    }

    public void setYear(int year) {
        this.year = year;
    }

    public String getDescribe() {
        return describe;
    }

    public void setDescribe(String describe) {
        this.describe = describe;
    }

    @Override
    public String toString() {
        return "User [name=" + name + ", year=" + year + ", describe=" + describe + "]";
    }
}

定义Views.java

package json.ch.test;
public class Views {
    public static class Normal{};
    public static class Manager extends Normal{};
}

测试代码:

package json.ch.test;

import com.fasterxml.jackson.databind.ObjectMapper;

public class Test3 {
    public static void main(String[] args) {
        ObjectMapper mapper = new ObjectMapper();
        User user = new User("Zhang san", 20, "He is a young boy.");
        try{
            System.out.println("Normal View");
            String normalView = mapper.writerWithView(Views.Normal.class)
                    .writeValueAsString(user);
            System.out.println(normalView);
            String json1 = "{\"name\":\"Zhang san\",\"year\":20}";
            User normalUser = mapper.readerWithView(Views.Normal.class)
                    .forType(User.class).readValue(json1);
            System.out.println(normalUser);
            System.out.println("Manager View");
            String managerView = mapper.writerWithView(Views.Manager.class)
                    .writeValueAsString(user);
            System.out.println(managerView);
            String json2 = "{\"name\":\"Zhang san\",\"year\":20,\"describe\":\"He is a young boy.\"}";
            User managerUser = mapper.readerWithView(Views.Manager.class)
                    .forType(User.class).readValue(json2);
            System.out.println(managerUser.toString());
        }catch(Exception e){
            e.printStackTrace();
        }
    }
}

输出结果：

Normal View
{"name":"Zhang san","year":20}
User [name=Zhang san, year=20, describe=null]
Manager View
{"name":"Zhang san","year":20,"describe":"He is a young boy."}
User [name=Zhang san, year=20, describe=He is a young boy.]