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.]