jackson 学习笔记

Jackson以优异的解析性能赢得了好评，今天就看看Jackson的一些简单的用法。

Jackson使用之前先要下载，这里一共有三个jar包，想要获得完美的Jackson体验，这三个jar包都不可或缺。

Java–>json

1.将一个类以json字符串的形式输出：

    //将一个类以json字符串的形式输出
    @Test
    public void test1(){
        ObjectMapper mapper = new ObjectMapper();
        User user = new User();
        user.setMoney(1000);
        user.setUsername("张三");
        user.setPassword("123");
        try {
            System.out.println(mapper.writeValueAsString(user));
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

User.java

import java.io.Serializable;

public class User implements Serializable{

    private String username;
    private String password;

    //添加了transient属性的字段不会被存储
    private int money;

    public int getMoney() {
        return money;
    }
    public void setMoney(int money) {
        this.money = money;
    }
    public User() {
    }
    public User(String username, String password, int money) {
        this.username = username;
        this.password = password;
        this.money = money;
    }
    public String getUsername() {
        return username;
    }
    public void setUsername(String username) {
        this.username = username;
    }
    public String getPassword() {
        return password;
    }
    public void setPassword(String password) {
        this.password = password;
    }

输出：

2.以json字符串的形式输出一个稍微复杂的类：

Book.java

public class Book {

    private int id;
    private String name;
    private int price;
    private String author;
    private Detail detail;
    private Attribute attribute;

    public Attribute getAttribute() {
        return attribute;
    }
    public void setAttribute(Attribute attribute) {
        this.attribute = attribute;
    }
    public Detail getDetail() {
        return detail;
    }
    public void setDetail(Detail detail) {
        this.detail = detail;
    }
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public int getPrice() {
        return price;
    }
    public void setPrice(int price) {
        this.price = price;
    }
    public String getAuthor() {
        return author;
    }
    public void setAuthor(String author) {
        this.author = author;
    }
}

Detail.java

public class Detail {

    private String pressTime;
    private String storyTime;
    public String getPressTime() {
        return pressTime;
    }
    public void setPressTime(String pressTime) {
        this.pressTime = pressTime;
    }
    public String getStoryTime() {
        return storyTime;
    }
    public void setStoryTime(String storyTime) {
        this.storyTime = storyTime;
    }
}

Attribute.java

public class Attribute {

    private String category;
    private String edition;
    public String getCategory() {
        return category;
    }
    public void setCategory(String category) {
        this.category = category;
    }
    public String getEdition() {
        return edition;
    }
    public void setEdition(String edition) {
        this.edition = edition;
    }

}

输出为：

{"id":1,"name":"三国演义","price":20,"author":"罗贯中","detail":{"pressTime":"2001-01-01","storyTime":"196-05-06"},"attribute":{"category":"小说","edition":"9"}}

3.以json字符串输出一个List集合：

    @Test
    public void test2(){
        ObjectMapper mapper = new ObjectMapper();
        List<User> list = new ArrayList<User>();
        User u = new User("张三", "123", 1000);
        list.add(u);
        u = new User("李四", "456", 2000);
        list.add(u);
        u = new User("王五", "789", 3000);
        list.add(u);
        u = new User("赵六", "555", 4000);
        list.add(u);
        try {
            System.out.println(mapper.writeValueAsString(list));
        } catch (JsonProcessingException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

输出结果：

[{"username":"张三","password":"123","money":1000},{"username":"李四","password":"456","money":2000},{"username":"王五","password":"789","money":3000},{"username":"赵六","password":"555","money":4000}]

4.将一个Map以json字符串的形式输出：

    @Test
    public void test3(){
        ObjectMapper mapper = new ObjectMapper();
        Map<String, String> map = new HashMap<String, String>();
        map.put("username", "张三");
        map.put("password", "123456");
        try {
            System.out.println(mapper.writeValueAsString(map));
        } catch (JsonProcessingException e) {
            e.printStackTrace();
        }
    }

结果为：

5.如果想把List集合中的map以json字符串格式输出，又该如何？和前文List一样。

    @Test
    public void test4(){
        ObjectMapper mapper = new ObjectMapper();
        List<Map<String, String>> list = new ArrayList<Map<String,String>>();
        Map<String, String> map = new HashMap<String, String>();
        map.put("username", "张三");
        map.put("password", "123456");
        list.add(map);
        map = new HashMap<String, String>();
        map.put("username", "李四");
        map.put("password", "888888");
        list.add(map);
        try {
            System.out.println(mapper.writeValueAsString(list));
        } catch (JsonProcessingException e) {
            e.printStackTrace();
        }
    }

6.在看看一个Map中有Book.java,Book.java中又有其他类：

    @Test
    public void test1(){
        ObjectMapper mapper = new ObjectMapper();
        Detail detail = new Detail();
        detail.setPressTime("2001-01-01");
        detail.setStoryTime("196-05-06");
        Attribute attr = new Attribute();
        attr.setCategory("小说");
        attr.setEdition("9");
        Book book = new Book();
        book.setAttribute(attr);
        book.setAuthor("罗贯中");
        book.setDetail(detail);
        book.setId(1);
        book.setName("三国演义");
        book.setPrice(20);
        Map<String, Object> map = new HashMap<String, Object>();
        map.put("namespace", "books");
        map.put("book", book);
        try {
            System.out.println(mapper.writeValueAsString(map));
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

输出结果：

{"book":{"id":1,"name":"三国演义","price":20,"author":"罗贯中","detail":{"pressTime":"2001-01-01","storyTime":"196-05-06"},"attribute":{"category":"小说","edition":"9"}},"namespace":"books"}

Json–>java

1.json字符串转为javaBean：

javaBean hljs tex">    @Test
    public void test5(){
        String str = "{\"id\":1,\"name\":\"三国演义\",\"price\":20,\"author\":\"罗贯中\",\"detail\":{\"pressTime\":\"2001-01-01\",\"storyTime\":\"196-05-06\"},\"attribute\":{\"category\":\"小说\",\"edition\":\"9\"}}";
        ObjectMapper mapper = new ObjectMapper();
        try {
            Book book = mapper.readValue(str, Book.class);
            System.out.println(book.getAuthor()+","+book.getAttribute().getCategory());
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

2.json字符串转为List

    //json-->List
    @Test
    public void test6(){
        String str = "[{\"username\":\"张三\",\"password\":\"123\",\"money\":1000},{\"username\":\"李四\",\"password\":\"456\",\"money\":2000},{\"username\":\"王五\",\"password\":\"789\",\"money\":3000},{\"username\":\"赵六\",\"password\":\"555\",\"money\":4000}]";
        ObjectMapper mapper = new ObjectMapper();
        try {
            List<User> us = mapper.readValue(str, new TypeReference<ArrayList<User>>() {});
            for (User user : us) {
                System.out.println(user.getUsername()+","+user.getMoney());
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

3.json字符串转为Map：

    //json-->map
    @Test
    public void test7(){
        String str = "{\"password\":\"888888\",\"username\":\"李四\"}";
        ObjectMapper mapper = new ObjectMapper();
        try {
            Map<String, String> map = mapper.readValue(str, new TypeReference<Map<String, String>>() {});
            for (String key : map.keySet()) {
                System.out.println(key+","+map.get(key));
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

唉，仔细一琢磨，这个Jackson真的好简单，以前一直以为好难，想起来小学的课文《小马过河》，看来还是要多实践。