gson介绍

Google Gson是一个简单的基于Java的库，用于将Java对象序列化为JSON，反之亦然。 它是由Google开发的一个开源库。
以下几点说明为什么应该使用这个库 :
标准化 - Gson是一个由Google管理的标准化库。
高效 - 这是对Java标准库的可靠，快速和高效的扩展。
优化 - Gson库经过高度优化。
支持泛型 - 它为泛型提供了广泛的支持。
支持复杂的内部类 - 它支持具有深度继承层次结构的复杂对象。

gson引入

maven引入

<dependency>
  <groupId>com.google.code.gson</groupId>
  <artifactId>gson</artifactId>
  <version>2.8.2</version>
</dependency>

gson的api快速入门

//javaBean-->json
    @Test
    public void test1(){
    
        Gson gson = new Gson();
        Person p = new Person("张三", "123", 500, new Book("三国演义", "罗贯中"));
        String json = gson.toJson(p);
        System.out.println(json);
    }
//json-->javaBean
    @Test
    public void test2(){
    
        String json = "{\"username\":\"张三\",\"password\":\"123\",\"money\":500,\"book\":{\"id\":0,\"name\":\"三国演义\",\"price\":0,\"author\":\"罗贯中\"}}";
        Gson gson = new Gson();
        Person p = gson.fromJson(json, Person.class);
        System.out.println(p.getUsername()+"--"+p.getBook().getName());
    }
//list-->json
    @Test
    public void test3() {
    
        List<Person> list = new ArrayList<Person>();
        Person p = new Person("张三", "123", 500, new Book("三国演义", "罗贯中"));
        list.add(p);
        p = new Person("李四", "123", 500, new Book("三国演义", "罗贯中"));
        list.add(p);
        Gson gson = new Gson();
        String gsonStr = gson.toJson(list);
        System.out.println(gsonStr);
    }
//map-->json
    @Test
    public void test4() {
    
        Map<String, Person> map = new HashMap<String, Person>();
        Person p = new Person("张三", "123", 500, new Book("三国演义", "罗贯中"));
        map.put("p1", p);
        p = new Person("李四", "123", 500, new Book("三国演义", "罗贯中"));
        map.put("p2", p);
        Gson gson = new Gson();
        String gsonStr = gson.toJson(map);
        System.out.println(gsonStr);
    }

//json-->list
    @Test
    public void test5() {
    
        String str = "[{\"username\":\"张三\",\"password\":\"123\",\"money\":500,\"book\":{\"id\":0,\"name\":\"三国演义\",\"price\":0,\"author\":\"罗贯中\"}},{\"username\":\"李四\",\"password\":\"123\",\"money\":500,\"book\":{\"id\":0,\"name\":\"三国演义\",\"price\":0,\"author\":\"罗贯中\"}}]";
        Gson gson = new Gson();
        List<Person> ps = gson.fromJson(str,new TypeToken<List<Person>>() {
      
        }.getType());
        for (Person person : ps) {
    
            System.out.println(person.getUsername()+"---"+person.getBook().getName());
        }

    }

//json-->map
    @Test
    public void test6(){
    
        String str = "{\"p1\":{\"username\":\"张三\",\"password\":\"123\",\"money\":500,\"book\":{\"id\":0,\"name\":\"三国演义\",\"price\":0,\"author\":\"罗贯中\"}},\"p2\":{\"username\":\"李四\",\"password\":\"123\",\"money\":500,\"book\":{\"id\":0,\"name\":\"红楼梦\",\"price\":0,\"author\":\"曹雪芹\"}}}";
        Gson gson = new Gson();
        Map<String, Person> map = gson.fromJson(str, new TypeToken<Map<String, Person>>(){
    }.getType());
        Set<String> keys = map.keySet();
        for(String key:keys){
    
            System.out.println(map.get(key).getUsername()+"--"+map.get(key).getBook().getName());
        }
    }

public class Person {
    

    private String username;
    private String password;
    private int money;
    private Book book;

    public Person() {
    
    }

    public Person(Book book) {
    
        this.book = book;
    }

    public Book getBook() {
    
        return book;
    }
    public void setBook(Book book) {
    
        this.book = book;
    }
    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;
    }
    public int getMoney() {
    
        return money;
    }
    public void setMoney(int money) {
    
        this.money = money;
    }

    public Person(String username, String password, int money, Book book) {
    
        super();
        this.username = username;
        this.password = password;
        this.money = money;
        this.book = book;
    }

}

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;
    }
    public Book(String name, String author) {
    
        this.name = name;
        this.author = author;
    }
    public Book() {
    
    }

}

注意事项：
把json字符串转为集合时，​​new TypeToken<>(){}.getType()​​在eclipse中貌似不能够自动提示，如果你的电脑也是这样的话，建议这里的代码自己手动敲一下，eclipse只是不会自动提示，自己敲出来的是不会报错的，嗯，我就遇到这一个小小的问题，总体来说这个东东还是很好用的。