java集合详解（入门篇）

JSON

JSON & JavaScript对象相互转换

JavaScript对象 ——> JSON对象

<script type="text/javascript">
    
        //编写一个JavaScript对象
        var user = {
            name: "wei_shuo",
            age: 18,
            sex: "男"
        };

        //将JavaScript对象转换为JSON对象
        let json = JSON.stringify(user);
        console.log(json);

    </script>

JSON对象 ——> JavaScript对象

    <script type="text/javascript">
        //编写一个JavaScript对象
        var user = {
            name: "wei_shuo",
            age: 18,
            sex: "男"
        };

        //将JSON对象对象转换为JavaScript对象
        let obj = JSON.parse(json);
        console.log(obj)
        
    </script>

var、let、const | 全局、函数、块级作用域

Jackson

环境搭建

JSON乱码解决

注解方式

    //produces = "application/json;charset=utf-8" : 解决JSON对象乱码问题
    @RequestMapping(value = "/j1",produces = "application/json;charset=utf-8")

Spring配置方式

  <!--JSON乱码解决-->
    <mvc:annotation-driven>
        <mvc:message-converters register-defaults="true">
            <bean class="org.springframework.http.converter.StringHttpMessageConverter">
                <constructor-arg value="UTF-8"/>
            </bean>
            <bean class="org.springframework.http.converter.json.MappingJackson2HttpMessageConverter">
                <property name="objectMapper">
                    <bean class="org.springframework.http.converter.json.Jackson2ObjectMapperFactoryBean">
                        <property name="failOnEmptyBeans" value="false"/>
                    </bean>
                </property>
            </bean>
        </mvc:message-converters>
    </mvc:annotation-driven>

返回JSON对象

FastJson

环境搭建

Java <——> Json相互转换

@RestController
public class UserController {
    
    @RequestMapping("/j1")
    public String json1() throws JsonProcessingException {

        //创建集合对象
        ArrayList<User> userList = new ArrayList<>();
        //创建对象
        User user1 = new User("wei_shuo", 18, "男");
        User user2 = new User("tian_tain", 19, "男");
        User user3 = new User("wu_wu", 14, "男");
        User user4 = new User("qi_qi", 25, "男");
        userList.add(user1);
        userList.add(user2);
        userList.add(user3);
        userList.add(user4);

        System.out.println("Java对象——>Json字符串");
        String str1 = JSON.toJSONString(userList);
        System.out.println("JSON字符串：" + str1);

        System.out.println("=================");
        String str2 = JSON.toJSONString(user1);
        System.out.println("JSON字符串：" + str2);
        System.out.println("=================");

        System.out.println("Json字符串——>Java对象");
        User Json_TO_Java1 = JSON.parseObject(str2, User.class);
        System.out.println("Java对象：" + Json_TO_Java1);

        System.out.println("Java对象——>Json对象");
        JSONObject jsonObject = (JSONObject) JSON.toJSON(user1);
        System.out.println("Json对象：" + jsonObject.getString("name"));

        System.out.println("Json对象——>Java对象");
        User Json_TO_Java2 = JSON.toJavaObject(jsonObject, User.class);
        System.out.println("Java对象：" + Json_TO_Java2);

        return "Hello";

    }
}

/*
输出结果：
Java对象——>Json字符串
JSON字符串：[{"age":18,"name":"wei_shuo","sex":"男"},{"age":19,"name":"tian_tain","sex":"男"},{"age":14,"name":"wu_wu","sex":"男"},{"age":25,"name":"qi_qi","sex":"男"}]
=================
JSON字符串：{"age":18,"name":"wei_shuo","sex":"男"}
=================
Json字符串——>Java对象
Java对象：User(name=wei_shuo, age=18, sex=男)
Java对象——>Json对象
Json对象：wei_shuo
Json对象——>Java对象
Java对象：User(name=wei_shuo, age=18, sex=男)
*/