例子解析以下JSON数据

 {"code":0,
   "msg":"成功",
   "data":            
 [{
"host":"1068222.com",
"port":"",
"m_token":"490e20e70e7de5f21a24b14c12a393f6",
"category":"sd",
"sub_category":"M1049",
"flyback_date":"2025-02-17",
"versions":["0.4.2"],
"req_times":["2025-02-15 02:58:20"],
"create_time":"2025-02-18 06:58:20",
"update_time":"2025-02-18 06:58:20"}]
}

以下以 Gson 库为例，展示如何解析这段 JSON 数据：

首先，需要在项目中引入 Gson 库的依赖。如果使用 Maven 项目，可以在pom.xml文件中添加以下依赖：

<dependency>
    <groupId>com.google.code.gson</groupId>
    <artifactId>gson</artifactId>
    <version>2.8.9</version>
</dependency>

 接下来，定义对应的 Java 类来映射 JSON 数据结构：

import java.util.List;

public class ResponseData {
    private int code;
    private String msg;
    private List<DataItem> data;

    public int getCode() {
        return code;
    }

    public void setCode(int code) {
        this.code = code;
    }

    public String getMsg() {
        return msg;
    }

    public void setMsg(String msg) {
        this.msg = msg;
    }

    public List<DataItem> getData() {
        return data;
    }

    public void setData(List<DataItem> data) {
        this.data = data;
    }

    public static class DataItem {
        private String host;
        private String port;
        private String m_token;
        private String category;
        private String sub_category;
        private String flyback_date;
        private List<String> versions;
        private List<String> req_times;
        private String create_time;
        private String update_time;

        public String getHost() {
            return host;
        }

        public void setHost(String host) {
            this.host = host;
        }

        public String getPort() {
            return port;
        }

        public void setPort(String port) {
            this.port = port;
        }

        public String getM_token() {
            return m_token;
        }

        public void setM_token(String m_token) {
            this.m_token = m_token;
        }

        public String getCategory() {
            return category;
        }

        public void setCategory(String category) {
            this.category = category;
        }

        public String getSub_category() {
            return sub_category;
        }

        public void setSub_category(String sub_category) {
            this.sub_category = sub_category;
        }

        public String getFlyback_date() {
            return flyback_date;
        }

        public void setFlyback_date(String flyback_date) {
            this.flyback_date = flyback_date;
        }

        public List<String> getVersions() {
            return versions;
        }

        public void setVersions(List<String> versions) {
            this.versions = versions;
        }

        public List<String> getReq_times() {
            return req_times;
        }

        public void setReq_times(List<String> req_times) {
            this.req_times = req_times;
        }

        public String getCreate_time() {
            return create_time;
        }

        public void setCreate_time(String create_time) {
            this.create_time = create_time;
        }

        public String getUpdate_time() {
            return update_time;
        }

        public void setUpdate_time(String update_time) {
            this.update_time = update_time;
        }
    }
}

然后，使用 Gson 库解析 JSON 数据：

import com.google.gson.Gson;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.List;

class ResponseData {
    private int code;
    private String msg;
    private List<DataItem> data;

    public int getCode() {
        return code;
    }

    public void setCode(int code) {
        this.code = code;
    }

    public String getMsg() {
        return msg;
    }

    public void setMsg(String msg) {
        this.msg = msg;
    }

    public List<DataItem> getData() {
        return data;
    }

    public void setData(List<DataItem> data) {
        this.data = data;
    }

    static class DataItem {
        private String host;
        private String port;
        private String m_token;
        private String category;
        private String sub_category;
        private String flyback_date;
        private List<String> versions;
        private List<String> req_times;
        private String create_time;
        private String update_time;

        public String getHost() {
            return host;
        }

        public void setHost(String host) {
            this.host = host;
        }

        public String getPort() {
            return port;
        }

        public void setPort(String port) {
            this.port = port;
        }

        public String getM_token() {
            return m_token;
        }

        public void setM_token(String m_token) {
            this.m_token = m_token;
        }

        public String getCategory() {
            return category;
        }

        public void setCategory(String category) {
            this.category = category;
        }

        public String getSub_category() {
            return sub_category;
        }

        public void setSub_category(String sub_category) {
            this.sub_category = sub_category;
        }

        public String getFlyback_date() {
            return flyback_date;
        }

        public void setFlyback_date(String flyback_date) {
            this.flyback_date = flyback_date;
        }

        public List<String> getVersions() {
            return versions;
        }

        public void setVersions(List<String> versions) {
            this.versions = versions;
        }

        public List<String> getReq_times() {
            return req_times;
        }

        public void setReq_times(List<String> req_times) {
            this.req_times = req_times;
        }

        public String getCreate_time() {
            return create_time;
        }

        public void setCreate_time(String create_time) {
            this.create_time = create_time;
        }

        public String getUpdate_time() {
            return update_time;
        }

        public void setUpdate_time(String update_time) {
            this.update_time = update_time;
        }
    }
}

public class JsonParsingExample {
    public static void main(String[] args) {
        String json = "{\"code\":0,\"msg\":\"成功\",\"data\":[{\"host\":\"1068222.com\",\"port\":\"\",\"m_token\":\"490e20e70e7de5f21a24b14c12a393f6\",\"category\":\"sd\",\"sub_category\":\"M1049\",\"flyback_date\":\"2025-02-17\",\"versions\":[\"0.4.2\"],\"req_times\":[\"2025-02-15 02:58:20\"],\"create_time\":\"2025-02-18 06:58:20\",\"update_time\":\"2025-02-18 06:58:20\"}]}";

        Gson gson = new Gson();
        ResponseData response = gson.fromJson(json, ResponseData.class);

        System.out.println("Code: " + response.getCode());
        System.out.println("Message: " + response.getMsg());

        for (ResponseData.DataItem item : response.getData()) {
            System.out.println("Host: " + item.getHost());
            System.out.println("Port: " + item.getPort());
            System.out.println("m_token: " + item.getM_token());
            System.out.println("Category: " + item.getCategory());
            System.out.println("Sub Category: " + item.getSub_category());
            System.out.println("Flyback Date: " + item.getFlyback_date());
            System.out.println("Versions: " + item.getVersions());
            System.out.println("Req Times: " + item.getReq_times());
            System.out.println("Create Time: " + item.getCreate_time());
            System.out.println("Update Time: " + item.getUpdate_time());

            if (!item.getReq_times().isEmpty()) {
                String firstReqTime = item.getReq_times().get(0);
                try {
                    SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
                    Date date = sdf.parse(firstReqTime);
                    long timestamp = date.getTime();
                    System.out.println("First Req Time Timestamp: " + timestamp);
                } catch (ParseException e) {
                    System.err.println("Failed to parse date: " + firstReqTime);
                    e.printStackTrace();
                }
            }
        }
    }
}

以上代码首先定义了与 JSON 数据结构对应的 Java 类，然后使用 Gson 库将 JSON 字符串解析为 Java 对象，并打印出解析后的数据。如果使用 Jackson 库，解析过程会有所不同，但原理类似。

将解析出的 req_times 列表中的第一个时间字符串转换为时间戳。在 Java 中，可以使用 SimpleDateFormat 类来解析日期时间字符串，并将其转换为 Date 对象，然后通过 Date 对象的 getTime() 方法获取对应的时间戳。

代码说明：

1. 日期格式化：使用 SimpleDateFormat 类，其构造函数传入 "yyyy-MM-dd HH:mm:ss" 作为日期时间的格式模板，该模板与 JSON 数据中的日期时间字符串格式相匹配。
2. 解析日期字符串：调用 SimpleDateFormat 对象的 parse() 方法将日期时间字符串解析为 Date 对象。
3. 获取时间戳：通过 Date 对象的 getTime() 方法获取对应的时间戳（从 1970 年 1 月 1 日 00:00:00 UTC 到该日期的毫秒数）。
4. 异常处理：使用 try-catch 块捕获 ParseException 异常，当日期时间字符串格式不符合模板时，会抛出该异常，捕获后打印错误信息并输出堆栈跟踪。

运行上述代码，在输出 Req Times 信息后，会额外输出第一个请求时间对应的时间戳。