修改并重写 json 文件中的密钥

Question

我目前在使用 java 中的 JSON 文件时遇到了一些问题。这里的目标是将 JSON 文件中的每个“timestamp_ms”修改为 UTC 时间和日期

我的代码输入 JSON 文件，读取它并在最后以我想要的 JSON 格式输出。然后我遍历所有 timestamp_ms 并转换它们。

我现在想用我得到的输出替换所有 timestamp_ms 并再次将文件重写为 JSON 格式（现在 timestamp_ms 已转换）。我漫游了 SO 答案，但到目前为止没有成功。任何人都可以知道实现此目标的好方法吗？

代码如下：

public class JsonMain {
    public static void main(String[] args) throws IOException {
        String first = "chatMessage.json";
        String jsonSource = new String((Files.readAllBytes(Paths.get(first))),"UTF-8");
        //print the json file
        System.out.println(jsonSource);

        JSONObject obj = new JSONObject(jsonSource);
        JSONArray arr = new JSONArray(obj.getJSONArray("messages"));

        //iterate trough all the timestamp_ms and get the value
        for(int i=0; i< arr.length(); i++)
        {
            long time = (long)arr.getJSONObject(i).get("timestamp_ms");
            SimpleDateFormat sdf = new SimpleDateFormat();
            sdf.setTimeZone(TimeZone.getTimeZone("UTC"));
            System.out.println(sdf.format(new Date(time)));
            //arr.put("timestamp_ms",sdf.format(new Date(time)));
        }

    }
}

这是 json 文件 chatMessage.json

{
  "participants": [
    {
      "name": "User1"
    },
    {
      "name": "User2"
    }
  ],
  "messages": [
    {
      "sender_name": "User1",
      "timestamp_ms": 1620663455808,
      "content": "Hello ç á à â ã ",
      "type": "Generic",
      "is_unsent": false
    },
    {
      "sender_name": "User2",
      "timestamp_ms": 1620663401347,
      "content": "Hi, how are you?",
      "type": "Generic",
      "is_unsent": false
    },
    {
      "sender_name": "User1",
      "timestamp_ms": 1620662999730,
      "content": "\u00c3\u0089 to utf?",
      "type": "Generic",
      "is_unsent": false
    }
  ],
  "title": "chatTitle",
  "is_still_participant": true,
  "thread_type": "RegularGroup",
  "thread_path": "inbox/chatTitle_4hyfdfnnhw"
}

Answer 1

你很接近。

只需要引用JSON消息对象而不是数组，然后重写文件。

你可以这样做：

String first = "chatMessage.json";
String jsonSource = new String((Files.readAllBytes(Paths.get(first))),"UTF-8");
//print the json file
System.out.println(jsonSource);

JSONObject obj = new JSONObject(jsonSource);
JSONArray arr = new JSONArray(obj.getJSONArray("messages"));

//iterate trough all the timestamp_ms and get the value
for(int i=0; i< arr.length(); i++) {
    JSONObject currMessage = arr.getJSONObject(i);
    long time = (long) currMessage.get("timestamp_ms");
    SimpleDateFormat sdf = new SimpleDateFormat();
    sdf.setTimeZone(TimeZone.getTimeZone("UTC"));
    System.out.println(sdf.format(new Date(time)));
    currMessage.put("timestamp_ms", sdf.format(new Date(time)));
}

Files.write(Paths.get(first), obj.toString(2).getBytes());

String output = new String((Files.readAllBytes(Paths.get(first))),"UTF-8");
System.out.println(output);

输出：

{
    "is_still_participant": true,
    "thread_type": "RegularGroup",
    "messages": [{
        "is_unsent": false,
        "sender_name": "User1",
        "timestamp_ms": "10.5.2021, 16:17",
        "type": "Generic",
        "content": "Hello ç á à â ã "
    }, {
        "is_unsent": false,
        "sender_name": "User2",
        "timestamp_ms": "10.5.2021, 16:16",
        "type": "Generic",
        "content": "Hi, how are you?"
    }, {
        "is_unsent": false,
        "sender_name": "User1",
        "timestamp_ms": "10.5.2021, 16:09",
        "type": "Generic",
        "content": "Ã\u0089 to utf?"
    }],
    "title": "chatTitle",
    "thread_path": "inbox/chatTitle_4hyfdfnnhw",
    "participants": [{
        "name": "User1"
    }, {
        "name": "User2"
    }]
}

Answer 2

我建议使用 token/event/stream-based 解决方案。下面只是使用tiny parser/generator lib https://github.com/anatolygudkov/green-jelly（Gson和Jackson都提供了面向流的API）的说明：

import org.green.jelly.AppendableWriter;
import org.green.jelly.CharArrayCharSequence;
import org.green.jelly.JsonEventPump;
import org.green.jelly.JsonNumber;
import org.green.jelly.JsonParser;

import java.io.FileReader;
import java.io.FileWriter;
import java.io.Writer;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.TimeZone;

public class TransformMyJson {
    public static void main(String[] args) throws Exception {
        try (FileReader input = new FileReader("/home/user/input.json");
                FileWriter output = new FileWriter("/home/user/output.json")) {

            final JsonParser parser = new JsonParser();
            parser.setListener(new MyTransformer(output));

            final CharArrayCharSequence charSequence = new CharArrayCharSequence(4096);
            final char[] buffer = charSequence.getChars();

            int len;
            while ((len = input.read(buffer,0, buffer.length)) > -1) {
                charSequence.setLength(len);
                parser.parse(charSequence);
            }
            parser.eoj();
        }
    }

    static class MyTransformer extends JsonEventPump {
        private final SimpleDateFormat sdf = new SimpleDateFormat();
        private boolean isTimestamp;

        MyTransformer(final Writer output) {
            super(new AppendableWriter<>(output));
            sdf.setTimeZone(TimeZone.getTimeZone("UTC"));
        }

        @Override
        public boolean onObjectMember(final CharSequence name) {
            isTimestamp = "timestamp_ms".contentEquals(name);
            return super.onObjectMember(name);
        }

        @Override
        public boolean onNumberValue(final JsonNumber number) {
            if (isTimestamp) {
                return super.onStringValue(sdf.format(new Date(number.mantissa())));
            }
            return super.onNumberValue(number);
        }
    }
}

此类解决方案的道具：

file/data不需要完全加载到内存中，您可以毫无问题地处理megs/gigs
它比任何对象映射代码工作得更快，尤其是对于大文件
您自然具有与结果相同的 JSON 结构
很容易实现任何自定义type/rule 转换

修改并重写 json 文件中的密钥

Modify and re-write key from json file

java

json

jackson