首先需要引入fastjson的依赖文件，以下是maven的依赖：

然后是将json字符串写到文件中去：

import com.alibaba.fastjson.JSON;
import com.alibaba.fastjson.serializer.SerializerFeature;import java.io.File;
import java.io.FileOutputStream;
import java.io.OutputStreamWriter;
import java.io.Writer;
import java.nio.charset.StandardCharsets;public class JsonUtils {private static final String DEFAULT_SAVE_DIRECTORY = "upload/file/";private static String SEPARATOR = File.separator;private static SimpleDateFormat DateSdf = new SimpleDateFormat("yyyyMMdd");public static void saveJson(JSONObject data,Long taskId,Long cmdId) {//写入操作String content = JSON.toJSONString(data, SerializerFeature.PrettyFormat, SerializerFeature.WriteMapNullValue,SerializerFeature.WriteDateUseDateFormat);String filePath =DEFAULT_SAVE_DIRECTORY+ getStrDate() +"/"+ "taskId-"+taskId+"cmdId-"+cmdId+".txt";try {File file = new File(filePath);// 创建上级目录if (!file.getParentFile().exists()) {file.getParentFile().mkdirs();}// 如果文件存在，则删除文件if (file.exists()) {file.delete();}// 创建文件file.createNewFile();// 写入文件Writer write = new OutputStreamWriter(new FileOutputStream(file), StandardCharsets.UTF_8);write.write(content);write.flush();write.close();} catch (Exception e) {e.printStackTrace();}}private static String getStrDate() {return DateSdf.format(new Date());}
}