提高java代码的效率

我编写了一些java代码来自动生成要导入MongoDB的JSON文件。 这是我的代码：

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.Random;

import org.apache.commons.lang3.RandomStringUtils;

public class Coach {

    public static void main(String[] args) throws IOException 
    {

        File f = new File("coach.json");

        if(f.exists()) 

        {
            FileOutputStream fos = new FileOutputStream("coach.json", true);
            PrintWriter pw = new PrintWriter(fos);
            pw.append(createString());
            System.out.println("The file \"Progettino.json\" already exists. New documents have been added at the bottom.");
            pw.flush();
            pw.close();
        }

        if(f.createNewFile())

        {
            PrintWriter pw = new PrintWriter(f);    
            pw.println(createString());
            System.out.println("The file \"Progettino.json\" was created. New documents added.");
            pw.flush();
            pw.close();
        }

    }

    public static String createString() 
    {
        Random random = new Random();

        String id = "{\n\"_id\":" + "\""; 

        String singleDocument="";

        for(int i=0; i<10001;i++) 
        {
            String name = "\"name\":" + "\"" + RandomStringUtils.randomAlphabetic(10) + "\",\n" ;
            String surname =   "\"surname\":" + "\"" + RandomStringUtils.randomAlphabetic(10) + "\",\n";    
            String age = "\"age\":" + "\"" + String.valueOf(random.nextInt(60)) + "\",\n ";
            String date_of_birth = "\"date_Of_birth\":" + "{\"day\":"  + String.valueOf(random.nextInt(31)) + "," +
                    "\"month\":"  + String.valueOf(random.nextInt(12)) + ", " + 
                    "\"year\":"  + String.valueOf(random.nextInt(1900)) + "},\n";
            String place_Of_birth = "\"place_Of_birth\":" + "\"" + RandomStringUtils.randomAlphabetic(10) + "\", \n";
            String nationality = "\"nationality\":" + "\"" + RandomStringUtils.randomAlphabetic(10) + "\", \n";
            String preferred_formation = "\"preferred_formation\":" + "\"" + RandomStringUtils.randomAlphabetic(10) + "\", \n";
            String coached_Team = "\"coached_Team\": [" + "{\"team_id\":\""  + RandomStringUtils.randomAlphabetic(3) + "." + RandomStringUtils.randomAlphabetic(3) + "\"," +
                    "\"in_charge\": { \"from\":{"  + "\"day\":"  + String.valueOf(random.nextInt(31)) + "," +
                    "\"month\":"  + String.valueOf(random.nextInt(12)) + ", " + 
                    "\"year\":"  + String.valueOf(random.nextInt(1900)) + "} }," + 
                    "\"matches\":"  + String.valueOf(random.nextInt(400)) + "},\n" + 
                    "{\"team_id\":\""  + RandomStringUtils.randomAlphabetic(3) + "." + RandomStringUtils.randomAlphabetic(3) + "\"," +
                    "\"in_charge\": { \"from\":{"  + "\"day\":"  + String.valueOf(random.nextInt(31)) + "," +
                    "\"month\":"  + String.valueOf(random.nextInt(12)) + ", " + 
                    "\"year\":"  + String.valueOf(random.nextInt(1900)) + "} }," + 
                    "\"matches\":"  + String.valueOf(random.nextInt(400)) + "}" +
                    "]\n}";


            singleDocument = singleDocument + id + String.valueOf(i) + "\", \n" + name + surname + age + date_of_birth +
                    place_Of_birth + nationality + preferred_formation + coached_Team;
        }

        return singleDocument;
    } 

}

---

我的问题是这个程序效率不高。例如，如果我想生成10万个文档，大约需要30分钟。是否有可能使该代码更有效

您正在以最慢的方式创建一个非常长的字符串：重复复制和连接

---

我可以告诉您使用

StringBuilder

累积长字符串，但是完全跳过创建字符串会获得更好的性能。将

PrintWriter

作为参数传递并直接写入

在我看来，这个问题更适合你。不管怎样，你为什么不使用现成的解决方案，比如Gson？对于您的代码，我想不起-使用

StringBuilder

，而不是连接数千个不可变的

String

s。非常感谢。我将PrintWriter作为参数传递，代码“仅”5秒钟就生成了100万个文档。

    {
    "_id":"30", 
    "name":"EDSDoIDENx",
    "surname":"ygbECUwPap",
    "age":"37",
     "date_Of_birth":{"day":6,"month":4, "year":827},
    "place_Of_birth":"HkGbFBaDIN", 
    "nationality":"yeEFVNmuvI", 
    "preferred_formation":"ITyvWidryK", 
    "coached_Team": [{"team_id":"ceV.iKu","in_charge": { "from":{"day":25,"month":7, "year":958} },"matches":103},
    {"team_id":"gQQ.fdq","in_charge": { "from":{"day":15,"month":9, "year":121} },"matches":387}]
    }
    {
    "_id":"31", 
    "name":"YoRYcdTjzk",
    "surname":"rbpyGHqLjY",
    "age":"43",
     "date_Of_birth":{"day":17,"month":2, "year":524},
    "place_Of_birth":"hWqooTGCHa", 
    "nationality":"eZDKzMelkt", 
    "preferred_formation":"vvrAhlJqji", 
    "coached_Team": [{"team_id":"TUI.HaY","in_charge": { "from":{"day":6,"month":0, "year":6} },"matches":182},
    {"team_id":"fMh.IBi","in_charge": { "from":{"day":30,"month":7, "year":747} },"matches":204}]
    }
    {
    "_id":"32", 
    "name":"DTAeGtWmrr",
    "surname":"lxtYGXmgCh",
    "age":"1",
     "date_Of_birth":{"day":2,"month":6, "year":1208},
    "place_Of_birth":"MtVqulnaQv", 
    "nationality":"iMrlbIpuCb", 
    "preferred_formation":"qkpcFdjXOz", 
    "coached_Team": [{"team_id":"FVo.ZWu","in_charge": { "from":{"day":14,"month":0, "year":937} },"matches":316},
    {"team_id":"yaX.iZH","in_charge": { "from":{"day":22,"month":4, "year":1620} },"matches":275}]
    }