在java中将对象数组写入csv文件

Question

我正在尝试获取一个初始 CSV 文件，将其传递给一个类，该类检查另一个文件是否具有 A 或 D，然后添加或删除数组对象的关联条目。

pokemon.csv 示例：

1, Bulbasaur
2, Ivysaur
3, venasaur

changeList.csv 示例：

A, Charizard
A, Suirtle
D, 2

话虽如此，我在将新数组的内容转换为新的 CSV 文件时遇到了很多麻烦。我检查了我的数组和类文件是否正常工作。我一直在尝试将“pokedex1”对象数组的最终内容放入新的 CSV 文件中，但未能成功。

主文件

import java.io.File; 
import java.io.FileNotFoundException;
import java.io.FileWriter;
import java.io.IOException;
import java.util.Scanner;

public class PokedexManager {

public static void  printArray(String[] array) {
    System.out.print("Contents of array: ");

    for(int i = 0; i < array.length; i++) {
        if(i == array.length - 1) {
            System.out.print(array[i]);
        }else {
            System.out.print(array[i] + ",");
        }
    }
    System.out.println();
}

public static void main(String[] args) {
    try {
        //output for pokedex1 using PokemonNoGaps class
        PokemonNoGaps pokedex1 = new PokemonNoGaps();

        //initializes scanner to read from csv file
        String pokedexFilename = "pokedex.csv";
        File pokedexFile = new File(pokedexFilename);
        Scanner pokescanner = new Scanner(pokedexFile);

        //reads csv file, parses it into an array, and then adds         new pokemon objects to Pokemon class
        while(pokescanner.hasNextLine()) {
            String pokeLine = pokescanner.nextLine();
            String[] pokemonStringArray = pokeLine.split(", ");
            int id = Integer.parseInt(pokemonStringArray[0]);
            String name = pokemonStringArray[1];
            Pokemon apokemon = new Pokemon(id, name);
            pokedex1.add(apokemon);
        }

        //opens changeList.csv file to add or delete entries from         Pokemon class
        String changeListfilename = "changeList.csv";
        File changeListFile = new File(changeListfilename);
        Scanner changeScanner = new Scanner(changeListFile);

        //loads text from csv file to be parsed to PokemonNoGaps class
        while(changeScanner.hasNextLine()) {
            String changeLine = changeScanner.nextLine();
            String[] changeStringArray = changeLine.split(", ");
            String action = changeStringArray[0];
            String nameOrId = changeStringArray[1];

            //if changList.csv file line has an "A" in the first spot add this entry to somePokemon
            if(action.equals("A")) {
                int newId = pokedex1.getNewId();
                String name = nameOrId;
                Pokemon somePokemon = new Pokemon(newId, name);
                pokedex1.add(somePokemon);
            }
            //if it has a "D" then send it to PokemonNoGaps class to delete the entry from the array
            else { //"D"
                int someId = Integer.parseInt(nameOrId);
                pokedex1.deleteById(someId);
            }
            //tests the action being taken and the update to the array
            //System.out.println(action + "\t" + nameOrId + "\n");
            System.out.println(pokedex1);

            //*(supposedly)* prints the resulting contents of the array to a new csv file
            String[] pokemonList = changeStringArray;
            try {
                String outputFile1 = "pokedex1.csv";
                FileWriter writer1 = new FileWriter(outputFile1);
                writer1.write(String.valueOf(pokemonList));
            } catch (IOException e) {
                System.out.println("\nError writing to Pokedex1.csv!");
                e.printStackTrace();
            }
        }
        //tests final contents of array after being passed through PokemonNoGaps class
        //System.out.println(pokedex1);

    } catch (FileNotFoundException e) {
        e.printStackTrace();
    }
}

}

PokemonNoGaps 类文件：

public class PokemonNoGaps implements ChangePokedex {
    private Pokemon[] pokedex = new Pokemon[1];
    private int numElements = 0;
    private static int id = 0;
    // add, delete, search

    @Override
    public void add(Pokemon apokemon) {
        // if you have space
        this.pokedex[this.numElements] = apokemon;
        this.numElements++;
        // if you don't have space
        if(this.numElements == pokedex.length) {
            Pokemon[] newPokedex = new Pokemon[ this.numElements * 2]; // create new array
            for(int i = 0; i < pokedex.length; i++) { // transfer all     elements from array into bigger array
                newPokedex[i] = pokedex[i];
            }
            this.pokedex = newPokedex;
        }
        this.id++;
    }

    public int getNewId() {
        return this.id + 1;
    }
    @Override
    public void deleteById(int id) {
        for(int i = 0; i < numElements; i++) {
            if(pokedex[i].getId() == id) {
                for(int j = i+1; j < pokedex.length; j++) {
                    pokedex[j-1] = pokedex[j];
                }
                numElements--;
                pokedex[numElements] = null;
            }
        }
    }

    public Pokemon getFirstElement() {
        return pokedex[0];
    }
    public int getNumElements() {
        return numElements;
    }
    public String toString() {
        String result = "";
        for(int i = 0; i < this.numElements; i++) {
            result += this.pokedex[i].toString() + "\n";
        }
        return result;
    }
}

异常输出：

1, Bulbasaur
3, Venasaur
4, Charizard
5, Squirtle

我是否使用了错误的文件编写器？我是在错误的时间还是错误地调用了文件编写器？换句话说，我不知道为什么我的输出文件是空的并且没有加载我的数组的内容。谁能帮帮我？

Answer 1

String outputFile1 = "pokedex1.csv";
FileWriter writer1 = new FileWriter(outputFile1);

似乎在您的while 循环中，因此每次都会创建一个新文件。

要么使用FileWriter(File file, boolean append)构造函数，要么在循环之前创建

Answer 2

我在运行此程序时发现了一些问题。如上一个答案中所述，您希望在写入新 pokedx1.csv 的代码部分中将 file append 设置为 true

   try {
        String outputFile1 = "pokedex1.csv";
        FileWriter fileWriter = new FileWriter(prefix+outputFile1, true);
        BufferedWriter bw = new BufferedWriter(fileWriter);
        for(String pokemon : pokedex1.toString().split("\n")) {
            System.out.println(pokemon);
            bw.write(pokemon);
        }
        bw.flush();
        bw.close();
   } catch (IOException e) {
        System.out.println("\nError writing to Pokedex1.csv!");
        e.printStackTrace();
   }

我选择使用缓冲阅读器作为解决方案。我发现的另一个问题是您正在阅读 pokedex.csv 但文件名为 pokemon.csv。

String pokedexFilename = "pokemon.csv";

我进行了上述更改以解决此问题。

在旁注中，我注意到您创建了多个扫描仪来读取这两个文件。使用这些类型的资源，在使用完它们后调用 close 方法是一种很好的做法；如下图。

Scanner pokescanner = new Scanner(pokedexFile);
// Use scanner code here
// Once finished with scanner
pokescanner.close();