使用printwriter创建一个文本文件，其中包含列表中的几行

Question

我试图以文本格式并使用try and catch创建一个逗号分隔的文件。 为此，我正在使用库PrintWriter。 但是，我还不能互相打印所有行。 我创建了一个列表来存储在每次迭代中创建的每一行，然后尝试在列表上使用for来将每个元素打印为文件中的一行：

for(int i=0;i<listA.size();i++) {
    writer.println(listA.get(i));
}

但是，我在文件中得到的结果是

Name_DS_1,LineString_1,UFI_1,Name_DS_2,LineString_2,UFI_2
Name1,Line1,Ufi1,Name2,Line2,Ufi2

我期望：

Name_DS_1,LineString_1,UFI_1,Name_DS_2,LineString_2,UFI_2
Name1,Line1,Ufi1,Name2,Line2,Ufi2
Name1,Line1,Ufi1,Name2,Line2,Ufi2
Name1,Line1,Ufi1,Name2,Line2,Ufi2

我的整个代码是：

import java.io.File;
import java.io.FileNotFoundException;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

public class App {

    public static List listA = new ArrayList();

    public static void main(String[] args) {
        matchSplits();
    }

    public static void matchSplits()
    {
        String header = "Name_DS_1" + "," + "LineString_1" + "," + "UFI_1" + "," + "Name_DS_2" + "," + "LineString_2" + "," + "UFI_2" + "\r\n";
        String fileName = "D:\\WIP\\test\\Coordinates.txt";  
        File file = new File(fileName);      
        int matchCount = 0;

        try (PrintWriter writer = new PrintWriter(file)) {
            for (int k=0;k<3;k++) {
                //Here I am inserting the header only in the first iteration. 
                if(matchCount == 0) {
                    writer.write(header);
                }

                String Name_DS_1 = "Name1";
                String LineString_1 = "Line1";
                String UFI_1 = "Ufi1";
                String Name_DS_2 = "Name2";
                String LineString_2 = "Line2";
                String UFI_2 = "Ufi2";              
                String line = Name_DS_1 + "," + LineString_1 + "," + UFI_1 + "," + Name_DS_2 + "," + LineString_2 + "," + UFI_2 + "\r\n";

                listA.add(line);

                for(int i=0; i<listA.size(); i++) {
                    writer.println(listA.get(i));
                }

                writer.close();
                matchCount++;
            }                 
        }    
        catch (FileNotFoundException e) {
            System.out.println(e.getMessage());
        }
    }
}

Answer 1

这是您问题的可能解决方案，在这里您可以找到解决方案

public class App {
    public static List<String> listA = new ArrayList<>();
    public static void main(String[] args) {
        matchSplits();
    }
    public static void matchSplits() {
        String header = "Name_DS_1" + "," + "LineString_1" + "," + "UFI_1" + "," + "Name_DS_2" + "," + "LineString_2" + "," + "UFI_2";
        String fileName = "foo.csv"; // your file name here
        File file = new File(fileName);
        try (PrintWriter writer = new PrintWriter(file)) {
            // no need to check if k == 0, this is outside the loop
            listA.add(header);
            // prepare your data here
            for (int k = 0; k < 3; k++) {
                String Name_DS_1 = "Name1";
                String LineString_1 = "Line1";
                String UFI_1 = "Ufi1";
                String Name_DS_2 = "Name2";
                String LineString_2 = "Line2";
                String UFI_2 = "Ufi2";
                String line = Name_DS_1 + "," + LineString_1 + "," + UFI_1 + "," + Name_DS_2 + "," + LineString_2 + "," + UFI_2;
                listA.add(line);
            }
            // write your lines here
            for (String s: listA) {
                writer.println(s);
            }
        } catch (FileNotFoundException e) {
            System.out.println(e.getMessage());
        }
    }
}

一些提示：

• 无需关闭在try(...)声明的PrintWriter
• \\r\\n不需要，因为您已经在使用printline
• 不需要两个计数器， k就足够了（至少在此片段中）

Answer 2

发生这种情况是因为您在for循环范围内编写了writer.close（）。 为（int k = 0; k <3; k ++）

尝试删除writer.close（）语句。 由于该语句仅在k = 0时才关闭写入过程。

因为PrintWriter实例是在try-with-resource语句中声明的，所以无论try语句是正常完成还是突然完成（如果这些资源实现AutoCloseable接口），它将关闭。

尝试这样做，希望它能解决您的问题:)