Java 使用printwriter创建包含列表中多行的文本文件
我正在尝试创建一个文本格式的逗号分隔文件,并使用try-and-catch。为此,我正在使用库PrintWriter。然而,我还不能把所有的行都打印出来。我创建了一个列表来存储我在每次迭代中创建的每一行,然后我尝试在列表上使用for将每个元素打印为文件中的一行:Java 使用printwriter创建包含列表中多行的文本文件,java,csv,printwriter,Java,Csv,Printwriter,我正在尝试创建一个文本格式的逗号分隔文件,并使用try-and-catch。为此,我正在使用库PrintWriter。然而,我还不能把所有的行都打印出来。我创建了一个列表来存储我在每次迭代中创建的每一行,然后我尝试在列表上使用for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)); } 我期待着: Name_DS_1,LineString_1,UFI_1,Name_DS_2
for(int i=0;i<listA.size();i++) {
writer.println(listA.get(i));
}
我期待着:
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
我的全部代码是:
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());
}
}
}
发生这种情况是因为您在for循环的范围内编写了writer.close。
对于int k=0;这是你问题的可能解决方案,在这里你可以找到解决方案
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());
}
}
}
以下是一些提示:
没有必要像您在try中声明的那样关闭PrintWriter。。。
不需要\r\n因为您已经在使用printline
不需要两个计数器,至少在这个代码段中,k就足够了
该代码执行预期的操作。您似乎只有一行,这意味着它只打印一次该行。要获得更多行,需要添加更多行。writer.close;?for循环的外侧。谢谢@satytnv,这就是错误所在。
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());
}
}
}