Example of file reading and writing
package com.demo;
import java.io.*;
import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;
public class FileUtil {
public static void main(String[] args) throws IOException {
// Overwrite write
PrintWriter writer = new PrintWriter(new FileWriter("data.txt"));
writer.println("hello");
writer.println("world");
writer.close();
// Append write
PrintWriter appendWriter = new PrintWriter(new FileWriter("data.txt", true));
appendWriter.println("hello");
appendWriter.println("world");
appendWriter.close();
// According to the line read
List<String> list = new ArrayList<>();
Scanner scanner = new Scanner(new FileReader("data.txt"));
while (scanner.hasNextLine()) {
String line = scanner.nextLine();
list.add(line);
}
scanner.close();
System.out.println(list);
// [hello, world, hello, world]
}
}
Tool class encapsulation
write in
package com.demo.fileutil;
import java.io.IOException;
import java.io.PrintWriter;
public class FileWriter {
private PrintWriter writer;
public FileWriter(String fileName) throws IOException {
this(fileName, false);
}
public FileWriter(String fileName, boolean append) throws IOException {
this.writer = new PrintWriter(new java.io.FileWriter(fileName, append));
}
public void println(String content){
this.writer.println(content);
}
public void print(String content){
this.writer.print(content);
}
public void close(){
this.writer.close();
}
}
Read
package com.demo.fileutil;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;
public class FileReader {
private String fileName;
public FileReader(String fileName) {
this.fileName = fileName;
}
public List<String> readLines() throws FileNotFoundException {
List<String> list = new ArrayList<>();
Scanner scanner = new Scanner(new java.io.FileReader(this.fileName));
while (scanner.hasNextLine()) {
String line = scanner.nextLine();
list.add(line);
}
scanner.close();
return list;
}
public String readAll() throws IOException {
StringBuilder sb = new StringBuilder();
java.io.FileReader reader = new java.io.FileReader(this.fileName);
int len = 0;
char[] data = new char[1024];
while ((len = reader.read(data)) != -1) {
sb.append(data, 0, len);
}
reader.close();
return sb.toString();
}
}
test
package com.demo;
import com.demo.fileutil.FileReader;
import com.demo.fileutil.FileWriter;
import java.io.IOException;
import java.util.List;
public class TestFileUtil {
public static void main(String[] args) throws IOException {
FileWriter writer = new FileWriter("data.txt", true);
writer.println("hello");
writer.println("world");
writer.close();
FileReader reader = new FileReader("data.txt");
String content = reader.readAll();
System.out.print(content);
// hello
// world
List<String> list = reader.readLines();
System.out.println(list);
// [hello, world]
}
}