java IO实现一次性读取一个文件全部内容后在写入一个文件

import java.io.*;/*** @author admin*/
public class FileIo {public static void main(String[] args) {String content = getFileString();File outputFile = new File("C:\\Users\\admin\\Desktop\\test\\1.txt");try (FileOutputStream fileOutputStream = new FileOutputStream(outputFile);BufferedWriter bufferedWriter = new BufferedWriter(new OutputStreamWriter(fileOutputStream))) {bufferedWriter.write(content);bufferedWriter.flush(); // 确保所有内容都被写入} catch (IOException e) {e.printStackTrace();}}public static String getFileString(){StringBuilder contentBuilder = new StringBuilder();File file = new File("C:\\Users\\admin\\Desktop\\test\\2.txt");FileInputStream fileInputStream = null;InputStreamReader inputStreamReader = null;BufferedReader bufferedReader = null;String content = "";try {fileInputStream = new FileInputStream(file);inputStreamReader = new InputStreamReader(fileInputStream);bufferedReader = new BufferedReader(inputStreamReader);String line;while ((line = bufferedReader.readLine()) != null) {contentBuilder.append(line);contentBuilder.append(System.lineSeparator());}content = contentBuilder.toString();} catch (IOException e) {e.printStackTrace();}finally {try {if (bufferedReader != null) {bufferedReader.close();}} catch (IOException e) {e.printStackTrace();}try {if (inputStreamReader != null) {inputStreamReader.close();}} catch (IOException e) {e.printStackTrace();}try {if (fileInputStream != null) {fileInputStream.close();}} catch (IOException e) {e.printStackTrace();}}return  content;}
}