读文件用BufferedReader类,写文件用BufferedWriter类。
读文件
读文件需要按顺序创建FileInputStream类、InputStreamReader类、BufferedReader类的实例,具体如下:
FileInputStream fileInputStream = new FileInputStream(file);
InputStreamReader inputStreamReader = new InputStreamReader(fileInputStream, "UTF-8");
BufferedReader bufferedReader = new BufferedReader(inputStreamReader);
读文件时使用BufferedReader的实例,这里是bufferedReader。可以有多种方式读取,比如读取一行:
String line = bufferedReader.readLine();
读取结束时,应当逐一关闭三个对象。关闭的顺序与创建的顺序相反。
bufferedReader.close();
inputStreamReader.close();
fileInputStream.close();
写文件
写文件操作基本与读文件操作一样,只是类的名称有点不同。写文件需要按顺序创建FileOutputStream类、OutputStreamWriter类、BufferedWriter类的实例,具体如下:
FileOutputStream fileOutputStream = new FileOutputStream(newfile);
OutputStreamWriter outputStreamWriter = new OutputStreamWriter(fileOutputStream, "UTF-8");
BufferedWriter bufferedWriter = new BufferedWriter(outputStreamWriter);
写文件时使用
BufferedWriter的实例,这里是bufferedWriter。可以有多种方式写入,比如写一个字符串:
bufferedWriter.write("12345");
写入结束时,应当逐一关闭三个对象。关闭的顺序与创建的顺序相反。
bufferedWriter.close();
outputStreamWriter.close();
fileOutputStream.close();
程序案例
在实际编写程序的时候,应当给读写文件的方法套上try-catch语句。本人用的是eclipse,所以可以很方便地自动添加try-catch语句。这里读者不必关心catch语句的具体内容。import java.io.*;
public class FileIO {
public static void main(String[] args) {
// 文件读取
File file = new File("file.txt");
if (file.exists()) {
try {
// 创建文件输入流(这是一个字节流)
FileInputStream fileInputStream = new FileInputStream(file);
// 创建输入流reader,将字节流转换成字符流,且设置字符编码为UTF-8(这是一个字符流)
InputStreamReader inputStreamReader = new InputStreamReader(fileInputStream, "UTF-8");
// 创建BufferedReader
BufferedReader bufferedReader = new BufferedReader(inputStreamReader);
// 逐行读取
String line;
while ((line = bufferedReader.readLine()) != null) {
System.out.println(line);
}
// 按照与创建相反的顺序关闭对象
bufferedReader.close();
inputStreamReader.close();
fileInputStream.close();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (UnsupportedEncodingException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
// 文件写入
File newfile = new File("newfile.txt");
try {
//创建文件输出流 (字节流)
FileOutputStream fileOutputStream = new FileOutputStream(newfile);
//创建文件输出流(字符流)
OutputStreamWriter outputStreamWriter = new OutputStreamWriter(fileOutputStream, "UTF-8");
//创建文件BufferedWriter
BufferedWriter bufferedWriter = new BufferedWriter(outputStreamWriter);
//输出到文件
bufferedWriter.write("12354");
//按照与创建相反的顺序关闭
bufferedWriter.close();
outputStreamWriter.close();
fileOutputStream.close();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (UnsupportedEncodingException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
}