前言
Java中读写文件是非常基本的IO操作了，现在总结一下常见的用法。首先总结一下读取文件的步骤：
根据文件的路径获取到文件File对象
将File对象转换成输入流InputStream
将输入流读出来，读的时候Java提供了相应的Reader类
文件流读完之后一定要关闭。
注意：本文文件的字符集都是UTF-8，如果需要字符集转换的请自行处理。
一：字节流读取方式
一般字节流读取方式用在读取图片或者固定格式文件的方式。
如果是一次读取一个字节方式可以用如下方法：
/
* 以字节为单位读取文件内容，一次读取1个字节
*/
@Test
public void inputStream1Test() {
InputStream inputStream = null;
try {
inputStream = new FileInputStream(new File(inputStreamFilePath));
int len;
while ((len = inputStream.read()) != -1) {
System.out.write(len);
}
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} finally {
if (inputStream != null) {
try {
inputStream.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
当然也可以使用缓冲区一次读多个字节
/
* 以字节为单位读取文件内容，一次读取1024个字节
*/
@Test
public void inputStream2Test() {
InputStream inputStream = null;
try {
inputStream = new FileInputStream(new File(inputStreamFilePath));
byte[] temp = new byte[1024];//设置一个1024个字节大小的缓冲区
int byteRead;
while ((byteRead = inputStream.read(temp)) != -1) {
System.out.write(temp, 0, byteRead);
}
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} finally {
if (inputStream != null) {
try {
inputStream.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
二：字符流读取方式
字符流读取方式最常见的就是读取txt文件操作了，原理就是将上面的字节流转换成字符流。
代码示例：
/
* InputStreamReader主要是将字节流转字符流
*/
@Test
public void inputStreamReadTest() {
InputStreamReader inputStreamReader = null;
try {
inputStreamReader = new InputStreamReader(new FileInputStream(new File(inputStreamFilePath)));
int len;
while ((len = inputStreamReader.read()) != -1) {
System.out.print((char) len);
}
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} finally {
if (inputStreamReader != null) {
try {
inputStreamReader.close();
} catch (IOException e) {
e.printStackTrace()java读文件基础;
}
}
}
}
当然字符流也是可以设置缓冲区的
/
* InputStreamReader主要是将字节流转字符流,
* 可以一次读一个缓冲区
*/
@Test
public void inputStreamRead2Test() {
InputStreamReader inputStreamReader = null;
try {
inputStreamReader = new InputStreamReader(new FileInputStream(new File(inputStreamFilePath)));
char[] charBuff = new char[1024];//定义一个1024个字符缓冲区大小
int charRead;
while ((charRead = inputStreamReader.read(charBuff)) != -1) {
System.out.println(new String(charBuff, 0, charRead));
}
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} finally {
if (inputStreamReader != null) {
try {
inputStreamReader.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
三：BufferedReader方式
java中非常实用的给我们提供了缓冲区读取文件的方法，提供了BufferedReader。实用方式如下：
/
* BufferedReader 默认会将字符流读到一个缓冲区，缓冲区默认大小 8192
*/
@Test
public void bufferReaderTest() {
BufferedReader bufferedReader;
try {
bufferedReader = new BufferedReader(new FileReader(new File(inputStreamFilePath)));
int len;
while ((len = bufferedReader.read()) != -1) {
System.out.print((char) len);
}
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
更方便的是BufferedReader中提供了按行读的readLine方法
/
* BufferedReader 默认会将字符流读到一个缓冲区,提供readLine方法，按行读取信息
*/
@Test
public void bufferReader2Test() {
BufferedReader bufferedReader;
try {
bufferedReader = new BufferedReader(new FileReader(new File(inputStreamFilePath)));
String conStr;
while ((conStr = bufferedReader.readLine()) != null) {
System.out.println(conStr);
}
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
三：写文件
直接使用FileOutputStream方式
@Test
public void outputStreamTest() {
OutputStream outputStream = null;
try {
File file = new File(outputStreamFilePath);
outputStream = new FileOutputStream(file);
String hello = "你好,leo825,";
outputStream.write(hello.getBytes());
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} finally {
if (outputStream != null) {
try {
outputStream.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
当然也可以使用直接使用BufferedOutputStream方式
/
* BufferedOutputStream输出流，默认缓冲区8192
*/
@Test
public void bufferedOutputStreamTest() {
BufferedInputStream bufferedInputStream = null;
BufferedOutputStream bufferedOutputStream = null;
try {
File inputStreamFile = new File(inputStreamFilePath);
File outputStreamFile = new File(outputStreamFilePath);
bufferedInputStream = new BufferedInputStream(new FileInputStream(inputStreamFile));
bufferedOutputStream = new BufferedOutputStream(new FileOutputStream(outputStreamFile));
int len;
while ((len = bufferedInputStream.read()) != -1) {
bufferedOutputStream.write(len);
}
bufferedOutputStream.flush();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} finally {
if (bufferedInputStream != null) {
try {
bufferedInputStream.close();
} catch (IOException e) {
e.printStackTrace();
}
}
if (bufferedOutputStream != null) {
try {
bufferedOutputStream.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
四：追加文件内容
方法一：使用FileWriter
/
* 向文件中追加内容
*/
@Test
public void appendFile1Test() {
FileWriter fw = null;
PrintWriter pw = null;
try {
File file = new File(outputStreamFilePath);
fw = new FileWriter(file, true);
pw = new PrintWriter(fw);
pw.append("你好,我是追加内容1 ");
pw.flush();
fw.flush();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} finally {
try {
pw.close();
fw.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
方法二：使用BufferedWriter进行追加
/
* 使用BufferedWriter进行追加
*/
@Test
public void appendFile2Test() {
BufferedWriter bufferedWriter = null;
try {
File file = new File(outputStreamFilePath);
bufferedWriter = new BufferedWriter(new OutputStreamWriter(new FileOutputStream(file, true)));
bufferedWriter.write("你好,我是追加内容2 ");
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} finally {
try {
bufferedWriter.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
方法三：使用RandomAccessFile结合seek方法进行追加
/
* 使用RandomAccessFile结合seek方法进行追加
*/
@Test
public void appendFile3Test() {
RandomAccessFile randomAccessFile = null;
try {
File file = new File(outputStreamFilePath);
randomAccessFile = new RandomAccessFile(file, "rw");//打开一个随机访问文件流，按照读写方式
long fileLength = randomAccessFile.length();//文件的长度，用来寻找文件尾部
randomAccessFile.seek(fileLength);//将写文件指针移动到文件尾部
randomAccessFile.write("你好,我是追加内容3 ".getBytes());
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} finally {
try {
randomAccessFile.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
本文地址：https://blog.csdn.net/u011047968/article/details/107288140
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