Java中读文件操作

时间:2021-10-21 20:03:18

InputStream & Reader


  • InputStream(字节流),如下是InputStream的层次结构:

Java中读文件操作

public class audioInputStream {
public static void playWAV(){
try {
AudioInputStream stream
= AudioSystem.getAudioInputStream(new File("SourceFile/1.wav"));
byte[] samples = getSamples(stream); //将音频转化为字节数组
InputStream in = new ByteArrayInputStream(samples);
play(in,stream.getFormat());
//播放音频文件
} catch (UnsupportedAudioFileException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}

}
private static byte[] getSamples(AudioInputStream stream){
int length = (int) (stream.getFrameLength()*stream.getFormat().getFrameSize());
byte[] samples = new byte[length];
DataInputStream in
= new DataInputStream(stream);
try {
in.readFully(samples);
System.out.println(length);
}
catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return samples;
}
private static void play(InputStream stream, AudioFormat format){
int bufferSize = format.getFrameSize()* Math.round(format.getSampleRate()/10);
byte[] buffer = new byte[bufferSize];
DataLine.Info info
= new DataLine.Info(SourceDataLine.class, format);
try {
SourceDataLine line
= (SourceDataLine) AudioSystem.getLine(info);
line.open(format, bufferSize);
line.start();
int numBytesRead = 0;
while(numBytesRead != -1){
numBytesRead
= stream.read(buffer, 0, buffer.length);
if(numBytesRead != -1){
line.write(buffer,
0, numBytesRead);
//System.out.println(numBytesRead);
}
}
line.drain();
line.close();
}
catch (LineUnavailableException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
  • ByteArrayInputStream:流的来源并不一定是文件,也可以是内存中的一块空间,例如一个字节数组。ByteArrayInputStream就是将字节数组当作流输入来源的类。
    • new ByteArrayInputStream(byte[] buf, int offset, int length)
    • new ByteArrayInputStream(byte[] buf)
  • FileInputStream:从文件系统或者终端获取输入信息,构造函数如下:
    • new FileInputStream(File file)
    • new FileInputStream(FileDescriptor fdObj)
    • new FileInputStream(String name)
try {
FileInputStream fis
= new FileInputStream("SourceFile/employee");
try {
byte[] bytes = new byte[fis.available()];
fis.read(bytes);
fis.close();
}
catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
catch (FileNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
  • Reader(字符输入流),其层次结构如下:

Java中读文件操作

  • BufferedReader:字符读入,默认拥有8192字符的缓冲区,当BufferedReader在读取文本文件时,会先尽量从文件中读入字符数据并置入缓冲区,而之后若使用read()方法,会先从缓冲区中进行读取。如果缓冲区数据不足,才会再从文件中读取。
    • 构造方法有两个,size表示设置缓冲区大小,默认为8192:
      • new BufferedReader(Reader in)
      • new BufferedReader(Reader in, int size)
    • //System.in是一个位流,为了转换为字符流,可使用InputStreamReader为其进行字符转换,
      //然后再使用BufferedReader为其增加缓冲功能。
      BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
      String content
      = null;
      try {
      while(!(content = br.readLine()).equals("quit")){
      System.out.println(content);
      }
      br.close();
      }
      catch (IOException e) {
      // TODO Auto-generated catch block
      e.printStackTrace();
      }
  • CharArrayReader:从字符数组中读取信息
    • 构造方法有两个:
      • new CharArrayReader(char[] buf)
      • new CharArrayReader(char[] buf, int offset, int length)
    • 相关说明见CharArrayReader类链接。
  • InputStreamReader:将字节流转换为字符流。是字节流通向字符流的桥梁。如果不指定字符集编码,该解码过程将使用平台默认的字符编码。
    • 构造方法:
      • new InputStreamReader(InputStream in)
      • new InputStreamReader(InputStream in, Charset cs)
      • new InputStreamReader(InputStream in, CharsetDecoder dec)
      • new InputStreamReader(InputStream in, String charsetName)
    • 相关说明见InputStreamReader类链接。
  • StringReader:读入String字符串。
    • 构造方法
      • new StringReader(String str)
    • 相关代码
    • StringReader sr = new StringReader("dsfasdfasdfasd");
      char[] chars = new char[5]; //每次读取5个字符
      int length = 0;
      try {
      while((length = sr.read(chars)) != -1){
      String strRead
      = new String(chars, 0, length).toUpperCase();
      System.out.println(strRead);
      }
      }
      catch (IOException e) {
      // TODO Auto-generated catch block
      e.printStackTrace();
      }