java读写文件类总结

一、读文件
String filename = "a.txt";
①//以字节为单位读取文件内容，一次读取一个字节
File file = new File(fileNanme);
InputStream in = new FileInputStream(file);
int tempbyte;
while( (tempbyte=in.read())!=-1 ){
System.out.write(tempbyte);
}


②//以字节为单位读取文件内容，一次读取多个字节
byte[] tempbytes = new byte[100];
InputStream in = new FileInputStream(fileName);
int byteread = 0;
while( (byteread =in.read(tempbyte))!=-1 ){
System.out.write(tempbytes,0,byteread);
}


③//以字符为单位读取文件内容，一次读取一个字符
File file = new File(fileNanme);
Reader reader = new InputeStreamReader(new FileInputStream(file));
int tempchar=0;
while( (tempchar = reader.read())!=-1 ){
System.out.print((char)tempchar);
}


④//以字符为单位读取文件内容，一次读取多个字符
File file = new File(fileNanme);
Reader reader = new InputeStreamReader(new FileInputStream(file));
char[] tempchars= new char[30];
int charread =0 ;//一次性读取的字符个数
while( (charread = reader.read(tempchars))!=-1 ){

}


⑤//以行为单位读取文件内容
File file = new File(fileNanme);
BufferedReader reader = new BufferedReader(new FileReader(file));
String tempString = null;
while( (tempString = reader.readLine())!=null ){
System.out.println(tempString);
}


⑥//随即读取文件内容
RandomAccessFile randomFile = new RandomAccessFile(fileName,"r");
long fileLength = randomFile.length();
int beginIndex = (fileLength >4 ? 4:0);
randomFile.seek(beginIndex);
byte[] bytes = new byte[10];
int byteread = 0;
while( (byteread = randomFile.read(bytes))!=1 ){
System.out.write(bytes,0,byteread);
}




二、写文件
①//以字节为单位写文件
File file = new File(fileNanme);
OutputStream out = new FileOutputStream(file);
String content = "abcdef";
byte[] bytes = content.getBytes();
out.write(bytes);


②//以字符为单位写文件
File file = new File(fileNanme);
Writer writer= new OutpoutStreamWriter(new FileOutputStream(file));
String content = "abcdef";
writer.write(content);


③ //以行为单位写文件
File file = new File(fileNanme);
PrintWriter writer = new PrintWriter(new FileOutputStream(file));
writer.println("文件内容：");
writer.print(155);
writer.print(true);
writer.print("abcd");


④//添加容到文件末尾
String content = "abcdef";
FileWriter writer = new FileWriter(fileName,true);//如果为true则添加到文件末尾；如果为false，则将文件的内容清掉，再将内容添加到文件中
writer.write(content);