简单的Java 文件进行读写：一种是stream 一种是reader
第一种是面向字节形式的I/O
第二种就是提供Unicode与面向字符的I/O

//字符流 Reader Writer
//文件字符流 FileReader FileWriter
//缓存字符流 BufferedReader BufferedWiter

//桥接流
//InputStreamReader
//OutputStreamWriter

//字节流InputStream OutputStream
//文件字节流 FileInputStrean FileOutputStream
//缓存字节流 BufferedInputStream BufferedOutputStream
//数据字节流 DataInputStream DataOutputStream
//对象输入流 ObjectInputStream ObjectOutputStream

读：根据InputStream

File file = new File("C:/Users/chen/Desktop/123.txt");
InputStream iStream = new FileInputStream(file);
            byte[] b = new byte[iStream.available()];
            int len = 0;
            while((len = iStream.read(b))!=-1){
                System.out.println(new String(b,0,len));
            }
iStream.close();

读：BufferedReader

BufferedReader br = new BufferedReader(new FileReader(file));
            String str = null;
            StringBuffer sb = new StringBuffer();
            while((str = br.readLine())!=null){
                sb.append(str+"\n");
            }
            System.err.println(sb.toString());
            br.close();

写文件：OutputStream

File file2 = new File("C:/Users/chen/Desktop/test.txt");
OutputStream oStream = new FileOutputStream(file2);
            oStream.write(b);
            oStream.close();