java需要关注的知识点---IO流

1.无论何时使用readLine().都不应该使用DataInputStream,而应该使用BufferedReader.
2.RandomAccessFile，只有RandomAccessFile支持搜索操作，并且只适用于文件。
到jdk1.4中，它的大部分功能被nio存储映射文件所取代。
3.读文件的几种方式：
缓冲输入文件

public class BufferedInputFile {
	public static String read(String file) throws IOException{
		StringBuffer sb = new StringBuffer();
		FileReader fileReader = new FileReader(file);
		BufferedReader br = new BufferedReader(fileReader);
		String s = null;
		while((s = br.readLine()) != null) {
			sb.append(s + "\n");
		}
		return sb.toString();
		
	}
	public static void main(String[] args) {
		try {
			System.out.println(read("D:\\RSA75WP\\test\\src\\com\\io\\BufferedInputFile.java"));
		} catch (IOException e) {
			e.printStackTrace();
		}
	}
}

从内存中输入：

public class MemoryInput {
	
	/**
	 * @param args
	 * @throws IOException 
	 */
	public static void main(String[] args) throws IOException {
		// TODO Auto-generated method stub
		StringReader in = new StringReader(BufferedInputFile
				.read("D:\\RSA75WP\\test\\src\\com\\io\\MemoryInput.java"));
		int c;
		while((c = in.read()) != -1) {
			System.out.print((char)c);
		}
	}

}

格式化的内存输入：

public class FormattedMemoryInput {

	/**
	 * @param args
	 * @throws IOException 
	 */
	public static void main(String[] args) throws IOException {
		DataInputStream dis = new DataInputStream(
				new ByteArrayInputStream(
						(BufferedInputFile
								.read("D:\\RSA75WP\\test\\src\\com\\io\\FormattedMemoryInput.java")
								.getBytes())));
		try {
			while(true) {
				System.out.print((char)dis.readByte());
			}
		} catch (Exception e) {
			System.out.println("End of stream");
		}
	}
	

}

使用available的工作方式会随着所读取的媒介类型不同而有所不同，需要小心使用：

public class TestEof {

	/**
	 * @param args
	 * @throws IOException 
	 */
	public static void main(String[] args) throws IOException {
		DataInputStream in = new DataInputStream(new BufferedInputStream(
				new FileInputStream(
						"D:\\RSA75WP\\test\\src\\com\\io\\TestEof.java")));
		while (in.available() != 0) {
			System.out.println((char)in.readByte());
		}
	}

}

4.写文件：
DataOutputStream:

public class DateOutputStreamTest {
	public static void main(String[] args) throws IOException {
		DataOutputStream dops = new DataOutputStream(new BufferedOutputStream(new FileOutputStream("Data.txt")));
		dops.writeDouble(3.32);
		dops.writeUTF("test outputStream");
		dops.writeInt(4);
		dops.close();
		DataInputStream dis = new DataInputStream(new BufferedInputStream(new FileInputStream("Data.txt")));
		System.out.println(dis.readDouble());
		System.out.println(dis.readUTF());
		System.out.println(dis.readInt());
	}
}	
[b]

RandomAccessFile[/b]

public class UsingRandomAccessFile {
	static String fileNme = "rtest.dat";
	static void display() throws IOException{
		RandomAccessFile raf = new RandomAccessFile(fileNme, "r");
		for ( int i = 0; i< 7 ;i++) {
			System.out.println("Value:" + i + ":" + raf.readDouble());
		}
			System.out.println(raf.readUTF());
			raf.close();
		
	}
	/**
	 * @param args
	 * @throws IOException 
	 */
	public static void main(String[] args) throws IOException {
		RandomAccessFile rf = new RandomAccessFile(fileNme,"rw");
		for(int i = 0; i < 7; i++)
			rf.writeDouble(i*1.414);
		rf.writeUTF("this end of the file");
		rf.close();
		display();
		rf = new RandomAccessFile(fileNme,"rw");
		rf.seek(5*8);
		rf.writeDouble(47.0001);
		rf.close();
		display();
	}

}

读取二进制文件：

public class BinaryFile {
	public static byte[] read(File bFile) throws IOException {
		BufferedInputStream bf = new BufferedInputStream(new FileInputStream(bFile));
		try {
			byte[] data = new byte[bf.available()];
			bf.read(data);
			return data;
		}finally{
			bf.close();
		}
	}
	public static byte[] read(String fileName) throws IOException{
		return read(new File(fileName).getAbsoluteFile());
	}
}