I/O 二:JAVA IO详解（流类）

I/O 2:JAVA IO详解（流类）

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package com.test.Algorithm;

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;

public class FileTest10 {
	//上面提到读数据的步骤为：1，打开一个流。2，判断是否还有数据，并读取数据。3，关闭流。
	public static void main(String[] args) throws IOException {
		//打开流
		FileInputStream fis = new FileInputStream(new File("C:/优秀.txt"));
		byte[] buffer = new byte[200];
		int length = 0;
		//判断是否有更多数据，当没有时，返回-1。
		//上面定义了一个200长度的字节数据，如果test.txt中有500字节长度的数据。
		//那么它会循环4次，lenght的长度分别是200,200,100,-1
		while (-1 != (length = fis.read(buffer, 0, 200))) {
			String s = new String(buffer, 0, length);
			System.out.println(s);
		}
		fis.close();
	}

}

 

InputStream子类中FilterInputStream是过滤流，其它是节点流。

 

以下程序简单演示了FileOutputStream的用法

package com.test.Algorithm;

import java.io.FileOutputStream;
import java.io.IOException;

public class FileTest9 {
	public static void main(String[] args) throws IOException {
		FileOutputStream os = new FileOutputStream("d:/test.txt");
		String str = "hello world";
		byte[] buffer = str.getBytes();
		os.write(buffer);
		os.close();
	}
}

其中FileOutputStream有一个构造函数

FileOutputStream(File file, boolean append) 

参数append表示内容是否追加

 

package com.test.Algorithm;

import java.io.ByteArrayOutputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStream;

public class FileTest9 {
	public static void main(String[] args) throws IOException {
		ByteArrayOutputStream f = new ByteArrayOutputStream();
		String str = "hello world";
		byte[] buffer = str.getBytes();
		f.write(buffer);
		byte[] result = f.toByteArray();
		for (int i = 0; i < result.length; i++) {
			System.out.println((char) result[i]);
		}
		OutputStream os = new FileOutputStream("text.txt");
		f.writeTo(os);
		f.close();
		os.close();
	}
}

 

 

 

package com.test.Algorithm;

import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.ByteArrayOutputStream;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStream;

public class FileTest9 {
	public static void main(String[] args) throws IOException {
		DataOutputStream dos = new DataOutputStream(new BufferedOutputStream(
				new FileOutputStream("a.txt")));
		byte b = 3;
		int i =12;
		char ch ='a';
		float f = 3.3f;
		dos.writeByte(b);
		dos.writeInt(i);
		dos.writeChar(ch);
		dos.writeFloat(f);
		dos.close();
		
		DataInputStream dis = new DataInputStream(new BufferedInputStream(
				new FileInputStream("a.txt")));
		//读与写的顺序要保持一致
		System.out.println(dis.readByte());
		System.out.println(dis.readInt());
		System.out.println(dis.readChar());
		System.out.println(dis.readFloat());
		dis.close();
	}
}

 

package com.test.Algorithm;

import java.io.IOException;
import java.io.InputStream;

public class MyByteArrayInputStream extends InputStream{
	
	protected byte[] data;
	protected int position = 0;
	
	public MyByteArrayInputStream(byte[] b){
		this.data = b;
	}
	
	public int read() throws IOException {
		return (position < data.length) ? (data[position++]) : -1;
	}
	
	public static void main(String[] args) {
		byte[] b = new byte[16];
		for (int i = 0; i < b.length; i++) {
			b[i] = (byte)i;
		}
		MyByteArrayInputStream mbais = new MyByteArrayInputStream(b);
		while(true){
			try {
				int c = mbais.read();
				if(c < 0){
					break;
				}
				System.out.println(c + "  ");
			} catch (IOException e) {
				e.printStackTrace();
			}
		}
	}
}

 

 

package com.test.Algorithm;

import java.io.IOException;
import java.io.InputStream;

public class MyOwnStream extends InputStream{
	protected byte[] data;
	protected int position = 0;
	protected int mark =0;
	public MyOwnStream(byte[] b){
		this.data = b;
	}
	public int read() throws IOException {
		return (position < data.length) ? (data[position++]) : -1;
	}
	//返回仍可读取的字节长度
	public int available() throws IOException {
		return data.length - position;
	}
	
	public void close() throws IOException {
		position = data.length;
	}
	//设置流中的标识位
	public synchronized void mark(int readlimit) {
		this.mark = readlimit;
	}
	//将缓冲流复位到标识位置
	public synchronized void reset() throws IOException {
		if(mark <0 || mark >= data.length){
			throw new IOException("the position is not valid");
		}
		position = mark;
	}
	
	public boolean markSupported() {
		return true;
	}
	
	public int read(byte[] b, int off, int len) throws IOException {
		if(this.position > data.length || len < 0){
			return -1;
		}
		if((this.position + len) > data.length){
			len = data.length - this.position;
		}
		//如果只读0个，就直接返回0
		if(len == 0){
			return 0;
		}
		System.arraycopy(data, position, b, off, len);
		position +=len;
		return len;
	}
	
}

 

学IO最重要的是深刻理解装饰模式！