java I/O解析 及java.util.zip压缩

1.Java I/O框架采用装饰器模式，可按照读写方式分为字节流和字符流，二者根据数据源的不同都封装了不同的类（ByteArray、String、File、Pipe等），FilterInputStream、FilterOutputStream是用来提供装饰器类接口以控制特定输入流和输出流的两个类。字节流和字符流之间可以通过InputStreamReader和OutPutStreamWriter相互转换。

2.常用案例

import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;

/*
 * 以字符形式缓冲输入一个文件
 */
public class BufferedInputFile {
	static int count = 0;

	//缓冲读取一个指定文件
	public static String read(String fileName){
		StringBuffer sb = new StringBuffer();
		try {
			BufferedReader in = new BufferedReader(new FileReader(new File(fileName)));
			String s;
			while((s = in.readLine()) != null){
				count  = count + 1;
				sb.append(s + "\n");
			}
			in.close();
		} catch (Exception e) {
			e.printStackTrace();
		}
		return sb.toString();
	}

	public static void main(String[] args) {
		System.out.print(read("E:/J2EE/新建文件夹/1.txt"));
		System.out.println("" + count);
	}
}

import java.io.IOException;
import java.io.StringReader;

public class MemoryInput {

	public static void main(String[] args) {
		StringReader in = new StringReader(BufferedInputFile.read("E:/J2EE/新建文件夹/2.txt"));
		int c;
		try {
			while((c = in.read() ) != -1){
				System.out.println((char)c);
			}
			in.close();
		} catch (IOException e) {
			e.printStackTrace();
		}
	}

}

import java.io.ByteArrayInputStream;
import java.io.DataInputStream;
import java.io.EOFException;

public class FormattedMemoryInput {

	public static void main(String[] args) {
		DataInputStream in = new DataInputStream(new ByteArrayInputStream(BufferedInputFile.read("E:/J2EE/新建文件夹/2.txt").getBytes()));
		try{
			while(true){
				System.out.println((char)in.readByte());
			}
		}catch(EOFException e){
			System.out.println("流结束");
			e.printStackTrace();
		}catch(Exception e){
			e.printStackTrace();
		}

	}

}

import java.io.BufferedReader;
import java.io.FileWriter;
import java.io.IOException;
import java.io.StringReader;

/*
 *输出内容到文件中
 */
public class BasicFileOutput {
	public static void main(String[] args) throws IOException {
		BufferedReader in  = new BufferedReader(
				new StringReader(
						BufferedInputFile.read("E:/J2EE/新建文件夹/2.txt")));

		FileWriter out = new FileWriter("E:/J2EE/新建文件夹/2_copy.txt");
		String s;
		while((s = in.readLine()) != null){
			out.write(s + "\r\n");			//在每行结尾添加一个回车换行
		}
		in.close();
		out.close();
	}
}

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

/*
 *使用DataInputStream写入数据
 *使用DataOutputStream恢复数据
 */
public class StoreAndRecoverData {

	public static void main(String[] args) throws IOException {
		DataOutputStream out = new DataOutputStream(new BufferedOutputStream(new FileOutputStream("E:/J2EE/新建文件夹/3.txt")));
		out.writeChars("cc");				//将字符串按字符顺序写入
		out.writeUTF("以UTF形式写入");			//使用utf-8编码写入
		out.writeDouble(3.141659);
		out.writeBoolean(true);
		out.writeInt(1212);
		out.close();

		DataInputStream in = new DataInputStream(new BufferedInputStream(new FileInputStream("E:/J2EE/新建文件夹/3.txt")));
		System.out.println(in.readChar());
		in.skipBytes(2);
		System.out.println(in.readUTF());
		System.out.println(in.readBoolean());
		System.out.println(in.readInt());
	}

}

3.压缩

java.util.zip包中封装了读写压缩格式数据的类，他们大都从java.io包中的相关类继承而来

CheckSum：表示数据校验和的接口，这个包提供了两种校验类型：Adler32、CRC32

CheckedOutputStream(OutputStream out, Checksum cksum) 可以创建一个使用制定校验和的OutputStream

CheckedInputStream(InputStream in, Checksum cksum)
可以创建一个使用制定校验和的InputStream

压缩类：ZipOutputStream : 将数据压缩成zip格式  GZipOutputStream 将数据压缩成gzip格式

解压缩类：ZipInputStram：用于解压缩Zip格式的数据   GZIPInputStram：解压缩GZIP文件格式的数据

例1：使用gzip进行简单压缩

/*
 *使用GZIP进行简单压缩
 */
public class GZIPcompress {

	public static void main(String[] args) throws IOException {
		BufferedReader in = new BufferedReader(new FileReader("E:/J2EE/新建文件夹/2.txt"));

		BufferedOutputStream out = new BufferedOutputStream(new GZIPOutputStream(new FileOutputStream("E:/J2EE/新建文件夹/2.gz")));

		int c;
		while((c = in.read()) != -1)
			out.write(c);
		in.close();
		out.close();

		//GZIPInputStream是字节流，要想使用readLine必须通过InputStreamReader转换
		BufferedReader gin = new BufferedReader(new InputStreamReader(new GZIPInputStream(new FileInputStream("E:/J2EE/新建文件夹/2.gz"))));
		String s;
		while((s = gin.readLine() ) != null){
			System.out.println(s);
		}
	}

}

例2：

/*
 *使用Zip进行多文件压缩
 */
public class ZipCompress {

	public static void main(String[] args) throws IOException {
		FileOutputStream fos = new FileOutputStream("E:/J2EE/新建文件夹/1_2_3.zip");
		CheckedOutputStream cos = new CheckedOutputStream(fos, new Adler32());
		ZipOutputStream zos = new ZipOutputStream(cos);
		BufferedOutputStream out = new BufferedOutputStream(zos);

		zos.setComment("1.txt 2.txt 3.txt的压缩文件");
		String [] fileNames = {"E:/J2EE/新建文件夹/1.txt", "E:/J2EE/新建文件夹/2.txt", "E:/J2EE/新建文件夹/3.txt"};
		for(String name : fileNames){
			BufferedReader in = new BufferedReader(new FileReader(name));

			zos.putNextEntry(new ZipEntry(name));

			int c;
			while((c = in.read()) != -1){
				out.write(c);
			}
			in.close();
			out.flush(); 			//每次循环都应当清空缓冲区（写一次文件），否则会导致所有内容都写到最后一个文件内
		}
		out.close();
	}

}