Java学习笔记40（缓冲流）

缓冲流：

在读写文件的各种流中，最令人烦恼的就是效率问题，

而缓冲流的目的就是提高读写效率

字节输出缓冲流：

package demo;

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

//提高写入效率
public class BufferedOutputStreamDemo {
    public static void main(String[] args) throws IOException {
        FileOutputStream fos = new FileOutputStream("d:\\buffer.txt");
        BufferedOutputStream bos = new BufferedOutputStream(fos);
        bos.write(66);
        byte[] bytes = "HelloWorld".getBytes();
        bos.write(bytes);
        bos.close();
    }
}

字节输入缓冲流：

package demo;

import java.io.BufferedInputStream;
import java.io.FileInputStream;
import java.io.IOException;

public class BufferedInputStreamDemo {
    public static void main(String[] args) throws IOException {
        BufferedInputStream bis = new BufferedInputStream(new FileInputStream("d:\\buffer.txt"));
        byte[] bytes = new byte[10];
        int len = 0;
        while ((len = bis.read(bytes)) != -1) {
            System.out.print(new String(bytes, 0, len));
        }
        bis.close();
    }
}

可以利用缓冲流复制文件，和以前的方法做对比：

并且比较下复制时间

package demo;

import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;

public class Copy {
    public static void main(String[] args) throws IOException {
        long s = System.currentTimeMillis();
        copy1(new File("d:\\LOL.exe"), new File("e:\\LOL.exe"));
        long e = System.currentTimeMillis();
        System.out.println(e - s);// 复制了14154毫秒（14秒）

        copy2(new File("d:\\LOL.exe"), new File("e:\\LOL.exe"));
        // 同样的方法测试时间：129毫秒（0.1秒）

        copy2(new File("d:\\LOL.exe"), new File("e:\\LOL.exe"));
        // 测试时间：94毫秒（不到0.1秒）
    }

    public static void copy1(File src, File desc) throws IOException {
        FileInputStream fis = new FileInputStream(src);
        FileOutputStream fos = new FileOutputStream(desc);
        int len = 0;
        while ((len = fis.read()) != -1) {
            fos.write(len);
        }
        fos.close();
        fis.close();
    }

    public static void copy2(File src, File desc) throws IOException {
        FileInputStream fis = new FileInputStream(src);
        FileOutputStream fos = new FileOutputStream(desc);
        int len = 0;
        byte[] bytes = new byte[1024];
        while ((len = fis.read(bytes)) != -1) {
            fos.write(bytes, 0, len);
        }
        fos.close();
        fis.close();
    }

    public static void copy3(File src, File desc) throws IOException {
        BufferedInputStream bis = new BufferedInputStream(new FileInputStream(src));
        BufferedOutputStream bos = new BufferedOutputStream(new FileOutputStream(desc));
        int len = 0;
        byte[] bytes = new byte[1024 * 10];
        while ((len = bis.read(bytes)) != -1) {
            bos.write(bytes, 0, len);
        }
        bos.close();
        bis.close();
    }
}

字符缓冲输出流：

package demo;

import java.io.BufferedWriter;
import java.io.FileWriter;
import java.io.IOException;

public class BufferedWriterDemo{
    public static void main(String[] args) throws IOException {
        write();
    }
    public static void write() throws IOException{
        FileWriter fw = new FileWriter("d:\\buffer.txt");
        BufferedWriter bfw1 = new BufferedWriter(fw);
        bfw1.write(100);
        bfw1.flush();
        bfw1.write("你好".toCharArray());
        bfw1.newLine();//特有换行方法
        //可以用\r\n换行，不过建议使用这种方法，具有平台无关性
        bfw1.flush();
        bfw1.write("HelloWorld");
        bfw1.flush();
        bfw1.close();
    }
}

字符缓冲输入流：

package demo;

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;

public class BufferedReaderDemo {
    public static void main(String[] args) throws IOException {
        read();
    }

    public static void read() throws IOException {
        int LineNumber = 0;
        BufferedReader bfr1 = new BufferedReader(new FileReader("d:\\read.txt"));
        // 缓冲流特有方法，读取文本单行
        String line = null;
        while ((line = bfr1.readLine()) != null) {
            LineNumber++;
            System.out.println("第" + LineNumber + "行的内容：" + line);
        }
        bfr1.close();
    }
}

字符缓冲流复制文本文件：

package demo;

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;

public class Copy {
    public static void main(String[] args) throws IOException {
        BufferedReader bfr1 = new BufferedReader(new FileReader("d:\\read.txt"));
        BufferedWriter bfw1 = new BufferedWriter(new FileWriter("e:\\read.txt"));
        String line = null;
        while ((line = bfr1.readLine()) != null) {
            bfw1.write(line);
            bfw1.newLine();
            bfw1.flush();
        }
        bfw1.close();
        bfr1.close();
    }
}

关于各种流的操作规律和选用：

1.明确是要读取还是写入（源和目的）

2.明确是要操作什么类型的，字节还是文本？

3.明确数据所在的设备，在硬盘中还是内存中，或者是网络？（这里还没有介绍内存流和socket）

4.是否需要编码转换，需要利用缓冲流、数组提高效率码？