java中的包装流和缓冲流概述

处理流/包装流(相对于节点流更高级)装饰设计模式/包装模式:

1:隐藏了底层的节点流的差异,并对外提供了更方便的输入/输出功能,让我们只关心高级流的操作.
2:使用处理流包装了节点流,程序直接操作处理流,让节点流与底层的设备做IO操作.
3:只需要关闭处理流即可.
包装流如何区分:写代码的时候,发现创建对象对象的时候,需要传递另一个流对象.
new 包装流( 流对象 ) ;

什么是缓冲流:

是一个包装流,目的起缓冲作用.BufferedInputStream:BufferedOutputStream:BufferedReader:BufferedWriter:

缓冲流的目的:

操作流的时候,习惯定义一个byte/char数组.
int read():每次都从磁盘文件中读取一个字节. 直接操作磁盘文件性能极低.
解决方案: 定义一个数组作为缓冲区.
byte[] buffer = new byte[1024]; 该数组其实就是一个缓冲区.
一次性从磁盘文件中读取1024个字节. 如此以来,操作磁盘文件的次数少了,—->性能得以提升.
既然我们都能想到,SUN公司早就想到了,提供的默认缓存区大小是8192(1024*8),我们一般不用修改大小.
这里写图片描述

代码：

字节缓冲流案例：

package IO;import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;public class BufferStreamDemo {public static void main(String[] args) throws Exception {File file = new File("file/aaa.txt");BufferedOutputStream out = new BufferedOutputStream(new FileOutputStream(file));out.write("中国".getBytes());out.close();BufferedInputStream in = new BufferedInputStream(new FileInputStream(file));byte[] buffer = new byte[1024];int len = -1;while((len = in.read(buffer)) != -1){System.out.println(new String(buffer, 0, len));}in.close();}
}

字符缓冲流案例：

package IO;import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.FileWriter;public class BufferCharacterDemo {public static void main(String[] args) throws Exception {File file = new File("file/aaa.txt");BufferedWriter in = new BufferedWriter(new FileWriter(file,true));in.newLine();//用来换行等同于‘\n’in.write("美国");in.newLine();in.write("马来西亚");in.close();BufferedReader out = new BufferedReader(new FileReader(file));String line = null;//按行读取while((line = out.readLine()) != null){System.out.println(line);}out.close();}
}

节点流和缓冲流性能对比:

操作字节和字符流都习惯使用缓冲流给包装起来,提供IO性能/效率.

package IO;import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.InputStream;
import java.io.OutputStream;public class NodeStreamVSBufferStream {public static void main(String[] args) throws Exception {//File file = new File("file/0001.酷六网-余光中《写给未来的你》（曹可扬朗诵）[流畅版].flv");File file = new File("file/aaa.txt");File copyFile = new File("file/bbb.txt");printContent(file);//File copyFile = new File("file/《写给未来的你》.flv");test1(file,copyFile);test2(file,copyFile);test3(file,copyFile);test4(file,copyFile);}private static void printContent(File file) throws Exception {BufferedInputStream in = new BufferedInputStream(new FileInputStream(file));byte[] b = new byte[1024];int len = -1;while((len = in.read(b)) != -1){System.out.println(new String(b));}}private static void test4(File file, File copyFile) throws Exception {//测试包装流 ，1024个字节拷贝System.out.println("------------测试包装流 ，1024个字节拷贝---------------");long start = System.currentTimeMillis();BufferedInputStream in = new BufferedInputStream(new FileInputStream(file));BufferedOutputStream out = new BufferedOutputStream(new FileOutputStream(copyFile));int len = -1;byte[] b = new byte[1024];while((len = in.read(b))!= -1){out.write(b);}in.close();out.close();System.out.println(System.currentTimeMillis() - start);}private static void test3(File file, File copyFile) throws Exception{//测试包装流 ，单个个字节拷贝System.out.println("------------测试包装流 ，单个个字节拷贝---------------");long start = System.currentTimeMillis();BufferedInputStream in = new BufferedInputStream(new FileInputStream(file));BufferedOutputStream out = new BufferedOutputStream(new FileOutputStream(copyFile));int len = -1;while((len = in.read())!= -1){out.write(len);}in.close();out.close();System.out.println(System.currentTimeMillis() - start);}private static void test2(File file, File copyFile) throws Exception {//测试字节流 ，存1024个字节拷贝System.out.println("------------测试字节流 ，存1024个字节拷贝---------------");long start = System.currentTimeMillis();InputStream in = new FileInputStream(file);OutputStream out = new FileOutputStream(copyFile);int len = -1;byte[] b = new byte[1024];while((len = in.read(b))!= -1){out.write(b);}in.close();out.close();System.out.println(System.currentTimeMillis() - start);}private static void test1(File file, File copyFile) throws Exception {//测试一个字节一个字节拷贝System.out.println("-----------测试一个字节一个字节拷贝----------------");long start = System.currentTimeMillis();InputStream in = new FileInputStream(file);OutputStream out = new FileOutputStream(copyFile);int len = -1;while((len = in.read())!= -1){out.write(len);}in.close();out.close();System.out.println(System.currentTimeMillis() - start);}
}