Java中IO流缓冲区的装饰模式的体现

2022-04-14 15:26:07

一、Java中IO流缓冲区

import java.io.*;
public class BufferedTest
{
public static void copy1()
{
InputStream is = null;
OutputStream os = null;
try
{
is = new FileInputStream("c:\\xy1.jpg");
os = new FileOutputStream("d:\\xy2.jpg");
int len = 0;
byte[] buffer = new byte[1024];
while ((len = is.read(buffer)) != -1)
{
os.write(buffer, 0, len);
}
}
catch (IOException ex)
{
throw new RuntimeException("文件操作出错");
}
finally
{
try
{
if (null != is)
{
is.close();
}
}
catch (IOException ex)
{
throw new RuntimeException("输入流关闭出错");
}

try
{
if (null != os)
{
os.close();
}
}
catch (IOException ex)
{
throw new RuntimeException("输出流关闭出错");
}
}
}

public static void copy2()
{
InputStream is = null;
BufferedInputStream bis = null;
OutputStream os = null;
BufferedOutputStream bos = null;
try
{
is = new FileInputStream("c:\\xy1.jpg");
bis = new BufferedInputStream(is);
os = new FileOutputStream("d:\\xy2.jpg");
bos = new BufferedOutputStream(os);
int len = 0;
byte[] buffer = new byte[1024];
while ((len = bis.read(buffer)) != -1)
{
bos.write(buffer, 0, len);
}
}
catch (IOException ex)
{
throw new RuntimeException("文件操作出错");
}
finally
{
try
{
if (null != bis)
{
bis.close();
}
}
catch (IOException ex)
{
throw new RuntimeException("输入流关闭出错");
}

try
{
if (null != bos)
{
bos.close();
}
}
catch (IOException ex)
{
throw new RuntimeException("输出流关闭出错");
}
}
}
}
copy1方法是普通的利用字节流读写文件的例子。JDK提供了流的缓冲区的概念用来提高读写效率，在copy2中可以提现。利用了设计模式的装饰模式的概念。

二、利用装饰模式自定义读取行方法

字符流的缓冲区BufferedReader提供了读取行的方法，可以一次读取文本文件的一行。利用装饰模式自己实现一个读取行的方法。
public class MyReadLine
{
private Reader reader;

public MyReadLine(Reader reader)
{
super();
this.reader = reader;
}

public String myReadLine() throws IOException
{
// 字符缓冲区
StringBuilder sbuilder = new StringBuilder();
// 单个字符的ASCII码值
int len = 0;
// 未读到文件的末尾
while ((len = reader.read()) != -1)
{
// windows中换行符是\r\n
if (len == '\r') continue;
if (len == '\n')
{
// 读取完了一行，返回该行内容
return sbuilder.toString();
}
else
{
// 将读到的有效字符存入缓冲区
sbuilder.append((char) len);
}
}
// 最后一行可能没有换行符，若判断出现换行符再返回值就读取不到最后一行。故判断缓冲区内是否有值，若有值就返回。
if (sbuilder.length() != 0)
{
return sbuilder.toString();
}
return null;
}

public void myclose() throws IOException
{
reader.close();
}

public Reader getReader()
{
return reader;
}

public void setReader(Reader reader)
{
this.reader = reader;
}
}

public class MyReadLineTest
{
public static void main(String[] args)
{
MyReadLine myReader = null;
try
{
StringBuilder sbresult = new StringBuilder();
myReader = new MyReadLine(new FileReader("c:\\aaa.txt"));
String line = null;
while ((line = myReader.myReadLine()) != null)
{
sbresult.append(line);
}
System.out.println(sbresult.toString());
}
catch (IOException e)
{
throw new RuntimeException("读取文件异常");
}
finally
{
try
{
if (null != myReader)
{
myReader.myclose();
}
}
catch (IOException e)
{
throw new RuntimeException("关闭失败");
}
}
}
}

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