Commons IO使用

Commons IO提供了org.apache.commons.io.CopyUtils类来将某个InputStream,Reader,byte[]数据或字符串的内容拷贝到OutputStream或Writer.

 Writer writer =  new  FileWriter(  "test.dat"  );
 InputStream inputStream =
     getClass( ).getResourceAsStream("./test.resource" );
 CopyUtils.copy( inputStream, writer );
 writer.close( );
 inputStream.close( );

    Writer writer = new FileWriter( "test.dat" );
    InputStream inputStream = 
        getClass( ).getResourceAsStream("./test.resource");
    CopyUtils.copy( inputStream, writer );
    writer.close( );
    inputStream.close( );

如果需要把信息从Reader或InputStream拷贝到字符串中,请使用IOUtils.toString()方法.

 InputStream inStream = url.openStream( );
 String contents = IOUtils.toString( inStream );

    InputStream inStream = url.openStream( );
    String contents = IOUtils.toString( inStream );

通过org.apache.commons.io.IOUtils,你可以很好地关闭某个InputStream,OutputStream,Reader或Writer,而不必担心null或IOException.

 try  {
     File file = new  File(  "test.dat"  );
     reader = new  FileReader( file );
     result = CopyUtils.toString( reader );
 } catch ( IOException ioe ) {
     System.out.println( "Unable to copy file test.dat to a String."  );
 } finally  {
     IOUtils.closeQuietly( reader );
 }

try {
    File file = new File( "test.dat" );
    reader = new FileReader( file );
    result = CopyUtils.toString( reader );
} catch( IOException ioe ) {
    System.out.println( "Unable to copy file test.dat to a String." );
} finally {
    IOUtils.closeQuietly( reader );
}

使用FileUtils.byteCountToDisplaySize()生成一个字符串,该字符串含有有一个近似的比较好理解的文件的相对大小的值.

 File file =  new  File( "project.xml" );
 long  bytes = file.length( );
 String display = FileUtils.byteCountToDisplaySize( bytes );

   File file = new File("project.xml");
   long bytes = file.length( );
   String display = FileUtils.byteCountToDisplaySize( bytes );

如果需要将一个文件拷贝为另一个文件,或者需要将某个文件拷贝到某一个目录中,可以使用如下的代码:
拷贝为另一个文件:

 File src =  new  File(  "test.dat"  );
 file dest = new  File(  "test.dat.bak"  );
 FileUtils.copyFile( src, dest );

    File src = new File( "test.dat" );
    file dest = new File( "test.dat.bak" );
    FileUtils.copyFile( src, dest );

拷贝到某一个目录:

 File src =  new  File(  "test.dat"  );
 File dir = new  File(  "./temp"  );
 FileUtils.copyFileToDirectory( src, dir );

    File src = new File( "test.dat" );
    File dir = new File( "./temp" );
    FileUtils.copyFileToDirectory( src, dir );

使用Commons IO,你也可以很方便把字符串的内容写入文件中去,具体的过程不用怎么理会:

 String string =  "Blah blah blah" ;
 File dest = new  File(  "test.tmp"  );
 FileUtils.writeStringToFile( dest, string);

  String string = "Blah blah blah";
  File dest = new File( "test.tmp" );
  FileUtils.writeStringToFile( dest, string);

当然,有另外的一个功能,可以将URL的内容存入文件中去:

 URL src =  new  URL(  "http://www.nytimes.com"  );
 File dest = new  File(  "times.html"  );
 FileUtils.copyURLToFile( src, dest );

    URL src = new URL( "http://www.nytimes.com" );
    File dest = new File( "times.html" );
    FileUtils.copyURLToFile( src, dest );

如果你需要删除一个目录下的所有内容(包括其目录),可以这样做:

 File dir =  new  File(  "temp"  );
 FileUtils.deleteDirectory( dir );

    File dir = new File( "temp" );
    FileUtils.deleteDirectory( dir );

如果只想清空目录下所有内容,并不删除该目录,可以这样写:FileUtils.cleanDirectory( dir );


很简单地,可以得到一个目录的大小:

 File dir =  new  File(  "temp"  );
 long  dirSize = FileUtils.sizeOfDirectory( );

File dir = new File( "temp" );
long dirSize = FileUtils.sizeOfDirectory( );

如果你想得到某个目录下所有以.txt结尾的文件,可以如下这样做:

 import  java.io.FilenameFilter;
 import  org.apache.commons.io.filefilter.SuffixFileFilter;
 import  org.apache.commons.lang.ArrayUtils;

 File rootDir = new  File( "." );
 FilenameFilter fileFilter = new  SuffixFileFilter( ".txt" );
 String[] txtFiles = rootDir.list( fileFilter );
 System.out.println( ArrayUtils.toString( txtFiles ) );

import java.io.FilenameFilter;
import org.apache.commons.io.filefilter.SuffixFileFilter;
import org.apache.commons.lang.ArrayUtils;

File rootDir = new File(".");
FilenameFilter fileFilter = new SuffixFileFilter(".txt");
String[] txtFiles = rootDir.list( fileFilter );
System.out.println( ArrayUtils.toString( txtFiles ) );

举另一个例子,怎样列出目录中以.htm和.html结尾的文件

 import  org.apache.commons.io.filefilter.AndFileFilter;
 import  org.apache.commons.io.filefilter.DirectoryFileFilter;
 import  org.apache.commons.io.filefilter.IOFileFilter;
 import  org.apache.commons.io.filefilter.NotFileFilter;
 import  org.apache.commons.io.filefilter.OrFileFilter;
 import  org.apache.commons.io.filefilter.SuffixFileFilter;
 import  org.apache.commons.lang.ArrayUtils;

 IOFileFilter htmlFilter =
     new  OrFileFilter(  new  SuffixFileFilter( "htm" ), new  SuffixFileFilter( "html" ) );  //复合两个SuffixFileFilter
 IOFileFilter notDirectory = new  NotFileFilter( DirectoryFileFilter.INSTANCE );     //拒绝选择目录
 FilenameFilter fileFilter = new  AndFileFilter( htmlFilter, notDirectory );
 String[] htmlFiles = rootDir.list(fileFilter);
 System.out.println( ArrayUtils.toString( htmlFiles ));

import org.apache.commons.io.filefilter.AndFileFilter;
import org.apache.commons.io.filefilter.DirectoryFileFilter;
import org.apache.commons.io.filefilter.IOFileFilter;
import org.apache.commons.io.filefilter.NotFileFilter;
import org.apache.commons.io.filefilter.OrFileFilter;
import org.apache.commons.io.filefilter.SuffixFileFilter;
import org.apache.commons.lang.ArrayUtils;

IOFileFilter htmlFilter = 
    new OrFileFilter( new SuffixFileFilter("htm"),new SuffixFileFilter("html") ); //复合两个SuffixFileFilter
IOFileFilter notDirectory = new NotFileFilter( DirectoryFileFilter.INSTANCE );    //拒绝选择目录
FilenameFilter fileFilter = new AndFileFilter( htmlFilter, notDirectory );
String[] htmlFiles = rootDir.list(fileFilter);
System.out.println( ArrayUtils.toString( htmlFiles ));

注:文中代码来之<<Jakarta Commons Cookbook>>一书第十章