常用java工具类

摘自：
http://blog.csdn.net/justdb/article/details/8653166
http://www.cnblogs.com/jifeng/archive/2011/08/16/2140003.html

StringUtils 字符串处理工具类

StringUtils.isEmpty(null) && StringUtils.isEmpty(""); // true 
StringUtils.isBlank("   \n\t");                       // true 
StringUtils.substringAfterLast("foo.bar.baz", ".");   // "baz" 
StringUtils.substringBeforeLast("foo.bar.baz", ".");  // "foo.bar" 
StringUtils.split("foo.bar.baz", '.');                // { "foo", "bar", "baz" } 
StringUtils.split("foo,  bar,baz", ", ");             // { "foo", "bar", "baz" } 
StringUtils.leftPad("1", 3, '0');                     // "001" 



IOUtils and FileUtils

在一种当你需要手动操作多个文件罕见情况下必须具备的工具，这两个工具很相似(FileUtils操作文件，IOUtils操作InputStream和Reader classes)，和捆绑常用IO.


File file1;
File file2;
InputStream inputStream;
OutputStream outputStream;

// copy one file into another
FileUtils.copyFile(file1, file2);
IOUtils.copy(inputStream, outputStream);

// read a file into a String
String s1 = FileUtils.readFileToString(file1);
String s2 = IOUtils.toString(inputStream);

// read a file into a list of Strings, one item per line



List<String> l1 = FileUtils.readLines(file1);
List<String> l2 = IOUtils.readLines(inputStream);

// put this in your finally() clause after manipulating streams
IOUtils.closeQuietly(inputStream);

// return the list of xml and text files in the specified folder and any subfolders
Collection<File> c1 = FileUtils.listFiles(file1, { "xml", "txt" }, true);

// copy one folder and its contents into another
FileUtils.copyDirectoryToDirectory(file1, file2);

// delete one folder and its contents
FileUtils.deleteDirectory(file1);


1.文件内容拷贝：
import java.io.File;
import java.io.FileWriter;
import java.io.IOException;
import java.io.InputStream;
import java.io.Writer;

import org.apache.commons.io.FileUtils;
import org.apache.commons.io.IOUtils;


publicclass FileCopyExample {
    publicstaticvoid main(String[] args) {
       try {
           File src = new File( "test.dat" );
           File dest = new File( "test.dat.bak" );
          
           FileUtils.copyFile( src, dest );
       } catch( IOException ioe ) {
           System.out.println( "Problem copying file." );
       }
      
       try {
           File src = new File( "test.dat" );
           File dir = new File( "./temp" );

           FileUtils.copyFileToDirectory( src, dir );
       } catch( IOException ioe ) {
           System.out.println( "Problem copying file to dir.");
       }
      
       try {
           String string = "Blah blah blah";
           File dest = new File( "test.tmp" );
          
           FileUtils.writeStringToFile( dest, string, "ISO-8859-1" );
       } catch( IOException ioe ) {
           System.out.println( "Error writing out a String." );       
       }
      
      
       try {
           Writer writer = new FileWriter( "test.dat" );
           InputStream inputStream =FileCopyExample.class.
              getClass().getResourceAsStream("/io/web.xml");
           IOUtils.copy( inputStream, writer );
           writer.close();
           inputStream.close();
       } catch (IOException e) {
           System.out.println( "Error copying data" );
       }

try {
           File src = new File( "test.txt" );
           OutputStream output = new FileOutputStream(src);
           InputStream inputStream =FileCopyExample.class.
              getClass().getResourceAsStream("/io/web.xml");
           IOUtils.copy( inputStream, output );
//         writer.close();
           inputStream.close();
           output.close();
       } catch (IOException e) {
           System.out.println( "Error copying data" );
       }
    }

}

2.文件删除：
File file = new File( ("io/project.properties") );
       String display = FileUtils.byteCountToDisplaySize( file.length() );
       System.out.println( "project.xml is " + display );
       FileUtils.forceDelete(file)

3.读取取文本中的每一行：
import java.io.File;
import java.io.IOException;
import java.util.List;

import org.apache.commons.io.FileSystemUtils;
import org.apache.commons.io.FileUtils;


public class Test {

       /**
        * @param args
        * @throws IOException
        */
       public static void main(String[] args) throws IOException {
              // TODO Auto-generated method stub
              File file = new File((Test.class.getClass().getResource("/io/web.xml")).getFile());
               List lines = FileUtils.readLines(file, "UTF-8");
               for(int i=0;i<lines.size();i++)
               System.out.println(lines.get(i));
       }

}