非常有用的Java程序片段

1.向文件末尾添加内容

BufferedWriter out = null;
try {
    out = new BufferedWriter(new FileWriter(”filename”, true));
    out.write(”aString”);
} catch (IOException e) {
    // error processing code
} finally {
    if (out != null) {
        out.close();
    }
}  

2.得到当前方法的名字

String methodName = Thread.currentThread().getStackTrace()[1].getMethodName();  

3.使用JDBC链接Oracle

public class OracleJdbcTest
{
    String driverClass = "oracle.jdbc.driver.OracleDriver";   

    Connection con;   

    public void init(FileInputStream fs) throws ClassNotFoundException, SQLException, FileNotFoundException, IOException
    {
        Properties props = new Properties();
        props.load(fs);
        String url = props.getProperty("db.url");
        String userName = props.getProperty("db.user");
        String password = props.getProperty("db.password");
        Class.forName(driverClass);   

        con=DriverManager.getConnection(url, userName, password);
    }   

    public void fetch() throws SQLException, IOException
    {
        PreparedStatement ps = con.prepareStatement("select SYSDATE from dual");
        ResultSet rs = ps.executeQuery();   

        while (rs.next())
        {
            // do the thing you do
        }
        rs.close();
        ps.close();
    }   

    public static void main(String[] args)
    {
        OracleJdbcTest test = new OracleJdbcTest();
        test.init();
        test.fetch();
    }
}  

4.把 Java util.Date 转成 sql.Date

java.util.Date utilDate = new java.util.Date();
java.sql.Date sqlDate = new java.sql.Date(utilDate.getTime());  

5.使用NIO进行快速的文件拷贝

public static void fileCopy( File in, File out )
            throws IOException
    {
        FileChannel inChannel = new FileInputStream( in ).getChannel();
        FileChannel outChannel = new FileOutputStream( out ).getChannel();
        try
        {
//          inChannel.transferTo(0, inChannel.size(), outChannel);      // original -- apparently has trouble copying large files on Windows   

            // magic number for Windows, 64Mb - 32Kb)
            int maxCount = (64 * 1024 * 1024) - (32 * 1024);
            long size = inChannel.size();
            long position = 0;
            while ( position < size )
            {
               position += inChannel.transferTo( position, maxCount, outChannel );
            }
        }
        finally
        {
            if ( inChannel != null )
            {
               inChannel.close();
            }
            if ( outChannel != null )
            {
                outChannel.close();
            }
        }
    }  

6.把 Array 转换成 Map

import java.util.Map;
import org.apache.commons.lang.ArrayUtils;   

public class Main {   

  public static void main(String[] args) {
    String[][] countries = { { "United States", "New York" }, { "United Kingdom", "London" },
        { "Netherland", "Amsterdam" }, { "Japan", "Tokyo" }, { "France", "Paris" } };   

    Map countryCapitals = ArrayUtils.toMap(countries);   

    System.out.println("Capital of Japan is " + countryCapitals.get("Japan"));
    System.out.println("Capital of France is " + countryCapitals.get("France"));
  }
}  

7.改变数组的大小

/**
* Reallocates an array with a new size, and copies the contents
* of the old array to the new array.
* @param oldArray  the old array, to be reallocated.
* @param newSize   the new array size.
* @return          A new array with the same contents.
*/
private static Object resizeArray (Object oldArray, int newSize) {
   int oldSize = java.lang.reflect.Array.getLength(oldArray);
   Class elementType = oldArray.getClass().getComponentType();
   Object newArray = java.lang.reflect.Array.newInstance(
         elementType,newSize);
   int preserveLength = Math.min(oldSize,newSize);
   if (preserveLength > 0)
      System.arraycopy (oldArray,0,newArray,0,preserveLength);
   return newArray;
}   

// Test routine for resizeArray().
public static void main (String[] args) {
   int[] a = {1,2,3};
   a = (int[])resizeArray(a,5);
   a[3] = 4;
   a[4] = 5;
   for (int i=0; i<a.length; i++)
      System.out.println (a[i]);
}