20非常有用的Java程序片段 (下)

17. 把 Array 转换成 Map 

01.
02. import java.util.Map;
03. import org.apache.commons.lang.ArrayUtils;
04.
05. public class Main {
06.
07.    public static void main(String[] args) {
08.      String[][] countries = { { "United States" , "New York" }, { "United Kingdom" , "London" },
09.          { "Netherland" , "Amsterdam" }, { "Japan" , "Tokyo" }, { "France" , "Paris" } };
10.
11.      Map countryCapitals = ArrayUtils.toMap(countries);
12.
13.      System.out.println( "Capital of Japan is " + countryCapitals.get( "Japan" ));
14.      System.out.println( "Capital of France is " + countryCapitals.get( "France" ));
15.    }
16. }

18. 发送邮件

01. import javax.mail.*;
02. import javax.mail.internet.*;
03. import java.util.*;
04.
05. public void postMail( String recipients[ ], String subject, String message , String from) throws MessagingException
06. {
07.      boolean debug = false ;
08.
09.       //Set the host smtp address
10.       Properties props = new Properties();
11.       props.put( "mail.smtp.host" , "smtp.example.com" );
12.
13.      // create some properties and get the default Session
14.      Session session = Session.getDefaultInstance(props, null );
15.      session.setDebug(debug);
16.
17.      // create a message
18.      Message msg = new MimeMessage(session);
19.
20.      // set the from and to address
21.      InternetAddress addressFrom = new InternetAddress(from);
22.      msg.setFrom(addressFrom);
23.
24.      InternetAddress[] addressTo = new InternetAddress[recipients.length];
25.      for ( int i = 0 ; i < recipients.length; i++)
26.      {
27.          addressTo[i] = new InternetAddress(recipients[i]);
28.      }
29.      msg.setRecipients(Message.RecipientType.TO, addressTo);
30.
31.      // Optional : You can also set your custom headers in the Email if you Want
32.      msg.addHeader( "MyHeaderName" , "myHeaderValue" );
33.
34.      // Setting the Subject and Content Type
35.      msg.setSubject(subject);
36.      msg.setContent(message, "text/plain" );
37.      Transport.send(msg);
38. }

19. 发送代数据的HTTP 请求

01.
02. import java.io.BufferedReader;
03. import java.io.InputStreamReader;
04. import java.net.URL;
05.
06. public class Main {
07.      public static void main(String[] args)  {
08.          try {
09.              URL my_url = new URL( "http://cocre.com/ " );
10.              BufferedReader br = new BufferedReader( new InputStreamReader(my_url.openStream()));
11.              String strTemp = "" ;
12.              while ( null != (strTemp = br.readLine())){
13.              System.out.println(strTemp);
14.          }
15.          } catch (Exception ex) {
16.              ex.printStackTrace();
17.          }
18.      }
19. }

20. 改变数组的大小

01.
02. /**
03. * Reallocates an array with a new size, and copies the contents
04. * of the old array to the new array.
05. * @param oldArray  the old array, to be reallocated.
06. * @param newSize   the new array size.
07. * @return          A new array with the same contents.
08. */
09. private static Object resizeArray (Object oldArray, int newSize) {
10.     int oldSize = java.lang.reflect.Array.getLength(oldArray);
11.     Class elementType = oldArray.getClass().getComponentType();
12.     Object newArray = java.lang.reflect.Array.newInstance(
13.           elementType,newSize);
14.     int preserveLength = Math.min(oldSize,newSize);
15.     if (preserveLength > 0 )
16.        System.arraycopy (oldArray, 0 ,newArray, 0 ,preserveLength);
17.     return newArray;
18. }
19.
20. // Test routine for resizeArray().
21. public static void main (String[] args) {
22.     int [] a = { 1 , 2 , 3 };
23.     a = ( int [])resizeArray(a, 5 );
24.     a[ 3 ] = 4 ;
25.     a[ 4 ] = 5 ;
26.     for ( int i= 0 ; i<a.length; i++)
27.        System.out.println (a[i]);
28. }