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常用Java功能代碼

Posted on 2012-05-08 20:15 Xing 閱讀(525) 評論(0) 編輯收藏所屬分類: 基礎

1. 把Strings轉換成int和把int轉換成String

String a = String.valueOf(2);  //integer to numeric string  
int i = Integer.parseInt(a); //numeric  string to an int String a = String.valueOf(2);    //integer to numeric string
int i = Integer.parseInt(a); //numeric string to an int

2. 向Java文件中添加文本

Updated: Thanks Simone for pointing to exception. I have   changed the code. 
BufferedWriter ut = null;  
try   {  
out = new BufferedWriter(new FileWriter(”  filename”, true));  
out.write(”  aString”);  
} catch (IOException e) {  
// error processing code  
} finally   {  
if (out != null) {  
out.close();  
}  
} 
BufferedWriter ut = null;
try {
out = new BufferedWriter(new   FileWriter(”filename”, true));
out.write(”aString”);
} catch   (IOException e) {
// error processing code
} finally {
if (out   != null) {
out.close();
}
}

3. 獲取Java現在正調用的方法名

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

4. 在Java中將String型轉換成Date型

java.util.Date =  java.text.DateFormat.getDateInstance().parse(date String); java.util.Date = java.text.DateFormat.getDateInstance().parse(date  String);or 
SimpleDateFormat format = new SimpleDateFormat( "dd.MM.yyyy"  );  
Date date = format.parse( myString ); 
SimpleDateFormat format = new SimpleDateFormat( "dd.MM.yyyy" );
Date date = format.parse( myString );

5. 通過Java JDBC鏈接Oracle數據庫



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  ();  
}  
} 

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();
}
}

6.將Java中的util.Date轉換成sql.Date

這一片段顯示如何將一個java util Date轉換成sql Date用于數據庫

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

7. 使用NIO快速復制Java文件


public static void fileCopy( File in, File out )    
throws IOException  
{  
FileChannel inChannel = new   FileInputStream( in ).getChannel();  
FileChannel utChannel = 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 )  
{  
&  nbsp; position += inChannel.transferTo( position, maxCount, outChannel ); 

}    
}  
finally 
{  
if (   inChannel != null )  
{  
&  nbsp; inChannel.close();  
}    
if ( outChannel != null )  
{  
&  nbsp;  outChannel.close();  
}    
}  
} 

public static void fileCopy( File in, File out )
throws   IOException
{
FileChannel inChannel = new FileInputStream( in ).getChannel  ();
FileChannel utChannel = 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  ();
}
}
}

8. 在Java中創建縮略圖

private void createThumbnail(String filename, int thumbWidth,   int thumbHeight, intquality, String outFilename)  
throws InterruptedException,   FileNotFoundException, IOException  
{  
// load image from   filename  
Image image =   Toolkit.getDefaultToolkit().getImage(filename);  
MediaTracker mediaTracker = new   MediaTracker(new Container());  
mediaTracker.addImage(image,   0);  
mediaTracker.waitForID(0);  
// use this to test for errors at   this point: System.out.println
(mediaTracker.isErrorAny());  

// determine thumbnail size from   WIDTH and HEIGHT  
double   thumbRatio = (double)thumbWidth / (double)thumbHeight;  
int imageWidth = image.getWidth  (null);  
int imageHeight   = image.getHeight(null);  
double imageRatio = (double)imageWidth / (double)imageHeight;  
if (thumbRatio < imageRatio)   {  
thumbHeight   = (int)(thumbWidth / imageRatio);  
} else {  
thumbWidth =   (int)(thumbHeight * imageRatio);  
}  

// draw original image to thumbnail   image object and  
//   scale it to the new size on-the-fly  
BufferedImage thumbImage = new   BufferedImage(thumbWidth, thumbHeight,
BufferedImage.TYPE_INT_RGB);  
Graphics2D graphics2D =   thumbImage.createGraphics();  
graphics2D.setRenderingHint  (RenderingHints.KEY_INTERPOLATION,
RenderingHints.VALUE_INTERPOLATION_BILINEAR);  
graphics2D.drawImage(image, 0, 0,   thumbWidth, thumbHeight, null);  

// save thumbnail image to   outFilename  
BufferedOutputStream ut = new BufferedOutputStream(new FileOutputStream
(outFilename));  
JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(out);  
JPEGEncodeParam param =   encoder.getDefaultJPEGEncodeParam(thumbImage);  
quality = Math.max(0, Math.min  (quality, 100));  
param.setQuality((float)quality / 100.0f, false);  
encoder.setJPEGEncodeParam  (param);  
encoder.encode  (thumbImage);  
out.close  ();  
} 

private void createThumbnail(String filename, int thumbWidth, int   thumbHeight, int
quality, String outFilename)
throws InterruptedException,   FileNotFoundException, IOException
{
// load image from   filename
Image image = Toolkit.getDefaultToolkit().getImage  (filename);
MediaTracker mediaTracker = new MediaTracker(new   Container());
mediaTracker.addImage(image,   0);
mediaTracker.waitForID(0);
// use this to test   for errors at this point: System.out.println
(mediaTracker.isErrorAny());
// determine thumbnail size from WIDTH and   HEIGHT
double thumbRatio = (double)thumbWidth / (double)  thumbHeight;
int imageWidth = image.getWidth  (null);
int imageHeight = image.getHeight  (null);
double imageRatio = (double)imageWidth / (double)  imageHeight;
if (thumbRatio < imageRatio)   {
thumbHeight = (int)(thumbWidth /   imageRatio);
} else {
thumbWidth = (int)  (thumbHeight * imageRatio);
}
// draw original image to thumbnail image object   and
// scale it to the new size on-the-  fly
BufferedImage thumbImage = new BufferedImage(thumbWidth,
thumbHeight, BufferedImage.TYPE_INT_RGB);
Graphics2D graphics2D =   thumbImage.createGraphics();
graphics2D.setRenderingHint  (RenderingHints.KEY_INTERPOLATION,
RenderingHints.VALUE_INTERPOLATION_BILINEAR);
graphics2D.drawImag  e(image, 0, 0, thumbWidth, thumbHeight, null);
// save thumbnail image to   outFilename
BufferedOutputStream ut = new BufferedOutputStream(new
FileOutputStream(outFilename));
JPEGImageEncoder encoder =   JPEGCodec.createJPEGEncoder(out);
JPEGEncodeParam param =   encoder.getDefaultJPEGEncodeParam
(thumbImage);
quality = Math.max(0, Math.min(quality,   100));
param.setQuality((float)quality / 100.0f,   false);
encoder.setJPEGEncodeParam  (param);
encoder.encode(thumbImage);
out.close  ();
}

9. 在Java中創建JSON數據

Read this article for more details.
Download JAR file json  -rpc-1.0.jar (75 kb)

import org.json.JSONObject;  
...  
...  
JSONObject json = new JSONObject();  
json.put("city", "Mumbai");  
json.put("country",   "India");  
...  
String utput = json.toString  ();  
... 

import org.json.JSONObject;
...
...
JSONObject json = new   JSONObject();
json.put("city", "Mumbai");
json.put("country",   "India");
...
String utput = json.toString();
...

10. 在Java中使用iText JAR打開PDF


Read this article for more details.

import java.io.File;  
import   java.io.FileOutputStream;  
import java.io.OutputStream;  
import java.util.Date;  

import   com.lowagie.text.Document;  
import   com.lowagie.text.Paragraph;  
import   com.lowagie.text.pdf.PdfWriter;  

public class GeneratePDF   {  

public static void main(String[]   args) {  
try   {  
OutputStream   file = new FileOutputStream(new File("C:\\Test.pdf"));  

Document   document = new Document();  
PdfWriter.getInstance(document, file);  
document.open();  
document.add(new Paragraph("Hello Kiran"));  
document.add(new Paragraph(new Date().toString()));  

document.close();  
file.close  ();  

} catch   (Exception e) {  

e.printStackTrace();  
}    
}  
} 

import java.io.File;
import java.io.FileOutputStream;
import   java.io.OutputStream;
import java.util.Date;
import com.lowagie.text.Document;
import   com.lowagie.text.Paragraph;
import com.lowagie.text.pdf.PdfWriter;
public class GeneratePDF {
public static void main(String[] args)   {
try   {
OutputStream file = new FileOutputStream(new File("C:\\Test.pdf"));
Document   document = new Document  ();
PdfWriter.getInstance(document,   file);
document.open  ();
document.add(new Paragraph("Hello   Kiran"));
document.add(new Paragraph(new Date().toString()));
document.close  ();
file.close();
} catch (Exception e) {
e.printStackTrace();
}
}
}

11. 在Java上的HTTP代理設置

System.getProperties().put("http.proxyHost",   "someProxyURL");  
System.getProperties().put("http.proxyPort",   "someProxyPort");  
System.getProperties().put("http.proxyUser",   "someUserName");  
System.getProperties().put("http.proxyPassword",   "somePassword"); 
System.getProperties().put("http.proxyHost",   "someProxyURL");
System.getProperties().put("http.proxyPort",   "someProxyPort");
System.getProperties().put("http.proxyUser",   "someUserName");
System.getProperties().put("http.proxyPassword",   "somePassword");

12. Java Singleton 例子

Read this article for more   details.
Update: Thanks Markus for the comment. I have updated the code and   changed it tomore robust implementation.


public class SimpleSingleton {  
private static SimpleSingleton singleInstance =  new SimpleSingleton  ();  

//Marking default constructor   private  
//to avoid direct   instantiation.  
private SimpleSingleton()   {  
}  

//Get instance for class SimpleSingleton  
public static SimpleSingleton getInstance() {  

return   singleInstance;  
}  
} 

public class SimpleSingleton {
private static SimpleSingleton   singleInstance =  new SimpleSingleton();
//Marking default constructor private
//to avoid direct   instantiation.
private SimpleSingleton() {
}
//Get instance for class SimpleSingleton
public static   SimpleSingleton getInstance() {
return singleInstance;
}
}
One more implementation of   Singleton class. Thanks to Ralph and Lukasz Zielinski
for pointing this out.


public enum SimpleSingleton {  
INSTANCE;  
public void doSomething()   {  
}  
}  

//Call the method from Singleton:  
SimpleSingleton.INSTANCE.doSomething(); 

public enum SimpleSingleton {
INSTANCE;
public void   doSomething() {
}
}
//Call the method from Singleton:
SimpleSingleton.INSTANCE.doSomething();

13. 在Java上做屏幕截圖

Read this article for more details.
import   java.awt.Dimension;  
import java.awt.Rectangle;  
import java.awt.Robot;  
import java.awt.Toolkit;  
import java.awt.image.BufferedImage;  
import   javax.imageio.ImageIO;  
import java.io.File;  

...  

public void captureScreen(String fileName)   throws Exception {  

Dimension screenSize =   Toolkit.getDefaultToolkit().getScreenSize();  
Rectangle   screenRectangle = new Rectangle(screenSize);  
Robot   robot = new Robot();  
BufferedImage image =   robot.createScreenCapture(screenRectangle);  
ImageIO.write(image, "png", new File(fileName));  

}    
... 

import java.awt.Dimension;
import java.awt.Rectangle;
import   java.awt.Robot;
import java.awt.Toolkit;
import   java.awt.image.BufferedImage;
import javax.imageio.ImageIO;
import   java.io.File;
...
public void captureScreen(String fileName) throws Exception {
Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize  ();
Rectangle screenRectangle = new Rectangle  (screenSize);
Robot robot = new Robot();
BufferedImage image = robot.createScreenCapture(screenRectangle);
ImageIO.write(image, "png", new File(fileName));
}
...

14. 在Java中的文件，目錄列表

>File dir = new File("directoryName");  
String[] children = dir.list();  
if (children ==   null) {  
// Either dir does not exist   or is not a directory  
} else {  
for (int i=0; i < children.length; i++)   {  
// Get   filename of file or directory  
String filename =   children[i];  
}  
}  

// It is also possible to filter the   list of returned files.  
// This example does not return any   files that start with `.'.  
FilenameFilter filter = new   FilenameFilter() {  
public boolean   accept(File dir, String name) {  
return !name.startsWith  (".");  
}  
};  
children = dir.list(filter);  

// The list of files can also be retrieved as File objects  
File[] files = dir.listFiles();  

//   This filter only returns directories  
FileFilter fileFilter =   new FileFilter() {  
public boolean   accept(File file) {  
return file.isDirectory  ();  
}  
};  
files = dir.listFiles(fileFilter); 
File dir = new File("directoryName");
String[]   children = dir.list();
if (children == null)   {
// Either dir does not exist or is   not a directory
} else   {
for (int i=0; i <   children.length; i++)   {
// Get   filename of file or   directory
String filename = children[i];
}
}
// It is also possible to filter the list of returned   files.
// This example does not return any files that start   with `.'.
FilenameFilter filter = new FilenameFilter()   {
public boolean accept(File dir,   String name)   {
return !  name.startsWith(".");
}
};
children = dir.list(filter);
// The list of files can also be retrieved as File   objects
File[] files = dir.listFiles();
// This filter only returns directories
FileFilter fileFilter = new FileFilter()   {
public boolean accept(File file)   {
return   file.isDirectory();
}
};
files = dir.listFiles  (fileFilter);

15. 在Java中創建ZIP和JAR文件

 
import java.util.zip.*;  
import   java.io.*;  

public class ZipIt {  
public static void main(String args[]) throws IOException   {  
if (args.length <   2) {  
System.err.println("usage: java ZipIt Zip.zip file1 file2 file3");  
System.exit  (-1);  
}  
File zipFile = new File(args  [0]);  
if   (zipFile.exists()) {  
System.err.println("Zip file already exists, please try another");  
System.exit  (-2);  
}  
FileOutputStream fos = new   FileOutputStream(zipFile);  
ZipOutputStream zos = new   ZipOutputStream(fos);  
int bytesRead;  
byte[]   buffer = new byte[1024];  
CRC32 crc = new CRC32();  
for (int i=1, n=args.length; i < n; i++) {  
String name   = args[i];  
File file =   new File(name);  
if (!  file.exists()) {  
&  nbsp;  System.err.println("Skipping: " + name);  
&  nbsp;  continue;  
}    
BufferedInputStream bis = new BufferedInputStream(  
&  nbsp;  new FileInputStream(file));  
crc.reset  ();  
while   ((bytesRead = bis.read(buffer)) != -1) {  
&  nbsp;  crc.update(buffer, 0, bytesRead);  
}    
bis.close();  
// Reset to   beginning of input stream  
bis = new   BufferedInputStream(  
&  nbsp;  new FileInputStream(file));  
ZipEntry   entry = new ZipEntry(name);  
entry.setMethod(ZipEntry.STORED);  
entry.setCompressedSize(file.length());  
entry.setSize(file.length());  
entry.setCrc(crc.getValue());  
zos.putNextEntry(entry);  
while   ((bytesRead = bis.read(buffer)) != -1) {  
&  nbsp;  zos.write(buffer, 0, bytesRead);  
}    
bis.close();  
}    
zos.close  ();  
}  
} 
import java.util.zip.*;
import java.io.*;
public class ZipIt {
public static void main(String args  []) throws IOException {
if   (args.length < 2)   {
System.err.println("usage: java ZipIt Zip.zip file1 file2   file3");
System.exit(-1);
}
File zipFile = new File(args  [0]);
if (zipFile.exists())   {
System.err.println("Zip file already exists, please try   another");
System.exit(-2);
}
FileOutputStream fos = new   FileOutputStream(zipFile);
ZipOutputStream zos = new ZipOutputStream  (fos);
int   bytesRead;
byte[] buffer = new byte  [1024];
CRC32 crc = new CRC32  ();
for (int i=1, n=args.length; i   < n; i++)   {
String name   = args[i];
File file = new File  (name);
if   (!file.exists())   {
   System.err.println("Skipping: " +   name);
&  nbsp;     continue;
}
BufferedInputStream bis = new BufferedInputStream  (
   new FileInputStream  (file));
crc.reset();
while ((bytesRead = bis.read(buffer)) != -1)   {
   crc.update(buffer, 0,   bytesRead);
}
bis.close  ();
// Reset   to beginning of input   stream
bis =   new BufferedInputStream  (
   new FileInputStream  (file));
ZipEntry entry = new ZipEntry  (name);
entry.setMethod  (ZipEntry.STORED);
&  nbsp; entry.setCompressedSize(file.length  ());
entry.setSize(file.length  ());
entry.setCrc(crc.getValue  ());
zos.putNextEntry  (entry);
while ((bytesRead = bis.read(buffer)) != -1)   {
   zos.write(buffer, 0,   bytesRead);
}
bis.close  ();
}
zos.close();
}
}
16. Parsing / Reading XML file in Java
Sample XML file.


 
 
 
John 
B 
12 
 
 
Mary 
A 
11 
 
 
Simon 
A 
18 
 
 




John
B
12


Mary
A
<  AGE>11


Simon
A
18


Java code to parse above XML.


package net.viralpatel.java.xmlparser;  

import java.io.File;  
import   javax.xml.parsers.DocumentBuilder;  
import   javax.xml.parsers.DocumentBuilderFactory;  

import   org.w3c.dom.Document;  
import org.w3c.dom.Element;  
import org.w3c.dom.Node;  
import   org.w3c.dom.NodeList;  

public class XMLParser   {  

public void getAllUserNames(String   fileName) {  
try   {  
DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();  
DocumentBuilder db = dbf.newDocumentBuilder();  
File file =   new File(fileName);  
if   (file.exists()) {  
&  nbsp;  Document doc = db.parse(file);  
&  nbsp;  Element docEle = doc.getDocumentElement();  

&  nbsp;  // Print root element of the document  
&  nbsp;  System.out.println("Root element of the document: " 
&  nbsp;          + docEle.getNodeName  ());  

&  nbsp;  NodeList studentList = docEle.getElementsByTagName  ("student");  

&  nbsp;  // Print total student elements in document  
&  nbsp;  System.out  
&  nbsp;          .println("Total   students: " + studentList.getLength());  

&  nbsp;  if (studentList != null && studentList.getLength() > 0)   {  
&  nbsp;      for (int i = 0; i < studentList.getLength();   i++) {  

&  nbsp;          Node node =   studentList.item(i);  

&  nbsp;          if (node.getNodeType()   == Node.ELEMENT_NODE) {  

&  nbsp;                System.out  
&  nbsp;                        .println  ("=====================");  

&  nbsp;                Element e = (Element) node;  
&  nbsp;                NodeList nodeList = e.getElementsByTagName("name");  
&  nbsp;                System.out.println("Name: " 
&  nbsp;                        + nodeList.item(0).getChildNodes  ().item(0)  
&  nbsp;                               ;   .getNodeValue());  

&  nbsp;                nodeList = e.getElementsByTagName("grade");  
&  nbsp;                System.out.println("Grade: " 
&  nbsp;                        + nodeList.item(0).getChildNodes  ().item(0)  
&  nbsp;                               ;   .getNodeValue());  

&  nbsp;                nodeList = e.getElementsByTagName("age");  
&  nbsp;                System.out.println("Age: " 
&  nbsp;                        + nodeList.item(0).getChildNodes  ().item(0)  
&  nbsp;                               ;   .getNodeValue());  
&  nbsp;          }  
&  nbsp;      }  
&  nbsp;  } else {  
&  nbsp;      System.exit(1);  
&  nbsp;  }  
}    
} catch (Exception e)   {  
System.out.println(e);  
}  
}  
public   static void main(String[] args) {  

XMLParser parser = new XMLParser  ();  
parser.getAllUserNames("c:\\test.xml");  
}    
} 

package net.viralpatel.java.xmlparser;
import java.io.File;
import javax.xml.parsers.DocumentBuilder;
import   javax.xml.parsers.DocumentBuilderFactory;
import org.w3c.dom.Document;
import org.w3c.dom.Element;
import   org.w3c.dom.Node;
import org.w3c.dom.NodeList;
public class XMLParser {
public void getAllUserNames(String fileName) {
try   {
DocumentBuilderFactory dbf =
DocumentBuilderFactory.newInstance();
DocumentBuilder db =   dbf.newDocumentBuilder();
File file = new File  (fileName);
if (file.exists())   {
Document doc = db.parse  (file);
Element docEle = doc.getDocumentElement();
// Print root element of the   document
System.out.println("Root element of the   document: "
+ docEle.getNodeName());
NodeList studentList = docEle.getElementsByTagName
("student");
// Print total student elements in   document
System.out
&nb  sp;.println("Total students: " +
studentList.getLength());
if (studentList != null &&   studentList.getLength()
> 0) {
for (int i = 0; i <   studentList.getLength
(); i++) {
Node node = studentList.item(i);
if (node.getNodeType() ==
Node.ELEMENT_NODE) {
System.out
     .println
("=====================");
Element e = (Element)   node;
NodeList nodeList =
e.getElementsByTagName  ("name");
System.out.println("Name:   "
+
nodeList.item(0).getChildNodes().item(0)
.getNodeValue());
nodeList =
e.getElementsByTagName  ("grade");
System.out.println("Grade:
"
+
nodeList.item(0).getChildNodes().item(0)
.getNodeValue());
nodeList =
e.getElementsByTagName  ("age");
System.out.println("Age:   "
+
nodeList.item(0).getChildNodes().item(0)
.getNodeValue());
}
}
} else   {
System.exit(1);
}
}
} catch (Exception e)   {
System.out.println(e);
}
}
public static void main(String[] args) {
XMLParser parser = new XMLParser  ();
parser.getAllUserNames("c:\\test.xml");
}
}
17.   Convert Array to Map in Java

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"));  
}  
} 

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"));
}
}
18. Send Email   using Java

import javax.mail.*;  
import   javax.mail.internet.*;  
import java.util.*;  

public void postMail( String recipients[ ], String subject, String message ,   String
from) throws MessagingException  
{  
boolean debug = false;  

//Set the host smtp address  
Properties props = new Properties();  
props.put("mail.smtp.host",   "smtp.example.com");  

// create some   properties and get the default Session  
Session   session = Session.getDefaultInstance(props, null);  
session.setDebug(debug);  

// create a message  
Message msg = new MimeMessage(session);  

// set the from and to address  
InternetAddress addressFrom = new InternetAddress  (from);  
msg.setFrom(addressFrom);  

InternetAddress[] addressTo = new   InternetAddress[recipients.length];  
for (int i =   0; i < recipients.length; i++)  
{  
addressTo[i] = new InternetAddress  (recipients[i]);  
}  
msg.setRecipients(Message.RecipientType.TO,   addressTo);  

// Optional : You can   also set your custom headers in the Email if you Want  
msg.addHeader("MyHeaderName", "myHeaderValue");  

// Setting the Subject and Content   Type  
msg.setSubject(subject);  
msg.setContent(message, "text/plain");  
Transport.send(msg);  
} 

import javax.mail.*;
import javax.mail.internet.*;
import   java.util.*;
public void postMail( String recipients[ ], String subject, String message ,   String
from) throws MessagingException
{
boolean debug =   false;
//Set the host smtp address
Properties props = new Properties();
props.put  ("mail.smtp.host", "smtp.example.com");
// create some properties and get the default   Session
Session session = Session.getDefaultInstance(props,   null);
session.setDebug(debug);
// create a message
Message msg = new   MimeMessage(session);
// set the from and to address
InternetAddress addressFrom = new InternetAddress(from);
msg.setFrom(addressFrom);
InternetAddress[] addressTo = new InternetAddress  [recipients.length];
for (int i = 0; i <   recipients.length; i++)
{
addressTo[i] = new InternetAddress  (recipients[i]);
}
msg.setRecipients  (Message.RecipientType.TO, addressTo);
// Optional : You can also set your custom headers in the   Email if you Want
msg.addHeader("MyHeaderName",   "myHeaderValue");
// Setting the Subject and Content Type
msg.setSubject(subject);
msg.setContent(message,   "text/plain");
Transport.send(msg);
}
19. Send HTTP   request & fetching data using Java

import java.io.BufferedReader;  
import   java.io.InputStreamReader;  
import java.net.URL;  

public class Main {  
public static   void main(String[] args)  {  
try {  
URL my_url =   new URL("BufferedReader br = new BufferedReader(new InputStreamReader
(my_url.openStream()));  
String   strTemp = "";  
while(null   != (strTemp = br.readLine())){  
System.out.println(strTemp);  
}  
} catch (Exception ex) {  
ex.printStackTrace();  
}    
}  
} 

import java.io.BufferedReader;
import   java.io.InputStreamReader;
import java.net.URL;
public class Main {
public static void main(String[] args)    {
try {
URL my_url = new URL("   BufferedReader br = new BufferedReader(new
InputStreamReader(my_url.openStream()));
String strTemp =   "";
while(null != (strTemp = br.readLine()))  {
System.out.println(strTemp);
}
} catch (Exception ex) {
ex.printStackTrace  ();
}
}
}
20. Resize an Array in Java

/** 
* 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 ldSize =   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      System.out.println (a[i]);  
}

16. 在Java中解析/讀取XML文件

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<?xml version="1.0"?> 
<students> 
<student> 
<name>John</name> 
<grade>B</grade> 
<age>12</age> 
</student> 
<student> 
<name>Mary</name> 
<grade>A</grade> 
<age>11</age> 
</student> 
<student> 
<name>Simon</name> 
<grade>A</grade> 
<age>18</age> 
</student> 
</students> 
<?xml version="1.0"?>
<students>
<student>
<name>John</name>
<grade>B</grade>
<age>12</age>
</student>
<student>
<name>Mary</name>
<grade>A</grade>
<age>11</age>
</student>
<student>
<name>Simon</name>
<grade>A</grade>
<age>18</age>
</student>
</students>
Java code to parse above XML.
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package net.viralpatel.java.xmlparser;  

import java.io.File;  
import javax.xml.parsers.DocumentBuilder;  
import javax.xml.parsers.DocumentBuilderFactory;  

import org.w3c.dom.Document;  
import org.w3c.dom.Element;  
import org.w3c.dom.Node;  
import org.w3c.dom.NodeList;  

public class XMLParser {  

public void getAllUserNames(String fileName) {  
try {  
DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();  
DocumentBuilder db = dbf.newDocumentBuilder();  
File file = new File(fileName);  
if (file.exists()) {  
Document doc = db.parse(file);  
Element docEle = doc.getDocumentElement();  

// Print root element of the document  
System.out.println("Root element of the document: " 
+ docEle.getNodeName());  

NodeList studentList = docEle.getElementsByTagName("student");  

// Print total student elements in document  
System.out  
.println("Total students: " + studentList.getLength());  

if (studentList != null && studentList.getLength() > 0) {  
for (int i = 0; i < studentList.getLength(); i++) {  

Node node = studentList.item(i);  

if (node.getNodeType() == Node.ELEMENT_NODE) {  

System.out  
.println("=====================");  

Element e = (Element) node;  
NodeList nodeList = e.getElementsByTagName("name");  
System.out.println("Name: " 
+ nodeList.item(0).getChildNodes().item(0)  
.getNodeValue());  

nodeList = e.getElementsByTagName("grade");  
System.out.println("Grade: " 
+ nodeList.item(0).getChildNodes().item(0)  
.getNodeValue());  

nodeList = e.getElementsByTagName("age");  
System.out.println("Age: " 
+ nodeList.item(0).getChildNodes().item(0)  
.getNodeValue());  
}  
}  
} else {  
System.exit(1);  
}  
}  
} catch (Exception e) {  
System.out.println(e);  
}  
}  
public static void main(String[] args) {  

XMLParser parser = new XMLParser();  
parser.getAllUserNames("c:\\test.xml");  
}  
} 

package net.viralpatel.java.xmlparser;
import java.io.File;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;
public class XMLParser {
public void getAllUserNames(String fileName) {
try {
DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
DocumentBuilder db = dbf.newDocumentBuilder();
File file = new File(fileName);
if (file.exists()) {
Document doc = db.parse(file);
Element docEle = doc.getDocumentElement();
// Print root element of the document
System.out.println("Root element of the document: "
+ docEle.getNodeName());
NodeList studentList = docEle.getElementsByTagName("student");
// Print total student elements in document
System.out
.println("Total students: " + studentList.getLength());
if (studentList != null && studentList.getLength() > 0) {
for (int i = 0; i < studentList.getLength(); i++) {
Node node = studentList.item(i);
if (node.getNodeType() == Node.ELEMENT_NODE) {
System.out
.println("=====================");
Element e = (Element) node;
NodeList nodeList = e.getElementsByTagName("name");
System.out.println("Name: "
+ nodeList.item(0).getChildNodes().item(0)
.getNodeValue());
nodeList = e.getElementsByTagName("grade");
System.out.println("Grade: "
+ nodeList.item(0).getChildNodes().item(0)
.getNodeValue());
nodeList = e.getElementsByTagName("age");
System.out.println("Age: "
+ nodeList.item(0).getChildNodes().item(0)
.getNodeValue());
}
}
} else {
System.exit(1);
}
}
} catch (Exception e) {
System.out.println(e);
}
}
public static void main(String[] args) {
XMLParser parser = new XMLParser();
parser.getAllUserNames("c:\\test.xml");
}
}

17. 在Java中將Array轉換成Map

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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"));  
}  
} 
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"));
}
}

18. 在Java中發送電子郵件

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import javax.mail.*;  
import javax.mail.internet.*;  
import java.util.*;  

public void postMail( String recipients[ ], String subject, String message , String from) throws MessagingException  
{  
boolean debug = false;  

//Set the host smtp address  
Properties props = new Properties();  
props.put("mail.smtp.host", "smtp.example.com");  

// create some properties and get the default Session  
Session session = Session.getDefaultInstance(props, null);  
session.setDebug(debug);  

// create a message  
Message msg = new MimeMessage(session);  

// set the from and to address  
InternetAddress addressFrom = new InternetAddress(from);  
msg.setFrom(addressFrom);  

InternetAddress[] addressTo = new InternetAddress[recipients.length];  
for (int i = 0; i < recipients.length; i++)  
{  
addressTo[i] = new InternetAddress(recipients[i]);  
}  
msg.setRecipients(Message.RecipientType.TO, addressTo);  

// Optional : You can also set your custom headers in the Email if you Want  
msg.addHeader("MyHeaderName", "myHeaderValue");  

// Setting the Subject and Content Type  
msg.setSubject(subject);  
msg.setContent(message, "text/plain");  
Transport.send(msg);  
} 
import javax.mail.*;
import javax.mail.internet.*;
import java.util.*;
public void postMail( String recipients[ ], String subject, String message , String from) throws MessagingException
{
boolean debug = false;
//Set the host smtp address
Properties props = new Properties();
props.put("mail.smtp.host", "smtp.example.com");
// create some properties and get the default Session
Session session = Session.getDefaultInstance(props, null);
session.setDebug(debug);
// create a message
Message msg = new MimeMessage(session);
// set the from and to address
InternetAddress addressFrom = new InternetAddress(from);
msg.setFrom(addressFrom);
InternetAddress[] addressTo = new InternetAddress[recipients.length];
for (int i = 0; i < recipients.length; i++)
{
addressTo[i] = new InternetAddress(recipients[i]);
}
msg.setRecipients(Message.RecipientType.TO, addressTo);
// Optional : You can also set your custom headers in the Email if you Want
msg.addHeader("MyHeaderName", "myHeaderValue");
// Setting the Subject and Content Type
msg.setSubject(subject);
msg.setContent(message, "text/plain");
Transport.send(msg);
}

19. 使用Java發送HTTP請求和提取數據

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import java.io.BufferedReader;  
import java.io.InputStreamReader;  
import java.net.URL;  

public class Main {  
public static void main(String[] args)  {  
try {  
URL my_url = new URL("BufferedReader br = new BufferedReader(new InputStreamReader(my_url.openStream()));  
String strTemp = "";  
while(null != (strTemp = br.readLine())){  
System.out.println(strTemp);  
}  
} catch (Exception ex) {  
ex.printStackTrace();  
}  
}  
} 
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.net.URL;public class Main {
public static void main(String[] args)  {
try {
URL my_url = new URL("BufferedReader br = new BufferedReader(new InputStreamReader(my_url.openStream()));
String strTemp = "";
while(null != (strTemp = br.readLine())){
System.out.println(strTemp);
}
} catch (Exception ex) {
ex.printStackTrace();
}
}
}

20. 在Java中調整數組

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/** 
* 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 ldSize = 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]);  
}

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