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java工程师必备的20个java代码
 学习内容转载 【Gjava人才】www.gjrencai.com 
1. 把Strings转换成int和把int转换成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. 获取java现在正调用的方法名

 

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

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

4. 在java中将String型转换成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. 通过java jdbc链接oracle数据库





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.将java中的util.Date转换成sql.Date

这一片段显示如何将一个java util Date转换成sql Date用于数据库

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快速复制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中创建缩略图

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.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中创建JSON数据

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打开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代理设置

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 to

 


more 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上做屏幕截图

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，目录列表

>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中创建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("http://www.viralpatel.net/blogs/");&nbs
p; 

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("http://www.viralpatel.net/blogs/");

   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/读取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中将Array转换成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中发送电子邮件

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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发送HTTP请求和提取数据

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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("http://www.viralpatel.net/blogs/");  

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("http://www.viralpatel.net/blogs/");

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中调整数组

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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]);  

} 

posted on 2011-01-07 08:47 java_web 阅读(156) 评论(0)  编辑  收藏

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