20 명의 개발 자가 매우 유용 한 자바 기능 코드

56866 단어 자바Oaclejsonxml.net
1.Strings 를 int 로 변환 하고 int 를 String 으로 변환
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.자바 파일 에 텍스트 추가
 
 
Updated: Thanks Simone for pointing to exception. I have 

changed the code.  
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();   


}   
}  

 

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(); } }


 
 
3.자바 가 현재 호출 중인 방법 명 가 져 오기
  
String methodName =
Thread.currentThread().getStackTrace()[1].getMethodName();  

 

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


4.자바 에서 String 형 을 Date 형 으로 변환
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.Java JDBC 를 통 해 Oracle 데이터베이스 연결
 


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.자바 의 util.Date 를 sql.Date 로 변환
이 세 션 은 자바 util Date 를 sql Date 로 데이터베이스 에 사용 하 는 방법 을 보 여 줍 니 다.
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.NIO 를 사용 하여 자바 파일 을 빠르게 복사
 
 
 
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 )   {   & 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 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 (); } } }


 
 
 
8.자바 에 미리 보기 그림 만 들 기
 
 
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 out = 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 out = 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.자바 에서 JSON 데이터 만 들 기
 
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 output = json.toString ();   ... 

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


10.자바 에서 iText JAR 로 PDF 열기
 

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.자바 에 있 는 HTTP 프 록 시 설정
 
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 싱글 톤 의 예
 
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.자바 에서 화면 캡 처 하기
 
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.자바 에 있 는 파일,디 렉 터 리 목록
 
>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.자바 에서 ZIP 과 JAR 파일 만 들 기
 
  
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.

<!--l version="1.0-->      John  B  12      Mary  A  11      Simon  A  18     

<!--l version="1.0"? --> 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 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      System.out.println (a[i]);   } 


 
16.자바 에서 XML 파일 해석/읽 기
 
 
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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.

view plaincopy to clipboardprint? 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.자바 에서 Array 를 Map 으로 변환
 
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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.자바 에서 이메일 보 내기
 
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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.자바 로 HTTP 요청 및 데이터 추출
 
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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.자바 에서 배열 조정
 
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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 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]);   
}  

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