常用的Java代码汇总

http://www.itjhwd.com/java_code/

1. 字符串有整型的相互转换

Java

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

1 2	<strong>Stringa=String.valueOf(2);   //integer to numeric string   inti=Integer.parseInt(a);//numeric string to an int </strong>

2. 向文件末尾添加内容

Java

<strong>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(); } }</strong>

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<strong>BufferedWriter out=null;   try{       out=newBufferedWriter(newFileWriter(”filename”,true));       out.write(”aString”);   }catch(IOExceptione){       // error processing code   }finally{       if(out!=null){           out.close();       }   }</strong>

3. 得到当前方法的名字

Java

<strong>String methodName = Thread.currentThread().getStackTrace()[1].getMethodName(); </strong>

1	<strong>StringmethodName=Thread.currentThread().getStackTrace()[1].getMethodName(); </strong>

4. 转字符串到日期

Java

<strong>java.util.Date = java.text.DateFormat.getDateInstance().parse(date String); </strong>

1	<strong>java.util.Date=java.text.DateFormat.getDateInstance().parse(date String); </strong>

或者是：

Java

<strong>SimpleDateFormat format = new SimpleDateFormat( "dd.MM.yyyy" );   Date date = format.parse( myString ); </strong>

1 2	<strong>SimpleDateFormat format=newSimpleDateFormat("dd.MM.yyyy");   Date date=format.parse(myString); </strong>

5. 使用JDBC链接Oracle

Java

<strong>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();       }   } </strong>

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<strong>publicclassOracleJdbcTest   {       StringdriverClass="oracle.jdbc.driver.OracleDriver";          Connection con;          publicvoidinit(FileInputStream fs)throwsClassNotFoundException,SQLException,FileNotFoundException,IOException       {           Properties props=newProperties();           props.load(fs);           Stringurl=props.getProperty("db.url");           StringuserName=props.getProperty("db.user");           Stringpassword=props.getProperty("db.password");           Class.forName(driverClass);              con=DriverManager.getConnection(url,userName,password);       }          publicvoidfetch()throwsSQLException,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();       }          publicstaticvoidmain(String[]args)       {           OracleJdbcTest test=newOracleJdbcTest();           test.init();           test.fetch();       }   } </strong>

6. 把 Java util.Date 转成 sql.Date

Java

<strong>java.util.Date utilDate = new java.util.Date();   java.sql.Date sqlDate = new java.sql.Date(utilDate.getTime());</strong>

1 2	<strong>java.util.Date utilDate=newjava.util.Date();   java.sql.Date sqlDate=newjava.sql.Date(utilDate.getTime());</strong>

7. 使用NIO进行快速的文件拷贝

Java

<strong>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();               }           }       } </strong>

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<strong>publicstaticvoidfileCopy(File in,File out)               throwsIOException       {           FileChannel inChannel=newFileInputStream(in).getChannel();           FileChannel outChannel=newFileOutputStream(out).getChannel();           try          {   //          inChannel.transferTo(0, inChannel.size(), outChannel);      // original -- apparently has trouble copying large files on Windows                  // magic number for Windows, 64Mb - 32Kb)               intmaxCount=(64*1024*1024)-(32*1024);               longsize=inChannel.size();               longposition=0;               while(position<size)               {                  position+=inChannel.transferTo(position,maxCount,outChannel);               }           }           finally          {               if(inChannel!=null)               {                  inChannel.close();               }               if(outChannel!=null)               {                   outChannel.close();               }           }       } </strong>

8. 创建图片的缩略图

Java

<strong>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();       } </strong>

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<strong>privatevoidcreateThumbnail(Stringfilename,intthumbWidth,intthumbHeight,intquality,StringoutFilename)           throwsInterruptedException,FileNotFoundException,IOException       {           // load image from filename           Image image=Toolkit.getDefaultToolkit().getImage(filename);           MediaTracker mediaTracker=newMediaTracker(newContainer());           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           doublethumbRatio=(double)thumbWidth/(double)thumbHeight;           intimageWidth=image.getWidth(null);           intimageHeight=image.getHeight(null);           doubleimageRatio=(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=newBufferedImage(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=newBufferedOutputStream(newFileOutputStream(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();       } </strong>

9.创建 JSON 格式的数据

并下面这个JAR 文件：json-rpc-1.0.jar (75 kb)

Java

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

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<strong>importorg.json.JSONObject;   ...   ...   JSONObject json=newJSONObject();   json.put("city","Mumbai");   json.put("country","India");   ...   Stringoutput=json.toString();   ...</strong>

10. 使用iText JAR生成PDF

Java

<strong>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();           }       }   } </strong>

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<strong>importjava.io.File;   importjava.io.FileOutputStream;   importjava.io.OutputStream;   importjava.util.Date;      importcom.lowagie.text.Document;   importcom.lowagie.text.Paragraph;   importcom.lowagie.text.pdf.PdfWriter;      publicclassGeneratePDF{          publicstaticvoidmain(String[]args){           try{               OutputStream file=newFileOutputStream(newFile("C:\Test.pdf"));                  Document document=newDocument();               PdfWriter.getInstance(document,file);               document.open();               document.add(newParagraph("Hello Kiran"));               document.add(newParagraph(newDate().toString()));                  document.close();               file.close();              }catch(Exceptione){                  e.printStackTrace();           }       }   } </strong>

11. HTTP 代理设置

Java

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

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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. 单实例Singleton 示例

Java

<strong>   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;       }   } </strong>

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<strong>   publicclassSimpleSingleton{       privatestaticSimpleSingleton singleInstance= newSimpleSingleton();          //Marking default constructor private       //to avoid direct instantiation.       privateSimpleSingleton(){       }          //Get instance for class SimpleSingleton       publicstaticSimpleSingleton getInstance(){              returnsingleInstance;       }   } </strong>

另一种实现

Java

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

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<strong>publicenumSimpleSingleton{       INSTANCE;       publicvoiddoSomething(){       }   }      //Call the method from Singleton:   SimpleSingleton.INSTANCE.doSomething(); </strong>

13. 抓屏程序

Java

<strong>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));      }   ... </strong>

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<strong>importjava.awt.Dimension;   importjava.awt.Rectangle;   importjava.awt.Robot;   importjava.awt.Toolkit;   importjava.awt.image.BufferedImage;   importjavax.imageio.ImageIO;   importjava.io.File;      ...      publicvoidcaptureScreen(StringfileName)throwsException{         Dimension screenSize=Toolkit.getDefaultToolkit().getScreenSize();      Rectangle screenRectangle=newRectangle(screenSize);      Robot robot=newRobot();      BufferedImage image=robot.createScreenCapture(screenRectangle);      ImageIO.write(image,"png",newFile(fileName));      }   ... </strong>

14. 列出文件和目录

Java

<strong>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); </strong>

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<strong>File dir=newFile("directoryName");     String[]children=dir.list();     if(children==null){         // Either dir does not exist or is not a directory     }else{         for(inti=0;i<children.length;i++){             // Get filename of file or directory             Stringfilename=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=newFilenameFilter(){         publicbooleanaccept(File dir,Stringname){             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=newFileFilter(){         publicbooleanaccept(File file){             returnfile.isDirectory();         }     };     files=dir.listFiles(fileFilter); </strong>

15. 创建ZIP和JAR文件

Java

<strong>   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);                   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);               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();       }   } </strong>

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<strong>   importjava.util.zip.*;   importjava.io.*;      publicclassZipIt{       publicstaticvoidmain(Stringargs[])throwsIOException{           if(args.length<2){               System.err.println("usage: java ZipIt Zip.zip file1 file2 file3");               System.exit(-1);           }           File zipFile=newFile(args[0]);           if(zipFile.exists()){               System.err.println("Zip file already exists, please try another");               System.exit(-2);           }           FileOutputStream fos=newFileOutputStream(zipFile);           ZipOutputStream zos=newZipOutputStream(fos);           intbytesRead;           byte[]buffer=newbyte[1024];           CRC32 crc=newCRC32();           for(inti=1,n=args.length;i<n;i++){               Stringname=args[i];               File file=newFile(name);               if(!file.exists()){                   System.err.println("Skipping: "+name);                   continue;               }               BufferedInputStream bis=newBufferedInputStream(                   newFileInputStream(file));               crc.reset();               while((bytesRead=bis.read(buffer))!=-1){                   crc.update(buffer,0,bytesRead);               }               bis.close();               // Reset to beginning of input stream               bis=newBufferedInputStream(                   newFileInputStream(file));               ZipEntry entry=newZipEntry(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){                   zos.write(buffer,0,bytesRead);               }               bis.close();           }           zos.close();       }   } </strong>

16. 解析/读取XML 文件

XML文件

Java

<?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>

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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>

Java代码

Java

   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");       }   }

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packagenet.viralpatel.java.xmlparser;      importjava.io.File;   importjavax.xml.parsers.DocumentBuilder;   importjavax.xml.parsers.DocumentBuilderFactory;      importorg.w3c.dom.Document;   importorg.w3c.dom.Element;   importorg.w3c.dom.Node;   importorg.w3c.dom.NodeList;      publicclassXMLParser{          publicvoidgetAllUserNames(StringfileName){           try{               DocumentBuilderFactory dbf=DocumentBuilderFactory.newInstance();               DocumentBuilder db=dbf.newDocumentBuilder();               File file=newFile(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(inti=0;i<studentList.getLength();i++){                              Node node=studentList.item(i);                              if(node.getNodeType()==Node.ELEMENT_NODE){                                  System.out                                       .println("=====================");                                  Elemente=(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(Exceptione){               System.out.println(e);           }       }       publicstaticvoidmain(String[]args){              XMLParser parser=newXMLParser();           parser.getAllUserNames("c:\test.xml");       }   }

17. 把 Array 转换成 Map 

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"));     }   }

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importjava.util.Map;   importorg.apache.commons.lang.ArrayUtils;      publicclassMain{        publicstaticvoidmain(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. 发送邮件

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);   }

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importjavax.mail.*;   importjavax.mail.internet.*;   importjava.util.*;      publicvoidpostMail(Stringrecipients[],Stringsubject,Stringmessage,Stringfrom)throwsMessagingException   {       booleandebug=false;           //Set the host smtp address        Properties props=newProperties();        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=newMimeMessage(session);          // set the from and to address       InternetAddress addressFrom=newInternetAddress(from);       msg.setFrom(addressFrom);          InternetAddress[]addressTo=newInternetAddress[recipients.length];       for(inti=0;i<recipients.length;i++)       {           addressTo[i]=newInternetAddress(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. 发送代数据的HTTP 请求

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://coolshell.cn/");               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();           }       }   }

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importjava.io.BufferedReader;   importjava.io.InputStreamReader;   importjava.net.URL;      publicclassMain{       publicstaticvoidmain(String[]args) {           try{               URL my_url=newURL("http://coolshell.cn/");               BufferedReader br=newBufferedReader(newInputStreamReader(my_url.openStream()));               StringstrTemp="";               while(null!=(strTemp=br.readLine())){               System.out.println(strTemp);           }           }catch(Exception ex){               ex.printStackTrace();           }       }   }

20. 改变数组的大小

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<a.length; i++)         System.out.println (a[i]);   }

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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.  */  privatestaticObjectresizeArray(ObjectoldArray,intnewSize){      intoldSize=java.lang.reflect.Array.getLength(oldArray);      ClasselementType=oldArray.getClass().getComponentType();      ObjectnewArray=java.lang.reflect.Array.newInstance(            elementType,newSize);      intpreserveLength=Math.min(oldSize,newSize);      if(preserveLength>0)         System.arraycopy(oldArray,0,newArray,0,preserveLength);      returnnewArray;   }      // Test routine for resizeArray().   publicstaticvoidmain(String[]args){      int[]a={1,2,3};      a=(int[])resizeArray(a,5);      a[3]=4;      a[4]=5;      for(inti=0;i<a.length;i++)         System.out.println(a[i]);   }