20个非常有用的Java程序片段

                                                  20个非常有用的Java程序片段-北京尚学堂

下面是20个非常有用的Java程序片段，希望能对你有用。

　　1. 字符串有整型的相互转换

1 2	String a = String.valueOf(2);   //integer to   numeric string  int i = Integer.parseInt(a); //numeric string to an int

　　2. 向文件末尾添加内容

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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. 得到当前方法的名字

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

　　4. 转字符串到日期

1

<span id="12_nwp" style="width: auto;   height: auto; float: none;"><a id="12_nwl" href="http://cpro.baidu.com/cpro/ui/uijs.php?adclass=0&app_id=0&c=news&cf=1001&ch=0&di=128&fv=20&is_app=0&jk=5a3764283252b2ed&k=java&k0=java&kdi0=0&luki=3&mcpm=0&n=10&p=baidu&q=06011078_cpr&rb=0&rs=1&seller_ id=1&sid=edb252322864375a&ssp2=1&stid=9&t=tpclicked3_hc&td=1922429&tu=u1922429&u=http%3A%2F%2Fwww%2Eadmin10000%2Ecom%2Fdocument%2F6065%2Ehtml&urlid=0"   target="_blank" mpid="12" style="text-decoration:   none;"><span   style="color:#0000ff;font-size:14px;width:auto;height:auto;float:none;">java</span></a></span>.util.Date   = java.text.DateFormat .getDateInstance().parse(date String);

　　或者是：

1 2	SimpleDateFormat format = new SimpleDateFormat(   "dd.MM.yyyy" );  Date date = format.parse( myString );

　　5. 使用JDBC链接Oracle

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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. 把 Java util.Date 转成 sql.Date

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<span id="11_nwp" style="width: auto;   height: auto; float: none;"><a id="11_nwl" href="http://cpro.baidu.com/cpro/ui/uijs.php?adclass=0&app_id=0&c=news&cf=1001&ch=0&di=128&fv=20&is_app=0&jk=5a3764283252b2ed&k=java&k0=java&kdi0=0&luki=3&mcpm=0&n=10&p=baidu&q=06011078_cpr&rb=0&rs=1&seller_ id=1&sid=edb252322864375a&ssp2=1&stid=9&t=tpclicked3_hc&td=1922429&tu=u1922429&u=http%3A%2F%2Fwww%2Eadmin10000%2Ecom%2Fdocument%2F6065%2Ehtml&urlid=0"   target="_blank" mpid="11" style="text-decoration:   none;"><span style="color:#0000ff;font-size:14px;width:auto;height:auto;float:none;">java</span></a></span>.util.Date   utilDate = new java.util.Date();  java.sql.Date sqlDate = new   java.sql.Date(utilDate.getTime());

　　7. 使用NIO进行快速的文件拷贝

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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. 创建图片的缩略图

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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          <span   id="10_nwp" style="width: auto; height: auto; float:   none;"><a id="10_nwl" href="http://cpro.baidu.com/cpro/ui/uijs.php?adclass=0&app_id=0&c=news&cf=1001&ch=0&di=128&fv=20&is_app=0&jk=5a3764283252b2ed&k=double&k0=double&kdi0=0&luki=2&mcpm=0&n=10&p=baidu&q=06011078_cpr&rb=0&rs=1&seller_ id=1&sid=edb252322864375a&ssp2=1&stid=9&t=tpclicked3_hc&td=1922429&tu=u1922429&u=http%3A%2F%2Fwww%2Eadmin10000%2Ecom%2Fdocument%2F6065%2Ehtml&urlid=0"   target="_blank" mpid="10" style="text-decoration:   none;"><span   style="color:#0000ff;font-size:14px;width:auto;height:auto;float:none;">double</span></a></span>   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();        }

　　9. 创建 JSON 格式的数据

　　请先阅读这篇文章 了解一些细节，

　　并下面这个JAR 文件：json-rpc-1.0.jar (75 kb)

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

　　10. 使用iText JAR生成PDF

　　阅读这篇文章 了解更多细节

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import <span id="9_nwp" style="width:   auto; height: auto; float: none;"><a id="9_nwl"   href="http://cpro.baidu.com/cpro/ui/uijs.php?adclass=0&app_id=0&c=news&cf=1001&ch=0&di=128&fv=20&is_app=0&jk=5a3764283252b2ed&k=java&k0=java&kdi0=0&luki=3&mcpm=0&n=10&p=baidu&q=06011078_cpr&rb=0&rs=1&seller_ id=1&sid=edb252322864375a&ssp2=1&stid=9&t=tpclicked3_hc&td=1922429&tu=u1922429&u=http%3A%2F%2Fwww%2Eadmin10000%2Ecom%2Fdocument%2F6065%2Ehtml&urlid=0"   target="_blank" mpid="9" style="text-decoration:   none;"><span   style="color:#0000ff;font-size:14px;width:auto;height:auto;float:none;">java</span></a></span>.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. HTTP 代理设置

　　阅读这篇 文章 了解更多细节。

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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

　　请先阅读这篇文章 了解更多信息

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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;      }  }

　　另一种实现

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

　　13. 抓屏程序

　　阅读这篇文章 获得更多信息。

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import <span id="8_nwp" style="width:   auto; height: auto; float: none;"><a id="8_nwl"   href="http://cpro.baidu.com/cpro/ui/uijs.php?adclass=0&app_id=0&c=news&cf=1001&ch=0&di=128&fv=20&is_app=0&jk=5a3764283252b2ed&k=java&k0=java&kdi0=0&luki=3&mcpm=0&n=10&p=baidu&q=06011078_cpr&rb=0&rs=1&seller_ id=1&sid=edb252322864375a&ssp2=1&stid=9&t=tpclicked3_hc&td=1922429&tu=u1922429&u=http%3A%2F%2Fwww%2Eadmin10000%2Ecom%2Fdocument%2F6065%2Ehtml&urlid=0"   target="_blank" mpid="8" style="text-decoration:   none;"><span   style="color:#0000ff;font-size:14px;width:auto;height:auto;float:none;">java</span></a></span>.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. 列出文件和目录

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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. 创建ZIP和JAR文件

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import <span id="7_nwp" style="width:   auto; height: auto; float: none;"><a id="7_nwl"   href="http://cpro.baidu.com/cpro/ui/uijs.php?adclass=0&app_id=0&c=news&cf=1001&ch=0&di=128&fv=20&is_app=0&jk=5a3764283252b2ed&k=java&k0=java&kdi0=0&luki=3&mcpm=0&n=10&p=baidu&q=06011078_cpr&rb=0&rs=1&seller_ id=1&sid=edb252322864375a&ssp2=1&stid=9&t=tpclicked3_hc&td=1922429&tu=u1922429&u=http%3A%2F%2Fwww%2Eadmin10000%2Ecom%2Fdocument%2F6065%2Ehtml&urlid=0"   target="_blank" mpid="7" style="text-decoration:   none;"><span   style="color:#0000ff;font-size:14px;width:auto;height:auto;float:none;">java</span></a></span>.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();        }  }

　　16. 解析/读取XML 文件

　　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>

　　Java代码

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package net.viralpatel.<span id="4_nwp"   style="width: auto; height: auto; float: none;"><a   id="4_nwl" href="http://cpro.baidu.com/cpro/ui/uijs.php?adclass=0&app_id=0&c=news&cf=1001&ch=0&di=128&fv=20&is_app=0&jk=5a3764283252b2ed&k=java&k0=java&kdi0=0&luki=3&mcpm=0&n=10&p=baidu&q=06011078_cpr&rb=0&rs=1&seller_ id=1&sid=edb252322864375a&ssp2=1&stid=9&t=tpclicked3_hc&td=1922429&tu=u1922429&u=http%3A%2F%2Fwww%2Eadmin10000%2Ecom%2Fdocument%2F6065%2Ehtml&urlid=0"   target="_blank" mpid="4" style="text-decoration:   none;"><span   style="color:#0000ff;font-size:14px;width:auto;height:auto;float:none;">java</span></a></span>.<span   id="5_nwp" style="width: auto; height: auto; float:   none;"><a id="5_nwl" href="http://cpro.baidu.com/cpro/ui/uijs.php?adclass=0&app_id=0&c=news&cf=1001&ch=0&di=128&fv=20&is_app=0&jk=5a3764283252b2ed&k=xml&k0=xml&kdi0=0&luki=1&mcpm=0&n=10&p=baidu&q=06011078_cpr&rb=0&rs=1&seller_ id=1&sid=edb252322864375a&ssp2=1&stid=9&t=tpclicked3_hc&td=1922429&tu=u1922429&u=http%3A%2F%2Fwww%2Eadmin10000%2Ecom%2Fdocument%2F6065%2Ehtml&urlid=0"   target="_blank" mpid="5" style="text-decoration:   none;"><span   style="color:#0000ff;font-size:14px;width:auto;height:auto;float:none;">xml</span></a></span>parser;      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.<span   id="6_nwp" style="width: auto; height: auto; float:   none;"><a id="6_nwl"   href="http://cpro.baidu.com/cpro/ui/uijs.php?adclass=0&app_id=0&c=news&cf=1001&ch=0&di=128&fv=20&is_app=0&jk=5a3764283252b2ed&k=xml&k0=xml&kdi0=0&luki=1&mcpm=0&n=10&p=baidu&q=06011078_cpr&rb=0&rs=1&seller_id=1&s id=edb252322864375a&ssp2=1&stid=9&t=tpclicked3_hc&td=1922429&tu=u1922429&u=http%3A%2F%2Fwww%2Eadmin10000%2Ecom%2Fdocument%2F6065%2Ehtml&urlid=0"   target="_blank" mpid="6" style="text-decoration:   none;"><span   style="color:#0000ff;font-size: 14px;width:auto;height:auto;float:none;">xml</span></a></span>");        }  }

　　17. 把 Array 转换成 Map 

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import <span id="3_nwp" style="width:   auto; height: auto; float: none;"><a id="3_nwl"   href="http://cpro.baidu.com/cpro/ui/uijs.php?adclass=0&app_id=0&c=news&cf=1001&ch=0&di=128&fv=20&is_app=0&jk=5a3764283252b2ed&k=java&k0=java&kdi0=0&luki=3&mcpm=0&n=10&p=baidu&q=06011078_cpr&rb=0&rs=1&seller _id=1&sid=edb252322864375a&ssp2=1&stid=9&t=tpclicked3_hc&td=1922429&tu=u1922429&u=http%3A%2F%2Fwww%2Eadmin10000%2Ecom%2Fdocument%2F6065%2Ehtml&urlid=0"   target="_blank" mpid="3" style="text-decoration:   none;"><span   style="color:#0000ff;font-size:14px;width:auto;height:auto;float:none;">java</span></a></span>.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. 发送邮件

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import <span id="2_nwp" style="width:   auto; height: auto; float: none;"><a id="2_nwl"   href="http://cpro.baidu.com/cpro/ui/uijs.php?adclass=0&app_id=0&c=news&cf=1001&ch=0&di=128&fv=20&is_app=0&jk=5a3764283252b2ed&k=java&k0=java&kdi0=0&luki=3&mcpm=0&n=10&p=baidu&q=06011078_cpr&rb=0&rs=1&seller _id=1&sid=edb252322864375a&ssp2=1&stid=9&t=tpclicked3_hc&td=1922429&tu=u1922429&u=http%3A%2F%2Fwww%2Eadmin10000%2Ecom%2Fdocument%2F6065%2Ehtml&urlid=0"   target="_blank" mpid="2" style="text-decoration:   none;"><span style="color:#0000ff;font-size:14px;width:auto;height:auto;float:none;">java</span></a></span>x.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. 发送代数据的HTTP 请求

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import <span id="1_nwp" style="width:   auto; height: auto; float: none;"><a id="1_nwl"   href="http://cpro.baidu.com/cpro/ui/uijs.php?adclass=0&app_id=0&c=news&cf=1001&ch=0&di=128&fv=20&is_app=0&jk=5a3764283252b2ed&k=java&k0=java&kdi0=0&luki=3&mcpm=0&n=10&p=baidu&q=06011078_cpr&rb=0&rs=1&seller_ id=1&sid=edb252322864375a&ssp2=1&stid=9&t=tpclicked3_hc&td=1922429&tu=u1922429&u=http%3A%2F%2Fwww%2Eadmin10000%2Ecom%2Fdocument%2F6065%2Ehtml&urlid=0"   target="_blank" mpid="1" style="text-decoration:   none;"><span style="color:#0000ff;font-size:14px;width:auto;height:auto;float:none;">java</span></a></span>.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();            }        }  }

　　20. 改变数组的大小

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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 = <span   id="0_nwp" style="width: auto; height: auto; float:   none;"><a id="0_nwl" href="http://cpro.baidu.com/cpro/ui/uijs.php?adclass=0&app_id=0&c=news&cf=1001&ch=0&di=128&fv=20&is_app=0&jk=5a3764283252b2ed&k=java&k0=java&kdi0=0&luki=3&mcpm=0&n=10&p=baidu&q=06011078_cpr&rb=0&rs=1&seller_ id=1&sid=edb252322864375a&ssp2=1&stid=9&t=tpclicked3_hc&td=1922429&tu=u1922429&u=http%3A%2F%2Fwww%2Eadmin10000%2Ecom%2Fdocument%2F6065%2Ehtml&urlid=0"   target="_blank" mpid="0" style="text-decoration:   none;"><span   style="color:#0000ff;font-size:14px;width:auto;height:auto;float:none;">java</span></a></span>.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]);  }