20个非常有用的Java程序片段

下面是20个非常有用的Java程序片段,希望能对你有用。

java培训-20个非常有用的Java程序片段,培训-20java片段

                                                                          
java培训-20个非常有用的Java程序片段

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

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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

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

  4. 转字符串到日期

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<span id="12_nwp">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">= java.text.DateFormat.getDateInstance().parse(date String);

  或者是:

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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">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">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">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">= (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">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">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">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">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">_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">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"  >_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="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"> 

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">    } 

}

  17. 把 Array 转换成 Map 

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import <span id="3_nwp">_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">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">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">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">_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">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">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">   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]); 

}

java培训-20个非常有用的Java程序片段
下面是20个非常有用的Java程序片段,希望能对你有…

1. 字符串有整型的相互转换

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

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

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

4. 转字符串到日期

java.util.Date = java.text.DateFormat.getDateInstance().parse(date String);

或者是:

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

5. 使用JDBC链接Oracle

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

java.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

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

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();  
    }

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)

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

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. HTTP 代理设置

阅读这篇 文章 了解更多细节。

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

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

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。

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. 列出文件和目录

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

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();  
    }  
}

16. 解析/读取XML 文件

XML文件

<?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

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. 把 Array 转换成 Map 

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. 发送邮件

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. 发送代数据的HTTP 请求

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();  
        }  
    }  
}

20. 改变数组的大小

/** 
* 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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