常用Java程序片段

1、改变数组的大小

package com.js.ai.modules.jsa.test;

public class Testxf {
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;
}
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.print (a[i]+";");
}
}

　2、发送代数据的HTTP 请求

package com.js.ai.modules.jsa.test;

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.net.URL;
public class Testxf {
public static void main(String[] args) {
	try {
		URL my_url=new URL("https://open.alipay.com/platform/home.htm");
		BufferedReader br=new BufferedReader(new InputStreamReader(my_url.openStream()));
		 String strTemp = "";
		 while(null!=(strTemp=br.readLine())){
			 System.out.println(strTemp);
		 }
	} catch (Exception e) {
		e.printStackTrace();
	}
}
}

3、发送邮件

package com.js.ai.modules.jsa.test;

import java.util.Properties;

import javax.mail.Message;
import javax.mail.MessagingException;
import javax.mail.Session;
import javax.mail.Transport;
import javax.mail.internet.InternetAddress;
import javax.mail.internet.MimeMessage;

public class Testxf {
	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);
	}
}

4、把 Array 转换成 Map

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"));
  }

5、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：
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");
    }
}

6、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);

7、抓屏程序

package com.js.ai.modules.jsa.test;

import java.awt.Dimension;
import java.awt.Rectangle;
import java.awt.Robot;
import java.awt.Toolkit;
import java.awt.image.BufferedImage;
import java.io.File;

import javax.imageio.ImageIO;

public class Testxf {
	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));    

		}
	public static void main(String[] args) throws Exception {
		Testxf testxf =new Testxf();
		testxf.captureScreen("C:/Users/Administrator/Desktop/JSAxfz/captureScreen.png");
	}
}

8、使用iText JAR生成PDF

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();
        }
    }
}

9、使用NIO进行快速的文件拷贝

package com.js.ai.modules.jsa.test;
import java.awt.Container;
import java.awt.Graphics2D;
import java.awt.Image;
import java.awt.MediaTracker;
import java.awt.RenderingHints;
import java.awt.Toolkit;
import java.awt.image.BufferedImage;
import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.nio.channels.FileChannel;

import javax.imageio.ImageIO;
public class Testxf {
	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();
            }
        }
    }
	public static void main(String[] args) throws IOException {
		Testxf testxf =new Testxf();
		File in=new File("C:/Users/Administrator/Desktop/JSAxfz/yuan.txt");
		File out=new File("C:/Users/Administrator/Desktop/JSAxfz/copy.txt");
		testxf.fileCopy(in, out);
	}
}

10、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();
    }
}