Java开发常用代码

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();
  }
}

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();
  }
}

java.util.Date utilDate = new java.util.Date();
java.sql.Date sqlDate = new java.sql.Date(utilDate.getTime());

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();
      }
    }
  }

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();
  }

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

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();
    }
  }
}

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

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;
  }
}

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));
   
}
...

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);

<?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>

<span style="font-family:Arial;font-size:14px;">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");
  }
}

import java.util.Map;
import org.apache.commons.lang.ArrayUtils;
   
public class Main {
   
 public static void main(String[] args) {
  String[][] countries = { { "United States", "New York" }, { "United Kingdom", "London" }, 
    { "Netherland", "Amsterdam" }, { "Japan", "Tokyo" }, { "France", "Paris" } };
   
  Map countryCapitals = ArrayUtils.toMap(countries);
   
  System.out.println("Capital of Japan is " + countryCapitals.get("Japan"));
  System.out.println("Capital of France is " + countryCapitals.get("France"));
 }
}

import javax.mail.*;
import javax.mail.internet.*;
import java.util.*;
   
public void postMail( String recipients[ ], String subject, String message , String from) throws MessagingException 
{
  boolean debug = false;
   
   //Set the host smtp address
   Properties props = new Properties();
   props.put("mail.smtp.host", "smtp.example.com");
   
  // create some properties and get the default Session
  Session session = Session.getDefaultInstance(props, null);
  session.setDebug(debug);
   
  // create a message
  Message msg = new MimeMessage(session);
   
  // set the from and to address
  InternetAddress addressFrom = new InternetAddress(from);
  msg.setFrom(addressFrom);
   
  InternetAddress[] addressTo = new InternetAddress[recipients.length];
  for (int i = 0; i < recipients.length; i++)
  {
    addressTo[i] = new InternetAddress(recipients[i]);
  }
  msg.setRecipients(Message.RecipientType.TO, addressTo);
   
  // Optional : You can also set your custom headers in the Email if you Want
  msg.addHeader("MyHeaderName", "myHeaderValue");
   
  // Setting the Subject and Content Type
  msg.setSubject(subject);
  msg.setContent(message, "text/plain");
  Transport.send(msg);
}

import 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();
    }
  }
}