java常用代码有哪些

String a = String.valueOf2);   //integer to numeric string  
int i = Integer.parseInta); //numeric string to an int

BufferedWriter out = null; 
try { 
  out = new BufferedWriternew FileWriter”filename”, true)); 
  out.write”aString”); 
} catch IOException e) { 
  // error processing code 
} finally { 
  if out != null) { 
    out.close); 
  } 
}

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

java.util.Date = java.text.DateFormat.getDateInstance).parsedate String);
//或者是：
SimpleDateFormat format = new SimpleDateFormat "dd.MM.yyyy" );  
Date date = format.parse myString );

public class OracleJdbcTest 
{ 
  String driverClass = "oracle.jdbc.driver.OracleDriver"; 
  
  Connection con; 
  
  public void initFileInputStream fs) throws ClassNotFoundException, SQLException, FileNotFoundException, IOException 
  { 
    Properties props = new Properties); 
    props.loadfs); 
    String url = props.getProperty"db.url"); 
    String userName = props.getProperty"db.user"); 
    String password = props.getProperty"db.password"); 
    Class.forNamedriverClass); 
  
    con=DriverManager.getConnectionurl, 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 mainString[] args) 
  { 
    OracleJdbcTest test = new OracleJdbcTest); 
    test.init); 
    test.fetch); 
  } 
}

java.util.Date utilDate = new java.util.Date); 
java.sql.Date sqlDate = new java.sql.DateutilDate.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.transferTo0, 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 createThumbnailString filename, int thumbWidth, int thumbHeight, int quality, String outFilename) 
    throws InterruptedException, FileNotFoundException, IOException 
  { 
    // load image from filename 
    Image image = Toolkit.getDefaultToolkit).getImagefilename); 
    MediaTracker mediaTracker = new MediaTrackernew Container)); 
    mediaTracker.addImageimage, 0); 
    mediaTracker.waitForID0); 
    // use this to test for errors at this point: System.out.printlnmediaTracker.isErrorAny)); 
  
    // determine thumbnail size from WIDTH and HEIGHT 
    double thumbRatio = double)thumbWidth / double)thumbHeight; 
    int imageWidth = image.getWidthnull); 
    int imageHeight = image.getHeightnull); 
    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 BufferedImagethumbWidth, thumbHeight, BufferedImage.TYPE_INT_RGB); 
    Graphics2D graphics2D = thumbImage.createGraphics); 
    graphics2D.setRenderingHintRenderingHints.KEY_INTERPOLATION, RenderingHints.VALUE_INTERPOLATION_BILINEAR); 
    graphics2D.drawImageimage, 0, 0, thumbWidth, thumbHeight, null); 
  
    // save thumbnail image to outFilename 
    BufferedOutputStream out = new BufferedOutputStreamnew FileOutputStreamoutFilename)); 
    JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoderout); 
    JPEGEncodeParam param = encoder.getDefaultJPEGEncodeParamthumbImage); 
    quality = Math.max0, Math.minquality, 100)); 
    param.setQualityfloat)quality / 100.0f, false); 
    encoder.setJPEGEncodeParamparam); 
    encoder.encodethumbImage); 
    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 mainString[] args) { 
    try { 
      OutputStream file = new FileOutputStreamnew File"C:\\Test.pdf")); 
  
      Document document = new Document); 
      PdfWriter.getInstancedocument, file); 
      document.open); 
      document.addnew Paragraph"Hello Kiran")); 
      document.addnew Paragraphnew 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 captureScreenString fileName) throws Exception { 
  
  Dimension screenSize = Toolkit.getDefaultToolkit).getScreenSize); 
  Rectangle screenRectangle = new RectanglescreenSize); 
  Robot robot = new Robot); 
  BufferedImage image = robot.createScreenCapturescreenRectangle); 
  ImageIO.writeimage, "png", new FilefileName)); 
  
} 
...

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 acceptFile dir, String name) { 
     return !name.startsWith"."); 
   } 
 }; 
 children = dir.listfilter); 
  
 // 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 acceptFile file) { 
     return file.isDirectory); 
   } 
 }; 
 files = dir.listFilesfileFilter);

import java.util.zip.*; 
import java.io.*; 
  
public class ZipIt { 
  public static void mainString args[]) throws IOException { 
    if args.length < 2) { 
      System.err.println"usage: java ZipIt Zip.zip file1 file2 file3"); 
      System.exit-1); 
    } 
    File zipFile = new Fileargs[0]); 
    if zipFile.exists)) { 
      System.err.println"Zip file already exists, please try another"); 
      System.exit-2); 
    } 
    FileOutputStream fos = new FileOutputStreamzipFile); 
    ZipOutputStream zos = new ZipOutputStreamfos); 
    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 Filename); 
      if !file.exists)) { 
        System.err.println"Skipping: " + name); 
        continue; 
      } 
      BufferedInputStream bis = new BufferedInputStream 
        new FileInputStreamfile)); 
      crc.reset); 
      while bytesRead = bis.readbuffer)) != -1) { 
        crc.updatebuffer, 0, bytesRead); 
      } 
      bis.close); 
      // Reset to beginning of input stream 
      bis = new BufferedInputStream 
        new FileInputStreamfile)); 
      ZipEntry entry = new ZipEntryname); 
      entry.setMethodZipEntry.STORED); 
      entry.setCompressedSizefile.length)); 
      entry.setSizefile.length)); 
      entry.setCrccrc.getValue)); 
      zos.putNextEntryentry); 
      while bytesRead = bis.readbuffer)) != -1) { 
        zos.writebuffer, 0, bytesRead); 
      } 
      bis.close); 
    } 
    zos.close); 
  } 
}

<?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 getAllUserNamesString fileName) { 
    try { 
      DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance); 
      DocumentBuilder db = dbf.newDocumentBuilder); 
      File file = new FilefileName); 
      if file.exists)) { 
        Document doc = db.parsefile); 
        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.itemi); 
  
            if node.getNodeType) == Node.ELEMENT_NODE) { 
  
              System.out 
                  .println"====================="); 
  
              Element e = Element) node; 
              NodeList nodeList = e.getElementsByTagName"name"); 
              System.out.println"Name: "
                  + nodeList.item0).getChildNodes).item0) 
                      .getNodeValue)); 
  
              nodeList = e.getElementsByTagName"grade"); 
              System.out.println"Grade: "
                  + nodeList.item0).getChildNodes).item0) 
                      .getNodeValue)); 
  
              nodeList = e.getElementsByTagName"age"); 
              System.out.println"Age: "
                  + nodeList.item0).getChildNodes).item0) 
                      .getNodeValue)); 
            } 
          } 
        } else { 
          System.exit1); 
        } 
      } 
    } catch Exception e) { 
      System.out.printlne); 
    } 
  } 
  public static void mainString[] 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 mainString[] args) { 
  String[][] countries = { { "United States", "New York" }, { "United Kingdom", "London" }, 
    { "Netherland", "Amsterdam" }, { "Japan", "Tokyo" }, { "France", "Paris" } }; 
  
  Map countryCapitals = ArrayUtils.toMapcountries); 
  
  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.getDefaultInstanceprops, null); 
  session.setDebugdebug); 
  
  // create a message 
  Message msg = new MimeMessagesession); 
  
  // set the from and to address 
  InternetAddress addressFrom = new InternetAddressfrom); 
  msg.setFromaddressFrom); 
  
  InternetAddress[] addressTo = new InternetAddress[recipients.length]; 
  for int i = 0; i < recipients.length; i++) 
  { 
    addressTo[i] = new InternetAddressrecipients[i]); 
  } 
  msg.setRecipientsMessage.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.setSubjectsubject); 
  msg.setContentmessage, "text/plain"); 
  Transport.sendmsg); 
}

import java.io.BufferedReader; 
import java.io.InputStreamReader; 
import java.net.URL; 
  
public class Main { 
  public static void mainString[] args) { 
    try { 
      URL my_url = new URL"http://coolshell.cn/"); 
      BufferedReader br = new BufferedReadernew InputStreamReadermy_url.openStream))); 
      String strTemp = ""; 
      whilenull != strTemp = br.readLine))){ 
      System.out.printlnstrTemp); 
    } 
    } catch Exception ex) { 
      ex.printStackTrace); 
    } 
  } 
}

/** 
* 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.getLengtholdArray); 
  Class elementType = oldArray.getClass).getComponentType); 
  Object newArray = java.lang.reflect.Array.newInstance 
     elementType,newSize); 
  int preserveLength = Math.minoldSize,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[])resizeArraya,5); 
  a[3] = 4; 
  a[4] = 5; 
  for int i=0; i<a.length; i++) 
   System.out.println a[i]); 
}