Common code for Java development

1. Strings have integer conversions to each other

String a = string.valueof (2);   Integer to numeric string  int i = Integer.parseint (a);//numeric string to an int

　　

2. Add content to the end of the file

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. Get the name of the current method

String methodName = Thread.CurrentThread (). Getstacktrace () [1].getmethodname ();

　　

4. Turn string to date

Java.util.Date = Java.text.DateFormat.getDateInstance (). Parse (Date String), or: SimpleDateFormat format = new SimpleDateFormat ("DD. Mm.yyyy ");  Date date = Format.parse (myString);

　　

5. Using JDBC to link 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 SYSDA    TE from dual ");       ResultSet rs = Ps.executequery ();    while (Rs.next ()) {//Does the thing you do} rs.close ();  Ps.close ();    } public static void Main (string[] args) {oraclejdbctest test = new Oraclejdbctest ();    Test.init ();  Test.fetch (); }}

　　

6. Util Java. Date turns into SQL. Date

Java.util.Date utildate = new Java.util.Date () java.sql.Date sqldate = new Java.sql.Date (Utildate.gettime ());

　　

7. Fast file copy using NiO

public static void FileCopy (file-in, file-out)      throws IOException  {    FileChannel inchannel = new Fileinputstr EAM (in). Getchannel ();    FileChannel Outchannel = new FileOutputStream (out). Getchannel ();    Try    {//     Inchannel.transferto (0, Inchannel.size (), outchannel);   Original--apparently have trouble copying large files on Windows          //magic number for Windows, 64MB-32KB)      int MaxCount = (* * 1024x768)-(* 1024x768);      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. Create a thumbnail image of a picture

private void Createthumbnail (string filename, int thumbwidth, int thumbheight, int quality, string outfilename) throws Interruptedexception, FileNotFoundException, IOException {//load image from filename image image = Toolkit.getdef    Aulttoolkit (). getImage (filename);    Mediatracker mediatracker = new Mediatracker (new Container ());    Mediatracker.addimage (image, 0);    Mediatracker.waitforid (0);       Use the this to test for errors in 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 (outFile    name));    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. Create JSON-formatted data

And the following jar file: Json-rpc-1.0.jar (KB)/http://t.cn/rz0bhua

Import Org.json.JSONObject; Jsonobject json = new Jsonobject (); Json.put ("City", "Mumbai"), Json.put ("Country", "India"); String output = json.tostring (); ....

　　

10. Generate PDF using Itext jar

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 FILEOUTPUTST Ream (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 ();}}  }

　　

HTTP proxy Settings

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. Single Instance Singleton example

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;  }}

　　

13. Screen Capture Program

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. list Files and directories

File dir = new file ("DirectoryName"); String[] Children = dir.list (); if (children = = null) {   //either dir does not exist or was 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 no return any files that start with '. '.  FilenameFilter filter = new FilenameFilter () {public   Boolean accept (File dir, String name) {     return!NAME.STARTSW ITH (".");   } }; Children = dir.list (filter);    The list of files can also be retrieved as File objects file[] files = dir.listfiles ();    This filter is returns directories FileFilter FileFilter = new FileFilter () {public   Boolean accept (file file) {     return File.isdirectory ();   } }; Files = dir.listfiles (FileFilter);

　　

15. Creating Zip and Jar files

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. Parsing/reading an XML file

XML file

<?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 code

<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 = Doc      Umentbuilderfactory.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.getno           Dename ());           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). Getnodevalu                 E ());              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. Convert Array to Map

Import Java.util.map;import org.apache.commons.lang.ArrayUtils;   public class Main {public    static void Main (string[] args) {  string[][] countries = {"states", "New York "}, {" Kingdom "," London "},     {" Netherland "," Amsterdam "}, {" Japan "," Tokyo "}, {" France "," Paris "}};
   
    map countrycapitals = arrayutils.tomap (countries);     System.out.println ("Capital of Japan" + countrycapitals.get ("Japan"));  System.out.println ("Capital of France is" + countrycapitals.get ("France"));}}
   

　　

18. Send Mail

Import Javax.mail.*;import Javax.mail.internet.*;import java.util.*; public void Postmail (string recipients[], string subject, String message, string from) throws Messagingexception {Boo      Lean 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.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 e-mail 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. HTTP request to send generation data

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. Changing the size of the array

/*** reallocates An array with a new size, and copies the contents* of the old array to the new array.* @param oldarray th e old array, to is 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 (ol Darray);  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 = {};  A = (int[]) Resizearray (a,5);  A[3] = 4;  A[4] = 5;  for (int i=0; i<a.length; i++)   System.out.println (A[i]);}

　　

21. Iterate through all the parameters and values passed over the page

Enumeration<?> en = Request.getparameternames ();        while (En.hasmoreelements ()) {            String el = en.nextelement (). toString ();          System.out.println ("| | | | |" +el+ "=" +request.getparameter (EL));        

　　

JSON resolves to list

/** * JSON parsing * @param jsonstring * @return * @throws jsonexception */public list<datavo> jsontest (String jsonstring) Throws Jsonexception{//string jsonstring= "{\" answers\ ": [{\" loginname\ ": \" zhangfan\ ", \" password\ ": \" Userpass\ "},{ \ "password\": \ "Userpass\", \ "email\": \ "[Email protected]\"}]} "; Jsonobject json= New Jsonobject (jsonstring); Jsonarray Jsonarray=json.getjsonarray ("ARR"); list<datavo> answerlist = new arraylist<datavo> (); for (int i=0;i<jsonarray.length (); i++) {JSONObject Relue= (jsonobject) jsonarray.get (i); Long id= (long) relue.get ("id"); String val = (string) relue.get ("Val");D atavo datavo = new Datavo ();d Atavo.setid (ID);d Atavo.setval (val); Answerlist.add (Datavo);} return answerlist;}

　　

　　

Common code for Java development