java常用代码有哪些

java常用代码有：1、 字符串有整型的相互转换；2、向文件末尾添加内容；3、得到当前方法的名字 ；4、转字符串到日期；5、使用JDBC链接Oracle；6、使用NIO进行快速的文件拷贝。

java常用代码有：

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

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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 
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 
9.创建 JSON 格式的数据
并下面这个JAR 文件：json-rpc-1.0.jar (75 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. 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(); 
    } 
  } 
}
11. HTTP 代理设置
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
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. 抓屏程序
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 
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 
16. 解析/读取XML 文件
XML文件
 
 
   
    John 
    B 
    12 
   
   
    Mary 
    A 
    11 
   
   
    Simon 
    A 
    18 
   
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 
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 
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
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