20个非常有用的Java程序片段
先收藏了，以后应该用的到。
下面是20个非常有用的Java程序片段，希望能对你有用。
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
2. 向文件末尾添加内容
BufferedWriter out=null;try{out=newBufferedWriter(newFileWriter(”filename”,true));out.write(”aString”);}catch(IOExceptione){// 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=newSimpleDateFormat("dd.MM.yyyy");Date date=format.parse(myString);
5. 使用JDBC链接Oracle
publicclassOracleJdbcTest{String driverClass="oracle.jdbc.driver.OracleDriver";Connection con;publicvoidinit(FileInputStream fs)throws ClassNotFoundException,SQLException,FileNotFoundException,IOException{Properties props=newProperties();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);}publicvoidfetch()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();}publicstaticvoidmain(String[]args){OracleJdbcTest test=newOracleJdbcTest();test.init();test.fetch();}}
6. 把 Java util.Date 转成 sql.Date
java.util.Date utilDate=newjava.util.Date();java.sql.Date sqlDate=newjava.sql.Date(utilDate.getTime());
7. 使用NIO进行快速的文件拷贝
publicstaticvoidfileCopy(Filein,File out)throws IOException{FileChannel inChannel=newFileInputStream(in).getChannel();FileChannel outChannel=newFileOutputStream(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
privatevoidcreateThumbnail(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=newMediaTracker(newContainer());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
请先阅读这篇文章了解一些细节，
并下面这个JAR 文件：json-rpc-1.0.jar (75 kb)
importorg.json.JSONObject;......JSONObject json=newJSONObject();json.put("city","Mumbai");json.put("country","India");...String output=json.toString();...
10. 使用iText JAR生成PDF
阅读这篇文章了解更多细节
importjava.io.File;importjava.io.FileOutputStream;importjava.io.OutputStream;importjava.util.Date;importcom.lowagie.text.Document;importcom.lowagie.text.Paragraph;importcom.lowagie.text.pdf.PdfWriter;/**
* Java学习交流QQ群：589809992 我们一起学Java！
*/publicclassGeneratePDF{publicstaticvoidmain(String[]args){try{OutputStream file=newFileOutputStream(newFile("C:\\Test.pdf"));Document document=newDocument();PdfWriter.getInstance(document,file);document.open();document.add(newParagraph("Hello Kiran"));document.add(newParagraph(newDate().toString()));document.close();file.close();}catch(Exceptione){e.printStackTrace();}}}
11. HTTP 代理设置
阅读这篇文章了解更多细节。
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
请先阅读这篇文章了解更多信息
publicclassSimpleSingleton{privatestaticSimpleSingleton singleInstance=newSimpleSingleton();//Marking default constructor private //to avoid direct instantiation. privateSimpleSingleton(){}//Get instance for class SimpleSingleton publicstaticSimpleSingletongetInstance(){returnsingleInstance;}}
另一种实现
publicenumSimpleSingleton{INSTANCE;publicvoiddoSomething(){}}//Call the method from Singleton: SimpleSingleton.INSTANCE.doSomething();
13. 抓屏程序
阅读这篇文章获得更多信息。
importjava.awt.Dimension;importjava.awt.Rectangle;importjava.awt.Robot;importjava.awt.Toolkit;importjava.awt.image.BufferedImage;importjavax.imageio.ImageIO;importjava.io.File;...publicvoidcaptureScreen(String fileName)throws Exception{Dimension screenSize=Toolkit.getDefaultToolkit().getScreenSize();Rectangle screenRectangle=newRectangle(screenSize);Robot robot=newRobot();BufferedImage image=robot.createScreenCapture(screenRectangle);ImageIO.write(image,"png",newFile(fileName));}...
14. 列出文件和目录
File dir=newFile("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
importjava.util.zip.*;importjava.io.*;/**
* Java学习交流QQ群：589809992 我们一起学Java！
*/publicclassZipIt{publicstaticvoidmain(String args[])throws IOException{if(args.length<2){System.err.println("usage: java ZipIt Zip.zip file1 file2 file3");System.exit(-1);}File zipFile=newFile(args[0]);if(zipFile.exists()){System.err.println("Zip file already exists, please try another");System.exit(-2);}FileOutputStream fos=newFileOutputStream(zipFile);ZipOutputStream zos=newZipOutputStream(fos);int bytesRead;byte[]buffer=newbyte[1024];CRC32 crc=newCRC32();for(int i=1,n=args.length;i
16. 解析/读取XML 文件
XML文件
JohnB12MaryA11SimonA18
Java代码
packagenet.viralpatel.java.xmlparser;importjava.io.File;importjavax.xml.parsers.DocumentBuilder;importjavax.xml.parsers.DocumentBuilderFactory;importorg.w3c.dom.Document;importorg.w3c.dom.Element;importorg.w3c.dom.Node;importorg.w3c.dom.NodeList;publicclassXMLParser{publicvoidgetAllUserNames(String fileName){try{DocumentBuilderFactory dbf=DocumentBuilderFactory.newInstance();DocumentBuilder db=dbf.newDocumentBuilder();File file=newFile(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
importjava.util.Map;importorg.apache.commons.lang.ArrayUtils;publicclassMain{publicstaticvoidmain(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
importjavax.mail.*;importjavax.mail.internet.*;importjava.util.*;publicvoidpostMail(String recipients[],String subject,String message,Stringfrom)throws MessagingException{boolean debug=false;//Set the host smtp address Properties props=newProperties();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=newMimeMessage(session);// set the from and to address InternetAddress addressFrom=newInternetAddress(from);msg.setFrom(addressFrom);InternetAddress[]addressTo=newInternetAddress[recipients.length];for(int i=0;i
19. 发送代数据的HTTP 请求
importjava.io.BufferedReader;importjava.io.InputStreamReader;importjava.net.URL;publicclassMain{publicstaticvoidmain(String[]args){try{URL my_url=newURL("http://coolshell.cn/");BufferedReader br=newBufferedReader(newInputStreamReader(my_url.openStream()));String strTemp="";while(null!=(strTemp=br.readLine())){System.out.println(strTemp);}}catch(Exceptionex){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.
*/privatestaticObjectresizeArray(Object oldArray,int newSize){int oldSize=java.lang.reflect.Array.getLength(oldArray);ClasselementType=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);returnnewArray;}// Test routine for resizeArray(). publicstaticvoidmain(String[]args){int[]a={1,2,3};a=(int[])resizeArray(a,5);a[3]=4;a[4]=5;for(int i=0;i
