- 当前位置：首页 >IT科技类资讯 >程序员花2小时总结：20个非常有用的Java程序片段
程序员花2小时总结：20个非常有用的Java程序片段
发布时间：2025-11-05 05:30:02 来源：创站工坊 作者：人工智能
下面是程序常有程序20个非常有用的Java程序片段，希望能对你有用。员花用
1、总结字符串有整型的个非相互转换
1.String a = String.valueOf(2); //integer to numeric string 2.int i = Integer.parseInt(a); //numeric string to an int
2.向文件末尾添加内容
1.BufferedWriter out = null; 2.try { 3 out = new BufferedWriter(new FileWriter(”filename”, true)); 4 out.write(”aString”); 5} catch (IOException e) { 6 // error processing code 7} finally { 8 if (out != null) { 9 out.close(); 10 } 11}3.得到当前方法的名字
1.String methodName = Thread.currentThread().getStackTrace()[1].getMethodName();4.转字符串到日期
1.java.util.Date = java.text.DateFormat.getDateInstance().parse(date String);或者是云服务器：
1.SimpleDateFormat format = new SimpleDateFormat( "dd.MM.yyyy" ); 2.Date date = format.parse( myString );5.使用JDBC链接Oracle
1.public class OracleJdbcTest 2.{ 3 String driverClass = "oracle.jdbc.driver.OracleDriver"; 45 Connection con; 67 public void init(FileInputStream fs) throws ClassNotFoundException, SQLException, FileNotFoundException, IOException 8 { 9 Properties props = new Properties(); 10 props.load(fs); 11 String url = props.getProperty("db.url"); 12 String userName = props.getProperty("db.user"); 13 String password = props.getProperty("db.password"); 14 Class.forName(driverClass); 1516 con=DriverManager.getConnection(url, userName, password); 17 } 1819 public void fetch() throws SQLException, IOException 20 { 21 PreparedStatement ps = con.prepareStatement("select SYSDATE from dual"); 22 ResultSet rs = ps.executeQuery(); 2324 while (rs.next()) 25 { 26 // do the thing you do 27 } 28 rs.close(); 29 ps.close(); 30 } 3132 public static void main(String[] args) 33 { 34 OracleJdbcTest test = new OracleJdbcTest(); 35 test.init(); 36 test.fetch(); 37 } 38}6.把 Java util.Date 转成 sql.Date
1.java.util.Date utilDate = new java.util.Date(); 2.java.sql.Date sqlDate = new java.sql.Date(utilDate.getTime());7.使用NIO进行快速的文件拷贝
1.public static void fileCopy( File in, File out ) 2. throws IOException 3. { 4. FileChannel inChannel = new FileInputStream( in ).getChannel(); 5. FileChannel outChannel = new FileOutputStream( out ).getChannel(); 6. try7. { 8.// inChannel.transferTo(0, inChannel.size(), outChannel); // original -- apparently has trouble copying large files on Windows 9.10. // magic number for Windows, 64Mb - 32Kb) 11. int maxCount = (64 * 1024 * 1024) - (32 * 1024); 12. long size = inChannel.size(); 13. long position = 0; 14. while ( position < size ) 15. { 16. position += inChannel.transferTo( position, maxCount, outChannel ); 17. } 18. } 19. finally20. { 21. if ( inChannel != null ) 22. { 23. inChannel.close(); 24. } 25. if ( outChannel != null ) 26. { 27. outChannel.close(); 28. } 29. } 30. }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 < 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(); }9.创建 JSON 格式的数据
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; } }另一种实现
public enum SimpleSingleton { INSTANCE; public void doSomething() { } } //Call the method from Singleton: SimpleSingleton.INSTANCE.doSomething();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 < 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);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 < 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.解析/读取XML 文件
XML文件
<?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 < 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"); } }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 < 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); }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 contentsof 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<a.length; i++) System.out.println (a[i]); }阿里Java高级大牛直播讲解知识点，分享知识，b2b信息网片段上面几大专题都是程序常有程序各位老师多年工作经验的梳理和总结，带着大家全面、员花用科学地建立自己的总结技术体系和技术认知！
个非香港云服务器源码库香港云服务器源码下载亿华云IT资讯网益华科技服务器租用IT技术网企商汇极客码头创站工坊亿华科技科技前瞻益强编程舍益强智囊团亿华灵动亿华智慧云全栈开发益强IT技术网益强前沿资讯思维库益强智未来亿华互联亿华智造亿华云计算多维IT资讯益强编程堂益华科技极客编程益强科技益强资讯优选编程之道码上建站汇智坊IT资讯网益华IT技术论坛云智核益强数据堂益强科技亿华云码力社益华科技智能时代云站无忧技术快报
- Copyright © 2025 Powered by 程序员花2小时总结：20个非常有用的Java程序片段,创站工坊 滇ICP备2023006006号-44sitemap