1蝙昙、字符串有整型的相互轉(zhuǎn)換
String a = String.valueOf(2);??//integer to numeric string??
int i = Integer.parseInt(a); //numeric string to an int
2闪萄、向文件末尾添加內(nèi)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、得到當(dāng)前方法的名字
String methodName = Thread.currentThread().getStackTrace()[1].getMethodName();
4奇颠、轉(zhuǎn)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败去、使用JDBC鏈接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 轉(zhuǎn)成 sql.Date
java.util.Date utilDate = new java.util.Date();??
java.sql.Date sqlDate = new java.sql.Date(utilDate.getTime());
7烈拒、使用NIO進(jìn)行快速的文件拷貝
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 < size )??
??????{??
????????position += inChannel.transferTo( position, maxCount, outChannel );??
??????}??
????}??
????finally?
????{??
??????if ( inChannel != null )??
??????{??
????????inChannel.close();??
??????}??
??????if ( outChannel != null )??
??????{??
????????outChannel.close();??
??????}??
????}??
??}
8圆裕、創(chuàng)建圖片的縮略圖
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、創(chuàng)建 JSON 格式的數(shù)據(jù)
import org.json.JSONObject;??
...??
...??
JSONObject json = new JSONObject();??
json.put("city", "Mumbai");??
json.put("country", "India");??
...??
String output = json.toString();??
...
10荆几、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吓妆、HTTP 代理設(shè)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、單實例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;??
??}??
}
另一種實現(xiàn)
public enum SimpleSingleton {??
??INSTANCE;??
??public void doSomething() {??
??}??
}??
//Call the method from Singleton:??
SimpleSingleton.INSTANCE.doSomething();
13吨铸、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行拢、列出文件和目錄
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、創(chuàng)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/讀取XML 文件
XML文件
????John?
????B?
????12?
????Mary?
????A?
????11?
????Simon?
????A?
????18?
Java代碼
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 轉(zhuǎn)換成 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. 發(fā)送郵件
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. 發(fā)送代數(shù)據(jù)的HTTP 請求
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. 改變數(shù)組的大小
/**
* 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<a.length; i++)?
??????System.out.println (a[i]);?
}
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