1. 字符串有整型的相互转换
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<strong>Stringa=String.valueOf(2); //integer to numeric string
inti=Integer.parseInt(a);//numeric string to an int </strong>
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2. 向文件末尾添加内容
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<strong>BufferedWriter out=null;
try{
out=newBufferedWriter(newFileWriter(”filename”,true));
out.write(”aString”);
}catch(IOExceptione){
// error processing code
}finally{
if(out!=null){
out.close();
}
}</strong>
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3. 得到当前方法的名字
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<strong>StringmethodName=Thread.currentThread().getStackTrace()[1].getMethodName(); </strong>
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4. 转字符串到日期
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<strong>java.util.Date=java.text.DateFormat.getDateInstance().parse(date String); </strong>
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或者是：
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<strong>SimpleDateFormat format=newSimpleDateFormat("dd.MM.yyyy");
Date date=format.parse(myString); </strong>
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5. 使用JDBC链接Oracle
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<strong>publicclassOracleJdbcTest
{
StringdriverClass="oracle.jdbc.driver.OracleDriver";
Connection con;
publicvoidinit(FileInputStream fs)throwsClassNotFoundException,SQLException,FileNotFoundException,IOException
{
Properties props=newProperties();
props.load(fs);
Stringurl=props.getProperty("db.url");
StringuserName=props.getProperty("db.user");
Stringpassword=props.getProperty("db.password");
Class.forName(driverClass);
con=DriverManager.getConnection(url,userName,password);
}
publicvoidfetch()throwsSQLException,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();
}
} </strong>
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6. 把 Java util.Date 转成 sql.Date
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<strong>java.util.Date utilDate=newjava.util.Date();
java.sql.Date sqlDate=newjava.sql.Date(utilDate.getTime());</strong>
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7. 使用NIO进行快速的文件拷贝
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<strong>publicstaticvoidfileCopy(File in,File out)
throwsIOException
{
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)
intmaxCount=(64*1024*1024)-(32*1024);
longsize=inChannel.size();
longposition=0;
while(position<size)
{
position+=inChannel.transferTo(position,maxCount,outChannel);
}
}
finally
{
if(inChannel!=null)
{
inChannel.close();
}
if(outChannel!=null)
{
outChannel.close();
}
}
} </strong>
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8. 创建图片的缩略图
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<strong>privatevoidcreateThumbnail(Stringfilename,intthumbWidth,intthumbHeight,intquality,StringoutFilename)
throwsInterruptedException,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
doublethumbRatio=(double)thumbWidth/(double)thumbHeight;
intimageWidth=image.getWidth(null);
intimageHeight=image.getHeight(null);
doubleimageRatio=(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=newBufferedImage(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=newBufferedOutputStream(newFileOutputStream(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();
} </strong>
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9.创建 JSON 格式的数据
并下面这个JAR 文件：json-rpc-1.0.jar (75 kb)
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<strong>importorg.json.JSONObject;
...
...
JSONObject json=newJSONObject();
json.put("city","Mumbai");
json.put("country","India");
...
Stringoutput=json.toString();
...</strong>
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10. 使用iText JAR生成PDF
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<strong>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;
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();
}
}
} </strong>
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11. HTTP 代理设置
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System.getProperties().put("http.proxyHost","someProxyURL");
System.getProperties().put("http.proxyPort","someProxyPort");
System.getProperties().put("http.proxyUser","someUserName");
System.getProperties().put("http.proxyPassword","somePassword");
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12. 单实例Singleton 示例
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<strong>
publicclassSimpleSingleton{
privatestaticSimpleSingleton singleInstance= newSimpleSingleton();
//Marking default constructor private
//to avoid direct instantiation.
privateSimpleSingleton(){
}
//Get instance for class SimpleSingleton
publicstaticSimpleSingleton getInstance(){
returnsingleInstance;
}
} </strong>
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另一种实现
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<strong>publicenumSimpleSingleton{
INSTANCE;
publicvoiddoSomething(){
}
}
//Call the method from Singleton:
SimpleSingleton.INSTANCE.doSomething(); </strong>
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13. 抓屏程序
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<strong>importjava.awt.Dimension;
importjava.awt.Rectangle;
importjava.awt.Robot;
importjava.awt.Toolkit;
importjava.awt.image.BufferedImage;
importjavax.imageio.ImageIO;
importjava.io.File;
...
publicvoidcaptureScreen(StringfileName)throwsException{
Dimension screenSize=Toolkit.getDefaultToolkit().getScreenSize();
Rectangle screenRectangle=newRectangle(screenSize);
Robot robot=newRobot();
BufferedImage image=robot.createScreenCapture(screenRectangle);
ImageIO.write(image,"png",newFile(fileName));
}
... </strong>
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14. 列出文件和目录
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<strong>File dir=newFile("directoryName");
String[]children=dir.list();
if(children==null){
// Either dir does not exist or is not a directory
}else{
for(inti=0;i<children.length;i++){
// Get filename of file or directory
Stringfilename=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=newFilenameFilter(){
publicbooleanaccept(File dir,Stringname){
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=newFileFilter(){
publicbooleanaccept(File file){
returnfile.isDirectory();
}
};
files=dir.listFiles(fileFilter); </strong>
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15. 创建ZIP和JAR文件
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<strong>
importjava.util.zip.*;
importjava.io.*;
publicclassZipIt{
publicstaticvoidmain(Stringargs[])throwsIOException{
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);
intbytesRead;
byte[]buffer=newbyte[1024];
CRC32 crc=newCRC32();
for(inti=1,n=args.length;i<n;i++){
Stringname=args[i];
File file=newFile(name);
if(!file.exists()){
System.err.println("Skipping: "+name);
continue;
}
BufferedInputStream bis=newBufferedInputStream(
newFileInputStream(file));
crc.reset();
while((bytesRead=bis.read(buffer))!=-1){
crc.update(buffer,0,bytesRead);
}
bis.close();
// Reset to beginning of input stream
bis=newBufferedInputStream(
newFileInputStream(file));
ZipEntry entry=newZipEntry(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();
}
} </strong>
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16. 解析/读取XML 文件
XML文件
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<?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>
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Java代码
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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(StringfileName){
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(inti=0;i<studentList.getLength();i++){
Node node=studentList.item(i);
if(node.getNodeType()==Node.ELEMENT_NODE){
System.out
.println("=====================");
Elemente=(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(Exceptione){
System.out.println(e);
}
}
publicstaticvoidmain(String[]args){
XMLParser parser=newXMLParser();
parser.getAllUserNames("c:\\test.xml");
}
}
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17. 把 Array 转换成 Map
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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"));
}
}
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18. 发送邮件
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importjavax.mail.*;
importjavax.mail.internet.*;
importjava.util.*;
publicvoidpostMail(Stringrecipients[],Stringsubject,Stringmessage,Stringfrom)throwsMessagingException
{
booleandebug=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(inti=0;i<recipients.length;i++)
{
addressTo[i]=newInternetAddress(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);
}
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19. 发送代数据的HTTP 请求
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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()));
StringstrTemp="";
while(null!=(strTemp=br.readLine())){
System.out.println(strTemp);
}
}catch(Exception ex){
ex.printStackTrace();
}
}
}
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20. 改变数组的大小
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/**
* 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(ObjectoldArray,intnewSize){
intoldSize=java.lang.reflect.Array.getLength(oldArray);
ClasselementType=oldArray.getClass().getComponentType();
ObjectnewArray=java.lang.reflect.Array.newInstance(
elementType,newSize);
intpreserveLength=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(inti=0;i<a.length;i++)
System.out.println(a[i]);
}
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是不是都是很常用的!希望大家多支持IT江湖