常用java代码
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1，字符串有整型的相互转换
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<strong>String a = String.valueOf(2); //integer to numeric string
int i = Integer.parseInt(a); //numeric string to an int </strong>
2，向文件末尾添加内容
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<strong>BufferedWriterout=null;
try{
out=newBufferedWriter(newFileWriter(”filename”,true));
out.write(”aString”);
}catch(IOExceptione){
// error processing code
}finally{
if(out!=null){
out.close();
}
}</strong>
3，得到当前方法的名字
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<strong>String methodName = Thread.currentThread().getStackTrace()[1].getMethodName(); </strong>
4，转字符串到日期
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<strong>java.util.Date=java.text.DateFormat.getDateInstance().parse(dateString); </strong>
或者是：
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<strong>SimpleDateFormat format = new SimpleDateFormat( "dd.MM.yyyy" );
Date date = format.parse( myString ); </strong>
5，使用JDBC的链接甲骨文
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<strong>publicclassOracleJdbcTest
{
StringdriverClass="oracle.jdbc.driver.OracleDriver";
Connectioncon;
publicvoidinit(FileInputStreamfs)throwsClassNotFoundException,SQLException,FileNotFoundException,IOException
{
Propertiesprops=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
{
PreparedStatementps=con.prepareStatement("select SYSDATE from dual");
ResultSetrs=ps.executeQuery();
while(rs.next())
{
// do the thing you do
}
rs.close();
ps.close();
}
publicstaticvoidmain(String[]args)
{
OracleJdbcTesttest=newOracleJdbcTest();
test.init();
test.fetch();
}
} </strong>
6，把Java的util.Date转成sql.Date
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<strong>java.util.Date utilDate = new java.util.Date();
java.sql.Date sqlDate = new java.sql.Date(utilDate.getTime());</strong>
7，使用NIO进行快速的文件拷贝
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<strong>publicstaticvoidfileCopy(Filein,Fileout)
throwsIOException
{
FileChannelinChannel=newFileInputStream(in).getChannel();
FileChanneloutChannel=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>
8，创建图片的缩略图
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<strong>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();
} </strong>
9。创建JSON格式的数据
并下面这个JAR文件：JSON-RPC-1.0.jar的（75 KB）
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<strong>importorg.json.JSONObject;
...
...
JSONObjectjson=newJSONObject();
json.put("city","Mumbai");
json.put("country","India");
...
Stringoutput=json.toString();
...</strong>
10。使用iText的JAR生成PDF格式
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<strong>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();
}
}
} </strong>
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");
12，单实例单例示例
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<strong>
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;
}
} </strong>
另一种实现
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<strong>publicenumSimpleSingleton{
INSTANCE;
publicvoiddoSomething(){
}
}
//Call the method from Singleton:
SimpleSingleton.INSTANCE.doSomething(); </strong>
13，抓屏程序
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<strong>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));
}
... </strong>
14，列出文件和目录
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<strong>Filedir=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 `.'.
FilenameFilterfilter=newFilenameFilter(){
publicbooleanaccept(Filedir,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
FileFilterfileFilter=newFileFilter(){
publicbooleanaccept(Filefile){
returnfile.isDirectory();
}
};
files=dir.listFiles(fileFilter); </strong>
15，创建ZIP和JAR文件
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<strong>
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();
}
} </strong>
16。解析/读取XML文件
XML文件
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<?xmlversion="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>
的Java代码
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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，把数组转换成地图
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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"}};
MapcountryCapitals=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
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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
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importjava.io.BufferedReader;
importjava.io.InputStreamReader;
importjava.net.URL;
publicclassMain{
publicstaticvoidmain(String[]args) {
try{
URLmy_url=newURL("http://coolshell.cn/");
BufferedReaderbr=newBufferedReader(newInputStreamReader(my_url.openStream()));
StringstrTemp="";
while(null!=(strTemp=br.readLine())){
System.out.println(strTemp);
}
}catch(Exceptionex){
ex.printStackTrace();
}
}
}
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]);
}
是不是都是很常用的！希望大家多支持的IT江湖
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