- 字符串有整型的相互转换
Java
String a = String.valueOf(2); //integer to numeric string
int i = Integer.parseInt(a); //numeric string to an int
1
2
Stringa=String.valueOf(2); //integer to numeric string
inti=Integer.parseInt(a);//numeric string to an int
向文件末尾添加内容
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();}
}
BufferedWriter out=null;
try{
out=newBufferedWriter(newFileWriter(”filename”,true));
}catch(IOExceptione){
}finally{
if(out!=null){
//代码效果参考：http://0791zd.com/bx/art_7285.html得到当前方法的名字
String methodName = Thread.currentThread().getStackTrace()[1].getMethodName();
StringmethodName=Thread.currentThread().getStackTrace()[1].getMethodName();- 转字符串到日期
java.util.Date = java.text.DateFormat.getDateInstance().parse(date String);
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 );
SimpleDateFormat format=newSimpleDateFormat("dd.MM.yyyy");
Date date=format.parse(myString); 使用JDBC链接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();}
publicclassOracleJdbcTest
StringdriverClass="oracle.jdbc.driver.OracleDriver";
publicvoidinit(FileInputStream fs)throwsClassNotFoundException,SQLException,FileNotFoundException,IOExceptionProperties props=newProperties(); Stringurl=props.getProperty("db.url"); StringuserName=props.getProperty("db.user"); Stringpassword=props.getProperty("db.password"); con=DriverManager.getConnection(url,userName,password);publicvoidfetch()throwsSQLException,IOException
PreparedStatement ps=con.prepareStatement("select SYSDATE from dual"); ResultSet rs=ps.executeQuery(); while(rs.next())publicstaticvoidmain(String[]args)
OracleJdbcTest test=newOracleJdbcTest();- 把 Java util.Date 转成 sql.Date
java.util.Date utilDate = new java.util.Date();
java.sql.Date sqlDate = new java.sql.Date(utilDate.getTime());
java.util.Date utilDate=newjava.util.Date();
java.sql.Date sqlDate=newjava.sql.Date(utilDate.getTime()); - 使用NIO进行快速的文件拷贝
public
static void fileCopy( File in, File out )
).getChannel();throws IOException FileChannel inChannel = new FileInputStream( in
// inChannel.transferTo(0, inChannel.size(), outChannel);FileChannel outChannel = new FileOutputStream( out try
// original -- apparently has trouble copying large files on Windows
outChannel );// 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,
}} finally if ( inChannel != null ) inChannel.close(); if ( outChannel != null ) outChannel.close();
publicstaticvoidfileCopy(File in,File out)
// inChannel.transferTo(0, inChannel.size(), outChannel); // original -- apparently has trouble copying large files on WindowsthrowsIOException FileChannel inChannel=newFileInputStream(in).getChannel(); FileChannel outChannel=newFileOutputStream(out).getChannel();intmaxCount=(64*1024*1024)-(32*1024); longsize=inChannel.size(); longposition=0; while(position<size) position+=inChannel.transferTo(position,maxCount,outChannel); if(inChannel!=null) if(outChannel!=null) - 创建图片的缩略图
private void createThumbnail(String filename, int thumbWidth, int thumbHeight, int quality, String outFilename)
privatevoidcreateThumbnail(Stringfilename,intthumbWidth,intthumbHeight,intquality,StringoutFilename)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);
9.创建 JSON 格式的数据throwsInterruptedException,FileNotFoundException,IOException Image image=Toolkit.getDefaultToolkit().getImage(filename); MediaTracker mediaTracker=newMediaTracker(newContainer()); mediaTracker.addImage(image,0); 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); 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); 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);
并下面这个JAR 文件：json-rpc-1.0.jar (75 kb)
import org.json.JSONObject;
...
JSONObject json = new JSONObject();
json.put("city", "Mumbai");
json.put("country", "India");
String output = json.toString();
...
importorg.json.JSONObject;
JSONObject json=newJSONObject();
json.put("city","Mumbai");
json.put("country","India");
Stringoutput=json.toString();
... - 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) {
importjava.io.File;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();
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.add(newParagraph("Hello Kiran")); document.add(newParagraph(newDate().toString())); }catch(Exceptione){ - 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");
System.getProperties().put("http.proxyHost","someProxyURL");
System.getProperties().put("http.proxyPort","someProxyPort");
System.getProperties().put("http.proxyUser","someUserName");
System.getProperties().put("http.proxyPassword","somePassword"); - 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() {
publicclassSimpleSingleton{return singleInstance;
privatestaticSimpleSingleton singleInstance= newSimpleSingleton();
privateSimpleSingleton(){
publicstaticSimpleSingleton getInstance(){
另一种实现returnsingleInstance;
public enum SimpleSingleton {
INSTANCE;
public void doSomething() {
}
//Call the method from Singleton:
SimpleSingleton.INSTANCE.doSomething();
publicenumSimpleSingleton{
publicvoiddoSomething(){ - 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));
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)); - 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) {
files = dir.listFiles(fileFilter);return file.isDirectory();
File dir=newFile("directoryName");
String[]children=dir.list();
if(children==null){
}else{
for(inti=0;i<children.length;i++){
//代码效果参考：http://0791zd.com/bx/art_7839.htmlStringfilename=children[i];
FilenameFilter filter=newFilenameFilter(){
publicbooleanaccept(File dir,Stringname){
return!name.startsWith(".");
children=dir.list(filter);
File[]files=dir.listFiles();
FileFilter fileFilter=newFileFilter(){
publicbooleanaccept(File file){
returnfile.isDirectory();
files=dir.listFiles(fileFilter);
- 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 {
importjava.util.zip.;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( ZipEntry entry = new ZipEntry(name); entry.setMethod(ZipEntry.STORED); entry.setCompressedSize(file.length()); entry.setSize(file.length()); entry.setCrc(crc.getValue()); zos.putNextEntry(entry); zos.write(buffer, 0, bytesRead); zos.close();
importjava.io.;
publicclassZipIt{
publicstaticvoidmain(Stringargs[])throwsIOException{if(args.length<2){ File zipFile=newFile(args[0]); if(zipFile.exists()){ 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); BufferedInputStream bis=newBufferedInputStream( newFileInputStream(file)); while((bytesRead=bis.read(buffer))!=-1){ crc.update(buffer,0,bytesRead); bis=newBufferedInputStream( ZipEntry entry=newZipEntry(name); zos.write(buffer,0,bytesRead); - 解析/读取XML 文件
XML文件
<?xml version="1.0"?>
<name>John</name> <grade>B</grade> <age>12</age><name>Mary</name> <grade>A</grade> <age>11</age> <name>Simon</name> <age>18</age>
Java代码
package net.viralpatel.java.xmlparser;
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) {
}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 = e.getElementsByTagName("age"); System.out.println("Age: " } } } else { System.exit(1); } System.out.println(e); XMLParser parser = new XMLParser(); parser.getAllUserNames("c:\\test.xml");
packagenet.viralpatel.java.xmlparser;
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){DocumentBuilderFactory dbf=DocumentBuilderFactory.newInstance(); DocumentBuilder db=dbf.newDocumentBuilder(); File file=newFile(fileName); if(file.exists()){ Document doc=db.parse(file); Element docEle=doc.getDocumentElement(); +docEle.getNodeName()); NodeList studentList=docEle.getElementsByTagName("student"); .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){ Elemente=(Element)node; NodeList nodeList=e.getElementsByTagName("name"); +nodeList.item(0).getChildNodes().item(0) nodeList=e.getElementsByTagName("grade"); nodeList=e.getElementsByTagName("age"); }else{ XMLParser parser=newXMLParser(); - 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" },
Map countryCapitals = ArrayUtils.toMap(countries);{ "Netherland", "Amsterdam" }, { "Japan", "Tokyo" }, { "France", "Paris" } };
System.out.println("Capital of Japan is " + countryCapitals.get("Japan"));
System.out.println("Capital of France is " + countryCapitals.get("France"));
importjava.util.Map;
importorg.apache.commons.lang.ArrayUtils;
publicclassMain{
publicstaticvoidmain(String[]args){
String[][]countries={ {"United States","New York"},{"United Kingdom","London"},
Map countryCapitals=ArrayUtils.toMap(countries);{"Netherland","Amsterdam"},{"Japan","Tokyo"},{"France","Paris"}};
System.out.println("Capital of Japan is "+countryCapitals.get("Japan"));
System.out.println("Capital of France is "+countryCapitals.get("France")); - 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++)
msg.setRecipients(Message.RecipientType.TO, addressTo);addressTo[i] = new InternetAddress(recipients[i]);
// 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);
importjavax.mail.;
importjavax.mail.internet.;
importjava.util.*;
publicvoidpostMail(Stringrecipients[],Stringsubject,Stringmessage,Stringfrom)throwsMessagingException
booleandebug=false;
Properties props=newProperties();
props.put("mail.smtp.host","smtp.example.com");
Session session=Session.getDefaultInstance(props,null);
Message msg=newMimeMessage(session);
InternetAddress addressFrom=newInternetAddress(from);
InternetAddress[]addressTo=newInternetAddress[recipients.length];
for(inti=0;i<recipients.length;i++)
msg.setRecipients(Message.RecipientType.TO,addressTo);addressTo[i]=newInternetAddress(recipients[i]);
msg.addHeader("MyHeaderName","myHeaderValue");
msg.setContent(message,"text/plain"); - 发送代数据的HTTP 请求
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.net.URL;
public static void main(String[] args) {
importjava.io.BufferedReader;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();
importjava.io.InputStreamReader;
importjava.net.URL;
publicstaticvoidmain(String[]args) {URL my_url=newURL("http://coolshell.cn/"); BufferedReader br=newBufferedReader(newInputStreamReader(my_url.openStream())); StringstrTemp=""; while(null!=(strTemp=br.readLine())){ }catch(Exception ex){ - 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.
*/
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(
int preserveLength = Math.min(oldSize,newSize);elementType,newSize);
if (preserveLength > 0)
return newArray;System.arraycopy (oldArray,0,newArray,0,preserveLength);
// 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++)
privatestaticObjectresizeArray(ObjectoldArray,intnewSize){System.out.println (a[i]);
intoldSize=java.lang.reflect.Array.getLength(oldArray);
ClasselementType=oldArray.getClass().getComponentType();
ObjectnewArray=java.lang.reflect.Array.newInstance(
intpreserveLength=Math.min(oldSize,newSize);
if(preserveLength>0)
returnnewArray;System.arraycopy(oldArray,0,newArray,0,preserveLength);
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]);
