常用Java程序片段
1、改变数组的大小
package com.js.ai.modules.jsa.test;
public class Testxf {
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;
}
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.print (a[i]+";");
}
}
2、发送代数据的HTTP 请求
package com.js.ai.modules.jsa.test;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.net.URL;
public class Testxf {
public static void main(String[] args) {
try {
URL my_url=new URL("https://open.alipay.com/platform/home.htm");
BufferedReader br=new BufferedReader(new InputStreamReader(my_url.openStream()));
String strTemp = "";
while(null!=(strTemp=br.readLine())){
System.out.println(strTemp);
}
} catch (Exception e) {
e.printStackTrace();
}
}
}
3、发送邮件
package com.js.ai.modules.jsa.test;
import java.util.Properties;
import javax.mail.Message;
import javax.mail.MessagingException;
import javax.mail.Session;
import javax.mail.Transport;
import javax.mail.internet.InternetAddress;
import javax.mail.internet.MimeMessage;
public class Testxf {
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);
}
}
4、把 Array 转换成 Map
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"));
}
5、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：
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");
}
}
6、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);
7、抓屏程序
package com.js.ai.modules.jsa.test;
import java.awt.Dimension;
import java.awt.Rectangle;
import java.awt.Robot;
import java.awt.Toolkit;
import java.awt.image.BufferedImage;
import java.io.File;
import javax.imageio.ImageIO;
public class Testxf {
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));
}
public static void main(String[] args) throws Exception {
Testxf testxf =new Testxf();
testxf.captureScreen("C:/Users/Administrator/Desktop/JSAxfz/captureScreen.png");
}
}
8、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();
}
}
}
9、使用NIO进行快速的文件拷贝
package com.js.ai.modules.jsa.test;
import java.awt.Container;
import java.awt.Graphics2D;
import java.awt.Image;
import java.awt.MediaTracker;
import java.awt.RenderingHints;
import java.awt.Toolkit;
import java.awt.image.BufferedImage;
import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.nio.channels.FileChannel;
import javax.imageio.ImageIO;
public class Testxf {
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();
}
}
}
public static void main(String[] args) throws IOException {
Testxf testxf =new Testxf();
File in=new File("C:/Users/Administrator/Desktop/JSAxfz/yuan.txt");
File out=new File("C:/Users/Administrator/Desktop/JSAxfz/copy.txt");
testxf.fileCopy(in, out);
}
}
10、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();
}
}
