本文汇总了多种Java实用技巧，包括字符串与整数互转、文件操作、获取当前调用方法名、日期格式转换等。此外还介绍了如何使用JDBC连接Oracle数据库、创建JSON数据、生成PDF文件等内容。
1. 把Strings转换成int和把int转换成String
String a = String.valueOf(2); //integer to numeric string int i = Integer.parseInt(a); //numeric string to an int
String a = String.valueOf(2); //integer to numeric string int i = Integer.parseInt(a); //numeric string to an int |
2. 向Java文件中添加文本
Updated: Thanks Simone for pointing to exception. I have
changed the code.
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 = new BufferedWriter(new FileWriter(”filename”, true)); out.write(”aString”); } catch (IOException e) { // error processing code } finally { if (out != null) { out.close(); } }
3. 获取Java现在正调用的方法名
String methodName = Thread.currentThread().getStackTrace()[1].getMethodName();
String methodName = Thread.currentThread().getStackTrace()[1].getMethodName (); |
4. 在Java中将String型转换成Date型
java.util.Date = java.text.DateFormat.getDateInstance().parse(date String);
java.util.Date = java.text.DateFormat.getDateInstance().parse(date String);or SimpleDateFormat format = new SimpleDateFormat( "dd.MM.yyyy" ); Date date = format.parse( myString ); SimpleDateFormat format = new SimpleDateFormat( "dd.MM.yyyy" ); Date date = format.parse( myString ); |
5. 通过Java JDBC链接Oracle数据库
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 (); } }
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.将Java中的util.Date转换成sql.Date
这一片段显示如何将一个java util Date转换成sql Date用于数据库
java.util.Date utilDate = new java.util.Date(); java.sql.Date sqlDate = new java.sql.Date (utilDate.getTime());
java.util.Date utilDate = new java.util.Date(); java.sql.Date sqlDate = new java.sql.Date(utilDate.getTime()); |
7. 使用NIO快速复制Java文件
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 ) { & nbsp; position += inChannel.transferTo( position, maxCount, outChannel );
} } finally { if ( inChannel != null ) { & nbsp; inChannel.close(); } if ( outChannel != null ) { & nbsp; outChannel.close(); } } }
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. 在Java中创建缩略图
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 (); }
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.drawImag e(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. 在Java中创建JSON数据
Read this article for more details. Download JAR file 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 (); ...
import org.json.JSONObject; ... ... JSONObject json = new JSONObject(); json.put("city", "Mumbai"); json.put("country", "India"); ... String output = json.toString(); ...
10. 在Java中使用iText JAR打开PDF
Read this article for more details.
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(); } } }
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. 在Java上的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");
Read this article for more details. Update: Thanks Markus for the comment. I have updated the code and changed it to
more robust implementation.
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; } }
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; } } One more implementation of Singleton class. Thanks to Ralph and Lukasz Zielinski
for pointing this out.
public enum SimpleSingleton { INSTANCE; public void doSomething() { } } //Call the method from Singleton: SimpleSingleton.INSTANCE.doSomething();
public enum SimpleSingleton { INSTANCE; public void doSomething() { } }
//Call the method from Singleton: SimpleSingleton.INSTANCE.doSomething();
13. 在Java上做屏幕截图
Read this article for more details.
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)); } ...
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. 在Java中的文件，目录列表
>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);
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. 在Java中创建ZIP和JAR文件
import java.util.zip.*;
import
java.io.*;
public class ZipIt {
public static void main(String args[]) throws IOException
{
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()) {
&
nbsp; System.err.println("Skipping: " + name);
&
nbsp; continue;
}
BufferedInputStream bis = new BufferedInputStream(
&
nbsp; new FileInputStream(file));
crc.reset
();
while
((bytesRead = bis.read(buffer)) != -1) {
&
nbsp; crc.update(buffer, 0, bytesRead);
}
bis.close();
// Reset to
beginning of input stream
bis = new
BufferedInputStream(
&
nbsp; 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) {
&
nbsp; zos.write(buffer, 0, bytesRead);
}
bis.close();
}
zos.close
();
}
}
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); & nbsp; 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); & nbsp; 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. Parsing / Reading XML file in Java Sample XML file.
<!--l version="1.0--> John B 12 Mary A 11 Simon A 18
<!--l version="1.0"? --> John B 12 Mary A < AGE>11 Simon A 18 Java code to parse above XML.
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()) { & nbsp; Document doc = db.parse(file); & nbsp; Element docEle = doc.getDocumentElement(); & nbsp; // Print root element of the document & nbsp; System.out.println("Root element of the document: " & nbsp; + docEle.getNodeName ()); & nbsp; NodeList studentList = docEle.getElementsByTagName ("student"); & nbsp; // Print total student elements in document & nbsp; System.out & nbsp; .println("Total students: " + studentList.getLength()); & nbsp; if (studentList != null && studentList.getLength() > 0) { & nbsp; for (int i = 0; i < studentList.getLength(); i++) { & nbsp; Node node = studentList.item(i); & nbsp; if (node.getNodeType() == Node.ELEMENT_NODE) { & nbsp; System.out & nbsp; .println ("====================="); & nbsp; Element e = (Element) node; & nbsp; NodeList nodeList = e.getElementsByTagName("name"); & nbsp; System.out.println("Name: " & nbsp; + nodeList.item(0).getChildNodes ().item(0) & nbsp; ; .getNodeValue()); & nbsp; nodeList = e.getElementsByTagName("grade"); & nbsp; System.out.println("Grade: " & nbsp; + nodeList.item(0).getChildNodes ().item(0) & nbsp; ; .getNodeValue()); & nbsp; nodeList = e.getElementsByTagName("age"); & nbsp; System.out.println("Age: " & nbsp; + nodeList.item(0).getChildNodes ().item(0) & nbsp; ; .getNodeValue()); & nbsp; } & nbsp; } & nbsp; } else { & nbsp; System.exit(1); & nbsp; } } } catch (Exception e) { System.out.println(e); } } public static void main(String[] args) { XMLParser parser = new XMLParser (); parser.getAllUserNames("c:\\test.xml"); } }
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 &nb sp;.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. Convert Array to Map in Java
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")); } }
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. Send Email using Java
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); }
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. Send HTTP request & fetching data using Java
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://www.viralpatel.net/blogs/");&nbs p; 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(); } } }
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://www.viralpatel.net/blogs/"); 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. Resize an Array in Java
/** * 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 System.out.println (a[i]); }
16. 在Java中解析/读取XML文件
view plaincopy to clipboardprint? <?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>
<?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 code to parse above XML.
view plaincopy to clipboardprint? 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"); } }
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. 在Java中将Array转换成Map
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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"));
}
}
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. 在Java中发送电子邮件
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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);
}
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. 使用Java发送HTTP请求和提取数据
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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://www.viralpatel.net/blogs/");
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();
}
}
}
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://www.viralpatel.net/blogs/"); 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. 在Java中调整数组
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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.
*/
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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