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 |
2. 向Java文件中添加文本
Updated: Thanks Simone for pointing to exception. I have
changed the code.
BufferedWriter ut = 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 ut = 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(); |
4. 在Java中将String型转换成Date型
java.util.Date = java.text.DateFormat.getDateInstance().parse(date String); |
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()); |
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 utChannel = 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 utChannel = 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, intquality, 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 ut = 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 ut = 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 utput = json.toString (); ...
import org.json.JSONObject; ... ... JSONObject json = new JSONObject(); json.put("city", "Mumbai"); json.put("country", "India"); ... String utput = 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 tomore 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 ldSize =
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
view plaincopy to clipboardprint?
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
view plaincopy to clipboardprint?
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
view plaincopy to clipboardprint?
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
view plaincopy to clipboardprint?
/**
* 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 ldSize = 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]);
}