java

版权声明：本文为博主原创文章，遵循 CC 4.0 by-sa 版权协议，转载请附上原文出处链接和本声明。 本文链接：https://blog.csdn.net/hyg1234456789/article/details/84588486 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 stringint 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;

3ff7 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

filenameImage 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

HEIGHTdouble 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-

flyBufferedImage 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

outFilenameBufferedOutputStream 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");
12. Java Singleton 例子

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 SimpleSingletonpublic 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

directoryString 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

objectsFile[] files = dir.listFiles();
// This filter only returns directoriesFileFilter 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

streambis =

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 JavaSample XML file.




John

B

12



Mary

A

11



Simon

A

18


JohnB12MaryA<

AGE>11SimonA18

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.Docu 4000 ment; 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

documentSystem.out.println("Root element of the

document: "+ docEle.getNodeName());
NodeList studentList = docEle.getElementsByTagName
("student");
// Print total student elements in

documentSystem.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 addressProperties props = new Properties();props.put

("mail.smtp.host", "smtp.example.com");
// create some properties and get the default

SessionSession session = Session.getDefaultInstance(props,

null);session.setDebug(debug);
// create a messageMessage msg = new

MimeMessage(session);
// set the from and to addressInternetAddress 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 Wantmsg.addHeader("MyHeaderName",

"myHeaderValue");
// Setting the Subject and Content Typemsg.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 documentSystem.out.println("Root element of the document: "+ docEle.getNodeName());
NodeList studentList = docEle.getElementsByTagName("student");
// Print total student elements in documentSystem.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) {
Sy 4000 stem.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 addressProperties props = new Properties();props.put("mail.smtp.host", "smtp.example.com");
// create some properties and get the default SessionSession session = Session.getDefaultInstance(props, null);session.setDebug(debug);
// create a messageMessage msg = new MimeMessage(session);
// set the from and to addressInternetAddress 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 Wantmsg.addHeader("MyHeaderName", "myHeaderValue");
// Setting the Subject and Content Typemsg.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.