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澳門黃金城官網網:20個開發人員非常有用的Java功能代碼

?

1. 把Strings轉換成int和把int轉換成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. 獲取Java現在正調用的措施名

String methodName =

Thread.currentThread().getStackTrace()[1].getMethodName();

String methodName = Thread.currentThread().getStackTrace()[1].getMethodName

();

4. 在Java中將String型轉換成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. 經由過程Java JDBC鏈接Oracle數據庫

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(FileInput澳門黃金城官網網Stream 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.將Java中的util.Date轉換成sql.Date

這一片段顯示若何將一個java util Date轉換成sql Date用于數據庫

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. 應用NIO快速復制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

8. 在Java中創建縮略圖

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

9. 在Java中創建JSON數據

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.toStr澳門黃金城官網網ing

();

...

import org.json.JSONObject;

...

...

JSONObject json = new

JSONObject();

json.put("city", "Mumbai");

json.put("country",

"India");

...

String output = json.toString();

...

10. 在Java中應用iText JAR打開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代理設置

System.getProperties().put("http.proxyHost",

"someProxyURL");

System.getProperties().put("http.proxyPort",

"someProxyPort");

System.getProperties().put("http.proxyUser",

"someUserName");

System.getProperti澳門黃金城官網網es().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 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 {

IN澳門黃金城官網網STANCE;

public void

doSomething() {

}

}

//Call the method from Singleton:

SimpleSingleton.INSTANCE.doSomething();

13. 在Java上做屏幕截圖

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,目錄列表

>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

15. 在Java中創建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

John

B

12

Mary

A

11

Simon

A

18

John

B

12

Mary

A

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; i0) {

for (int i = 0; i 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

oldArraythe old array, to be reallocated.

* @param

newSizethe new array size.

*

@returnA 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; iSystem.out.println (a[i]);

}

16. 在Java中解析/讀取XML文件

view plaincopy to clipboardprint?

John

B

12

Mary

A

11

Simon

A

18

John

B

12

Mary

A

11

Simon

A

18

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; i0) {

for (int i = 0; i

17. 在Java中將Array轉換成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中發送電子郵件

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

19. 應用Java發送HTTP哀乞降提取數據

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/b澳門黃金城官網網logs/");

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中調劑數組

view plaincopy to clipboardprint?

/**

* Reallocates an array with a new size, and copies the contents

* of the old array to the new array.

* @param oldArraythe old array, to be reallocated.

* @param newSizethe new array size.

* @returnA 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

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