20个开发人员非常有用的Java功能代码

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 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(); 
 
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 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, 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 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");

 

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 {
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

 

 

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<?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 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]);  
}