20个开发人员非常有用的Java功能代码(二)-阿里云开发者社区

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;
}
}

// 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;
}
}
// 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;
File file = new File(name);
if (!file.exists()) {
   System.err.println("Skipping: " + name);
   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);
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();
}
}

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;
File file = new File(name);
if (!file.exists()) {
   System.err.println("Skipping: " + name);
    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);
  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.

John
B
12

Mary
A
11

Simon
A
18

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()) {
   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. 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 = new InternetAddress(recipients);
}
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 = new InternetAddress(recipients);
}
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/"); 
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

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.
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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 = new InternetAddress(recipients);
}
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 = new InternetAddress(recipients);
}
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);

}

本文转自My_King1 51CTO博客，原文链接：http://blog.51cto.com/apprentice/1360616，如需转载请自行联系原作者

20个开发人员非常有用的Java功能代码(二)

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