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Java开发人员常用的20个java功能
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 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;
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 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 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.
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.
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()) {
& 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 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
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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[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.
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