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
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(); }
} }
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
9. 在Java中创建JSON数据
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
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
<?xml 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<a.length; <BR="" i++)=""> System.out.println (a[i]); }
16. 在Java中解析/读取XML文件
view plaincopy to clipboardprint?
<?xml version="1.0"?> <students> <student> <name>John</name> <grade>B</grade> <age>12</age> </student> <student> <name>Mary</name> <grade>A</grade> <age>11</age> </student> <student> <name>Simon</name> <grade>A</grade> <age>18</age> </student> </students>
<?xml version="1.0"?> <students> <student> <name>John</name> <grade>B</grade> <age>12</age> </student> <student> <name>Mary</name> <grade>A</grade> <age>11</age> </student> <student> <name>Simon</name> <grade>A</grade> <age>18</age> </student> </students> Java code to parse above XML.
view plaincopy to clipboardprint?
package net.viralpatel.java.xmlparser;
import java.io.File; import javax.xml.parsers.DocumentBuilder; import javax.xml.parsers.DocumentBuilderFactory;
import org.w3c.dom.Document; import org.w3c.dom.Element; import org.w3c.dom.Node; import org.w3c.dom.NodeList;
public class XMLParser {
public void getAllUserNames(String fileName) { try { DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance(); DocumentBuilder db = dbf.newDocumentBuilder(); File file = new File(fileName); if (file.exists()) { Document doc = db.parse(file); Element docEle = doc.getDocumentElement();
// Print root element of the document System.out.println("Root element of the document: " + docEle.getNodeName());
NodeList studentList = docEle.getElementsByTagName("student");
// Print total student elements in document System.out .println("Total students: " + studentList.getLength());
if (studentList != null && studentList.getLength() > 0) { for (int i = 0; i < studentList.getLength(); i++) {
Node node = studentList.item(i);
if (node.getNodeType() == Node.ELEMENT_NODE) {
System.out .println("=====================");
Element e = (Element) node; NodeList nodeList = e.getElementsByTagName("name"); System.out.println("Name: " + nodeList.item(0).getChildNodes().item(0) .getNodeValue());
nodeList = e.getElementsByTagName("grade"); System.out.println("Grade: " + nodeList.item(0).getChildNodes().item(0) .getNodeValue());
nodeList = e.getElementsByTagName("age"); System.out.println("Age: " + nodeList.item(0).getChildNodes().item(0) .getNodeValue()); } } } else { System.exit(1); } } } catch (Exception e) { System.out.println(e); } } public static void main(String[] args) {
XMLParser parser = new XMLParser(); parser.getAllUserNames("c:\\test.xml"); } }
package net.viralpatel.java.xmlparser;
import java.io.File; import javax.xml.parsers.DocumentBuilder; import javax.xml.parsers.DocumentBuilderFactory;
import org.w3c.dom.Document; import org.w3c.dom.Element; import org.w3c.dom.Node; import org.w3c.dom.NodeList;
public class XMLParser {
public void getAllUserNames(String fileName) { try { DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance(); DocumentBuilder db = dbf.newDocumentBuilder(); File file = new File(fileName); if (file.exists()) { Document doc = db.parse(file); Element docEle = doc.getDocumentElement();
// Print root element of the 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]);
}