java经典题目

网络上看到的,觉得不错,转载了。。

  • 本文将为大家介绍20人员非常有用的Java功能代码。这20段代码,可以成为大家在今后的开发过程中,Java编程手册的重要部分。
  •  


    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 

     

     这无非就是各个类型之间的转换。没啥好说的。

    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();  
    }  

     

     

     

     字节流,字符流,管道问题,如何包装的,我需要去看这些书了。

    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 ();

    Thread类里面有个静态方法,获得线程的堆栈,获取堆栈里面的最上面一个的名字。 

    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 ); 

     这个例子没看清楚,估计不是很准确,但是意思大概清楚,无非是类型转换,前面两句我没用过,SimpleDateFormat format = new SimpleDateFormat( "dd-MM-yyyy" );  
    Date date = format.parse( myString );就 可以了,注意 format里面只有parse,没有parseInt或者parseString之分,他有些重载的方法,可以传入各个值。

    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();
    }
    }

     

    不说了,面试的时候一般会用到,实际应用基本不会用到啦。这些工具类个人有个人的写法。别人写了你应该觉得别扭吧,呵呵

    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());

    就一个方法的问题,学习了! 

    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 
    // 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.

     



    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.



     
     
     
    John 

    12 
     
     
    Mary 

    11 
     
     
    Simon 

    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

     

     

    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

     

    view plaincopy to clipboardprint?

    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

     

    view plaincopy to clipboardprint?

    import javax.mail.*;  
    import javax.mail.internet.*;  
    import java.util.*;  

    public void postMail( String recipients[ ], String subject, String message , String from) throws MessagingException  
    {  
    boolean debug = false;  

    //Set the host smtp address  
    Properties props = new Properties();  
    props.put("mail.smtp.host", "smtp.example.com");  

    // create some properties and get the default Session  
    Session session = Session.getDefaultInstance(props, null);  
    session.setDebug(debug);  

    // create a message  
    Message msg = new MimeMessage(session);  

    // set the from and to address  
    InternetAddress addressFrom = new InternetAddress(from);  
    msg.setFrom(addressFrom);  

    InternetAddress[] addressTo = new InternetAddress[recipients.length];  
    for (int i = 0; i < 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

     

    view plaincopy to clipboardprint?

    import java.io.BufferedReader;  
    import java.io.InputStreamReader;  
    import java.net.URL;  

    public class Main {  
    public static void main(String[] args)  {  
    try {  
    URL my_url = new URL("http://www.viralpatel.net/blogs/");  
    BufferedReader br = new BufferedReader(new InputStreamReader(my_url.openStream()));  
    String strTemp = "";  
    while(null != (strTemp = br.readLine())){  
    System.out.println(strTemp);  
    }  
    } catch (Exception ex) {  
    ex.printStackTrace();  
    }  
    }  

     


    import java.io.BufferedReader;
    import java.io.InputStreamReader;
    import java.net.URL;

    public class Main {
    public static void main(String[] args)  {
    try {
    URL my_url = new URL("http://www.viralpatel.net/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

     

    view plaincopy to clipboardprint?

    /** 
    * 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<a.length; i++)  
    System.out.println (a[i]);  

     

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