java经典题目

于 2011-02-15 10:24:00 发布
阅读量977 收藏
点赞数
文章标签： java string import file properties exception

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  


    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

     

     

    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]);   
    } 

     

javazw123
关注
评论
添加红包

请填写红包祝福语或标题

个

红包个数最小为10个

元

红包金额最低5元

当前余额3.43元 前往充值 >
需支付：10.00元
成就一亿技术人!
领取后你会自动成为博主和红包主的粉丝 规则
hope_wisdom
发出的红包
实付元
使用余额支付
点击重新获取
扫码支付
钱包余额 0

抵扣说明：

1.余额是钱包充值的虚拟货币，按照1:1的比例进行支付金额的抵扣。
2.余额无法直接购买下载，可以购买VIP、付费专栏及课程。

余额充值