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非常有用的java20个代码片段

日期:2018-05-20点击:305
  1. 因为欣赏所以转载。原文地址http://blog.csdn.net/gdhuyufei/article/details/51319417
  2. 字符串有整型的相互转换
    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 intString a = String.valueOf(2);   //integer to numeric string  
    int i = Integer.parseInt(a); //numeric string to an int1
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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(); } } 
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  1. 得到当前方法的名字
String methodName = Thread.currentThread().getStackTrace()[1].getMethodName(); 
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  1. 转字符串到日期
java.util.Date = java.text.DateFormat.getDateInstance().parse(date String); 或者是: SimpleDateFormat format = new SimpleDateFormat( "dd.MM.yyyy" ); Date date = format.parse( myString ); 
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  1. 使用JDBC链接Oracle
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(); } } 
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  1. 把 Java util.Date 转成 sql.Date
java.util.Date utilDate = new java.util.Date(); java.sql.Date sqlDate = new java.sql.Date(utilDate.getTime()); 
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  1. 使用NIO进行快速的文件拷贝
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. 创建图片的缩略图 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(); } 9. 创建 JSON 格式的数据 ```java import org.json.JSONObject; JSONObject json = new JSONObject(); json.put("city", "Mumbai"); json.put("country", "India"); String output = json.toString(); <div class="se-preview-section-delimiter"></div>  
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  1. 使用iText JAR生成PDF 
    “`java 
    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(); } }  
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11. HTTP 代理设置

阅读这篇 文章 了解更多细节。

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. 单实例Singleton 示例

请先阅读这篇文章 了解更多信息

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; }  
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另一种实现

public enum SimpleSingleton { 
INSTANCE; 
public void doSomething() { 

}

//Call the method from Singleton: 
SimpleSingleton.INSTANCE.doSomething(); 
13. 抓屏程序

阅读这篇文章 获得更多信息。

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. 列出文件和目录

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. 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()) { 
System.err.println(“Skipping: ” + name); 
continue; 

BufferedInputStream bis = new BufferedInputStream( 
new FileInputStream(file)); 
crc.reset(); 
while ((bytesRead = bis.read(buffer)) != -1) { 
crc.update(buffer, 0, bytesRead); 

bis.close(); 
// Reset to beginning of input stream 
bis = new BufferedInputStream( 
new FileInputStream(file)); 
ZipEntry entry = new ZipEntry(name); 
entry.setMethod(ZipEntry.STORED); 
entry.setCompressedSize(file.length()); 
entry.setSize(file.length()); 
entry.setCrc(crc.getValue()); 
zos.putNextEntry(entry); 
while ((bytesRead = bis.read(buffer)) != -1) { 
zos.write(buffer, 0, bytesRead); 

bis.close(); 

zos.close(); 


16. 解析/读取XML 文件

XML文件

10. 使用iText JAR生成PDF ```java 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();  } } } <div class="se-preview-section-delimiter"></div>  
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  1. HTTP 代理设置 
    “`java 
    System.getProperties().put(“http.proxyHost”, “someProxyURL”); 
    System.getProperties().put(“http.proxyPort”, “someProxyPort”); 
    System.getProperties().put(“http.proxyUser”, “someUserName”); 
    System.getProperties().put(“http.proxyPassword”, “somePassword”);
  2. 单实例Singleton 示例

请先阅读这篇文章 了解更多信息

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; }  
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另一种实现

public enum SimpleSingleton { 
INSTANCE; 
public void doSomething() { 

}

//Call the method from Singleton: 
SimpleSingleton.INSTANCE.doSomething(); 
13. 抓屏程序

阅读这篇文章 获得更多信息。

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. 列出文件和目录

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. 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()) { 
System.err.println(“Skipping: ” + name); 
continue; 

BufferedInputStream bis = new BufferedInputStream( 
new FileInputStream(file)); 
crc.reset(); 
while ((bytesRead = bis.read(buffer)) != -1) { 
crc.update(buffer, 0, bytesRead); 

bis.close(); 
// Reset to beginning of input stream 
bis = new BufferedInputStream( 
new FileInputStream(file)); 
ZipEntry entry = new ZipEntry(name); 
entry.setMethod(ZipEntry.STORED); 
entry.setCompressedSize(file.length()); 
entry.setSize(file.length()); 
entry.setCrc(crc.getValue()); 
zos.putNextEntry(entry); 
while ((bytesRead = bis.read(buffer)) != -1) { 
zos.write(buffer, 0, bytesRead); 

bis.close(); 

zos.close(); 


16. 解析/读取XML 文件

XML文件

11. HTTP 代理设置 ```java System.getProperties().put("http.proxyHost", "someProxyURL");  System.getProperties().put("http.proxyPort", "someProxyPort");  System.getProperties().put("http.proxyUser", "someUserName");  System.getProperties().put("http.proxyPassword", "somePassword"); <div class="se-preview-section-delimiter"></div>  
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  1. 单实例Singleton 示例

请先阅读这篇文章 了解更多信息

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; }  
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另一种实现

public enum SimpleSingleton { 
INSTANCE; 
public void doSomething() { 

}

//Call the method from Singleton: 
SimpleSingleton.INSTANCE.doSomething(); 
13. 抓屏程序

阅读这篇文章 获得更多信息。

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. 列出文件和目录

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. 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()) { 
System.err.println(“Skipping: ” + name); 
continue; 

BufferedInputStream bis = new BufferedInputStream( 
new FileInputStream(file)); 
crc.reset(); 
while ((bytesRead = bis.read(buffer)) != -1) { 
crc.update(buffer, 0, bytesRead); 

bis.close(); 
// Reset to beginning of input stream 
bis = new BufferedInputStream( 
new FileInputStream(file)); 
ZipEntry entry = new ZipEntry(name); 
entry.setMethod(ZipEntry.STORED); 
entry.setCompressedSize(file.length()); 
entry.setSize(file.length()); 
entry.setCrc(crc.getValue()); 
zos.putNextEntry(entry); 
while ((bytesRead = bis.read(buffer)) != -1) { 
zos.write(buffer, 0, bytesRead); 

bis.close(); 

zos.close(); 


16. 解析/读取XML 文件

XML文件

12. 单实例Singleton 示例 ```java 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; } } <div class="se-preview-section-delimiter"></div>  
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另一种实现

public enum SimpleSingleton { 
INSTANCE; 
public void doSomething() { 

}

//Call the method from Singleton: 
SimpleSingleton.INSTANCE.doSomething(); 
13. 抓屏程序

阅读这篇文章 获得更多信息。

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. 列出文件和目录

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. 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()) { 
System.err.println(“Skipping: ” + name); 
continue; 

BufferedInputStream bis = new BufferedInputStream( 
new FileInputStream(file)); 
crc.reset(); 
while ((bytesRead = bis.read(buffer)) != -1) { 
crc.update(buffer, 0, bytesRead); 

bis.close(); 
// Reset to beginning of input stream 
bis = new BufferedInputStream( 
new FileInputStream(file)); 
ZipEntry entry = new ZipEntry(name); 
entry.setMethod(ZipEntry.STORED); 
entry.setCompressedSize(file.length()); 
entry.setSize(file.length()); 
entry.setCrc(crc.getValue()); 
zos.putNextEntry(entry); 
while ((bytesRead = bis.read(buffer)) != -1) { 
zos.write(buffer, 0, bytesRead); 

bis.close(); 

zos.close(); 


16. 解析/读取XML 文件

XML文件

另一种实现 ```java public enum SimpleSingleton { INSTANCE; public void doSomething() { } } //Call the method from Singleton:  SimpleSingleton.INSTANCE.doSomething(); <div class="se-preview-section-delimiter"></div>  
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  1. 抓屏程序

阅读这篇文章 获得更多信息。

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. 列出文件和目录

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. 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()) { 
System.err.println(“Skipping: ” + name); 
continue; 

BufferedInputStream bis = new BufferedInputStream( 
new FileInputStream(file)); 
crc.reset(); 
while ((bytesRead = bis.read(buffer)) != -1) { 
crc.update(buffer, 0, bytesRead); 

bis.close(); 
// Reset to beginning of input stream 
bis = new BufferedInputStream( 
new FileInputStream(file)); 
ZipEntry entry = new ZipEntry(name); 
entry.setMethod(ZipEntry.STORED); 
entry.setCompressedSize(file.length()); 
entry.setSize(file.length()); 
entry.setCrc(crc.getValue()); 
zos.putNextEntry(entry); 
while ((bytesRead = bis.read(buffer)) != -1) { 
zos.write(buffer, 0, bytesRead); 

bis.close(); 

zos.close(); 


16. 解析/读取XML 文件

XML文件

13. 抓屏程序 阅读这篇文章 获得更多信息。 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. 列出文件和目录 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. 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()) { System.err.println("Skipping: " + name); continue; } BufferedInputStream bis = new BufferedInputStream( new FileInputStream(file)); crc.reset(); while ((bytesRead = bis.read(buffer)) != -1) { crc.update(buffer, 0, bytesRead); } bis.close(); // Reset to beginning of input stream  bis = new BufferedInputStream( new FileInputStream(file)); ZipEntry entry = new ZipEntry(name); entry.setMethod(ZipEntry.STORED); entry.setCompressedSize(file.length()); entry.setSize(file.length()); entry.setCrc(crc.getValue()); zos.putNextEntry(entry); while ((bytesRead = bis.read(buffer)) != -1) { zos.write(buffer, 0, bytesRead); } bis.close(); } zos.close(); } } 
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  1. 解析/读取XML 文件

XML文件

/** * 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]); }
原文链接:https://yq.aliyun.com/articles/594567
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