20非常有用的Java程序片段(2)

9. 创建 JSON 格式的数据

请先阅读这篇文章 了解一些细节，
并下面这个JAR 文件：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();
...

10. 使用iText JAR生成PDF

阅读这篇文章 了解更多细节

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. 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");

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;
    }
}

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);