常用java代码

1  int 和 String 相互转换：

String a = String.valueOf(2);//integer　 to　numeric　string　　　  
  int i = Integer.parseInt(a);//numeric string　to　an　int  

2 向文件中写入文本：

BufferedWriter out = null;
		try {
			out = new BufferedWriter(new FileWriter("filename", true));
			out.write("aString");
		} catch (IOException e) {
			// 　error　processing　code　　　
		} finally {
			if (out != null) {
				try {
					out.close();
				} catch (IOException e) {
					e.printStackTrace();
				}
			}
		}

3 java代码截屏：

import java.awt.Dimension;
import java.awt.Rectangle;
import java.awt.Robot;
import java.awt.Toolkit;
import java.awt.image.BufferedImage;
import java.io.File;

import javax.imageio.ImageIO;

/*******************************************************************
 * 用Java实现屏幕截图
 * 该JavaBean可以直接在其他Java应用程序中调用，实现屏幕的"拍照"
 *****************************************************/

public class GuiCamera {
	private String fileName; // 文件的前缀
	private String defaultName = "GuiCamera";
	static int serialNum = 0;
	private String imageFormat; // 图像文件的格式
	private String defaultImageFormat = "png";
	Dimension d = Toolkit.getDefaultToolkit().getScreenSize();

	/****************************************************************
	 * 默认的文件前缀为GuiCamera，文件格式为PNG格式 The default construct will use the default
	 * Image file surname "GuiCamera", and default image format "png"
	 ****************************************************************/
	public GuiCamera() {
		fileName = defaultName;
		imageFormat = defaultImageFormat;

	}

	/****************************************************************
	 * @param s
	 *            the surname of the snapshot file
	 * @param format
	 *            the format of the image file, it can be "jpg" or "png"
	 *            本构造支持JPG和PNG文件的存储
	 ****************************************************************/
	public GuiCamera(String s, String format) {

		fileName = s;
		imageFormat = format;
	}

	/****************************************************************
	 * 对屏幕进行拍照 snapShot the Gui once
	 ****************************************************************/
	public void snapShot() {

		try {
			// 拷贝屏幕到一个BufferedImage对象screenshot
			BufferedImage screenshot = (new Robot())
					.createScreenCapture(new Rectangle(0, 0,
							(int) d.getWidth(), (int) d.getHeight()));
			serialNum++;
			// 根据文件前缀变量和文件格式变量，自动生成文件名
			String name = fileName + String.valueOf(serialNum) + "."
					+ imageFormat;
			File f = new File(name);
			System.out.print("Save File " + name);
			// 将screenshot对象写入图像文件
			ImageIO.write(screenshot, imageFormat, f);
			System.out.print("..Finished!/n");
		} catch (Exception ex) {
			System.out.println(ex);
		}
	}

	public static void main(String[] args) {
		GuiCamera cam = new GuiCamera("d://Hello", "png");//
		cam.snapShot();
	}
}

4 java创建zip和jar：

import java.awt.Dimension;
import java.awt.Rectangle;
import java.awt.Robot;
import java.awt.Toolkit;
import java.awt.image.BufferedImage;
import java.io.File;

import javax.imageio.ImageIO;

/*******************************************************************
 * 用Java实现屏幕截图
 * 该JavaBean可以直接在其他Java应用程序中调用，实现屏幕的"拍照"
 *****************************************************/

public class GuiCamera {
	private String fileName; // 文件的前缀
	private String defaultName = "GuiCamera";
	static int serialNum = 0;
	private String imageFormat; // 图像文件的格式
	private String defaultImageFormat = "png";
	Dimension d = Toolkit.getDefaultToolkit().getScreenSize();

	/****************************************************************
	 * 默认的文件前缀为GuiCamera，文件格式为PNG格式 The default construct will use the default
	 * Image file surname "GuiCamera", and default image format "png"
	 ****************************************************************/
	public GuiCamera() {
		fileName = defaultName;
		imageFormat = defaultImageFormat;

	}

	/****************************************************************
	 * @param s
	 *            the surname of the snapshot file
	 * @param format
	 *            the format of the image file, it can be "jpg" or "png"
	 *            本构造支持JPG和PNG文件的存储
	 ****************************************************************/
	public GuiCamera(String s, String format) {

		fileName = s;
		imageFormat = format;
	}

	/****************************************************************
	 * 对屏幕进行拍照 snapShot the Gui once
	 ****************************************************************/
	public void snapShot() {

		try {
			// 拷贝屏幕到一个BufferedImage对象screenshot
			BufferedImage screenshot = (new Robot())
					.createScreenCapture(new Rectangle(0, 0,
							(int) d.getWidth(), (int) d.getHeight()));
			serialNum++;
			// 根据文件前缀变量和文件格式变量，自动生成文件名
			String name = fileName + String.valueOf(serialNum) + "."
					+ imageFormat;
			File f = new File(name);
			System.out.print("Save File " + name);
			// 将screenshot对象写入图像文件
			ImageIO.write(screenshot, imageFormat, f);
			System.out.print("..Finished!/n");
		} catch (Exception ex) {
			System.out.println(ex);
		}
	}

	public static void main(String[] args) {
		GuiCamera cam = new GuiCamera("d://Hello", "png");//
		cam.snapShot();
	}
}

5 创建图片缩略图

public 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();
	}

6 发送http请求和提取数据

try {
			URL my_url = new URL("www.baidu.com/");
			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();
		}

7 获取目录列表

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);

8 Array 转 Map：

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"));

9 导出excel：http://blog.csdn.net/luqin1988/article/details/7680520