常用的Java代码汇总

文章作者：lz201234

1. 字符串有整型的相互转换

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

2. 向文件末尾添加内容

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1. BufferedWriter out = null;
2. try {
3. out = new BufferedWriter(new FileWriter(”filename”, true));
4. out.write(”aString”);
5. } catch (IOException e) {
6. // error processing code
7. } finally {
8. if (out != null) {
9. out.close();
10. }
11. }

3. 得到当前方法的名字

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1. <span style="font-family:Arial;font-size:14px;">String methodName = Thread.currentThread().getStackTrace()[1].getMethodName(); </span>

4. 转字符串到日期

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1. java.util.Date = java.text.DateFormat.getDateInstance().parse(date String);

或者是：

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1. SimpleDateFormat format = new SimpleDateFormat( "dd.MM.yyyy" );
2. Date date = format.parse( myString );

5. 使用JDBC链接Oracle

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1. public class OracleJdbcTest
2. {
3. String driverClass = "oracle.jdbc.driver.OracleDriver";
5. Connection con;
7. public void init(FileInputStream fs) throws ClassNotFoundException, SQLException, FileNotFoundException, IOException
8. {
9. Properties props = new Properties();
10. props.load(fs);
11. String url = props.getProperty("db.url");
12. String userName = props.getProperty("db.user");
13. String password = props.getProperty("db.password");
14. Class.forName(driverClass);
16. con=DriverManager.getConnection(url, userName, password);
17. }
19. public void fetch() throws SQLException, IOException
20. {
21. PreparedStatement ps = con.prepareStatement("select SYSDATE from dual");
22. ResultSet rs = ps.executeQuery();
24. while (rs.next())
25. {
26. // do the thing you do
27. }
28. rs.close();
29. ps.close();
30. }
32. public static void main(String[] args)
33. {
34. OracleJdbcTest test = new OracleJdbcTest();
35. test.init();
36. test.fetch();
37. }
38. }

6. 把 Java util.Date 转成 sql.Date

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1. <span style="font-family:Arial;font-size:14px;">java.util.Date utilDate = new java.util.Date();
2. java.sql.Date sqlDate = new java.sql.Date(utilDate.getTime());</span>

7. 使用NIO进行快速的文件拷贝

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1. public static void fileCopy( File in, File out )
2. throws IOException
3. {
4. FileChannel inChannel = new FileInputStream( in ).getChannel();
5. FileChannel outChannel = new FileOutputStream( out ).getChannel();
6. try
7. {
8. // inChannel.transferTo(0, inChannel.size(), outChannel); // original -- apparently has trouble copying large files on Windows
10. // magic number for Windows, 64Mb - 32Kb)
11. int maxCount = (64 * 1024 * 1024) - (32 * 1024);
12. long size = inChannel.size();
13. long position = 0;
14. while ( position < size )
15. {
16. position += inChannel.transferTo( position, maxCount, outChannel );
17. }
18. }
19. finally
20. {
21. if ( inChannel != null )
22. {
23. inChannel.close();
24. }
25. if ( outChannel != null )
26. {
27. outChannel.close();
28. }
29. }
30. }

8. 创建图片的缩略图

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1. private void createThumbnail(String filename, int thumbWidth, int thumbHeight, int quality, String outFilename)
2. throws interruptedException, FileNotFoundException, IOException
3. {
4. // load image from filename
5. Image image = Toolkit.getDefaultToolkit().getImage(filename);
6. MediaTracker mediaTracker = new MediaTracker(new Container());
7. mediaTracker.addImage(image, 0);
8. mediaTracker.waitForID(0);
9. // use this to test for errors at this point: System.out.println(mediaTracker.isErrorAny());
11. // determine thumbnail size from WIDTH and HEIGHT
12. double thumbRatio = (double)thumbWidth / (double)thumbHeight;
13. int imageWidth = image.getWidth(null);
14. int imageHeight = image.getHeight(null);
15. double imageRatio = (double)imageWidth / (double)imageHeight;
16. if (thumbRatio < imageRatio) {
17. thumbHeight = (int)(thumbWidth / imageRatio);
18. } else {
19. thumbWidth = (int)(thumbHeight * imageRatio);
20. }
22. // draw original image to thumbnail image object and
23. // scale it to the new size on-the-fly
24. BufferedImage thumbImage = new BufferedImage(thumbWidth, thumbHeight, BufferedImage.TYPE_INT_RGB);
25. Graphics2D graphics2D = thumbImage.createGraphics();
26. graphics2D.setRenderingHint(RenderingHints.KEY_INTERPOLATION, RenderingHints.VALUE_INTERPOLATION_BILINEAR);
27. graphics2D.drawImage(image, 0, 0, thumbWidth, thumbHeight, null);
29. // save thumbnail image to outFilename
30. BufferedOutputStream out = new BufferedOutputStream(new FileOutputStream(outFilename));
31. JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(out);
32. JPEGEncodeParam param = encoder.getDefaultJPEGEncodeParam(thumbImage);
33. quality = Math.max(0, Math.min(quality, 100));
34. param.setQuality((float)quality / 100.0f, false);
35. encoder.setJPEGEncodeParam(param);
36. encoder.encode(thumbImage);
37. out.close();
38. }

9.创建 JSON 格式的数据

并下面这个JAR 文件：json-rpc-1.0.jar (75 kb)/http://t.cn/Rz0bhUA

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1. import org.json.JSONObject;
2. ...
3. ...
4. JSONObject json = new JSONObject();
5. json.put("city", "Mumbai");
6. json.put("country", "India");
7. ...
8. String output = json.toString();
9. ...

10. 使用iText JAR生成PDF

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1. import java.io.File;
2. import java.io.FileOutputStream;
3. import java.io.OutputStream;
4. import java.util.Date;
6. import com.lowagie.text.Document;
7. import com.lowagie.text.Paragraph;
8. import com.lowagie.text.pdf.PdfWriter;
10. public class GeneratePDF {
12. public static void main(String[] args) {
13. try {
14. OutputStream file = new FileOutputStream(new File("C:\Test.pdf"));
16. Document document = new Document();
17. PdfWriter.getInstance(document, file);
18. document.open();
19. document.add(new Paragraph("Hello Kiran"));
20. document.add(new Paragraph(new Date().toString()));
22. document.close();
23. file.close();
25. } catch (Exception e) {
27. e.printStackTrace();
28. }
29. }
30. }

11. HTTP 代理设置

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1. System.getProperties().put("http.proxyHost", "someProxyURL");
2. System.getProperties().put("http.proxyPort", "someProxyPort");
3. System.getProperties().put("http.proxyUser", "someUserName");
4. System.getProperties().put("http.proxyPassword", "somePassword");

12. 单实例Singleton 示例

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1. public class SimpleSingleton {
2. private static SimpleSingleton singleInstance = new SimpleSingleton();
4. //Marking default constructor private
5. //to avoid direct instantiation.
6. private SimpleSingleton() {
7. }
9. //Get instance for class SimpleSingleton
10. public static SimpleSingleton getInstance() {
12. return singleInstance;
13. }
14. }

另一种实现

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1. public enum SimpleSingleton {
2. INSTANCE;
3. public void doSomething() {
4. }
5. }
7. //Call the method from Singleton:
8. SimpleSingleton.INSTANCE.doSomething();

13. 抓屏程序

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1. import java.awt.Dimension;
2. import java.awt.Rectangle;
3. import java.awt.Robot;
4. import java.awt.Toolkit;
5. import java.awt.image.BufferedImage;
6. import javax.imageio.ImageIO;
7. import java.io.File;
9. ...
11. public void captureScreen(String fileName) throws Exception {
13. Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();
14. Rectangle screenRectangle = new Rectangle(screenSize);
15. Robot robot = new Robot();
16. BufferedImage image = robot.createScreenCapture(screenRectangle);
17. ImageIO.write(image, "png", new File(fileName));
19. }
20. ...

14. 列出文件和目录

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1. File dir = new File("directoryName");
2. String[] children = dir.list();
3. if (children == null) {
4. // Either dir does not exist or is not a directory
5. } else {
6. for (int i=0; i < children.length; i++) {
7. // Get filename of file or directory
8. String filename = children;
9. }
10. }
12. // It is also possible to filter the list of returned files.
13. // This example does not return any files that start with `.'.
14. FilenameFilter filter = new FilenameFilter() {
15. public boolean accept(File dir, String name) {
16. return !name.startsWith(".");
17. }
18. };
19. children = dir.list(filter);
21. // The list of files can also be retrieved as File objects
22. File[] files = dir.listFiles();
24. // This filter only returns directories
25. FileFilter fileFilter = new FileFilter() {
26. public boolean accept(File file) {
27. return file.isDirectory();
28. }
29. };
30. files = dir.listFiles(fileFilter);