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 |
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();
}
}
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();
}
}
3. 获取Java现在正调用的方法名
String methodName = Thread.currentThread().getStackTrace()[1].getMethodName(); |
4. 在Java中将String型转换成Date型
java.util.Date = java.text.DateFormat.getDateInstance().parse(date String); |
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();
}
}
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()); |
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
-- 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 )
{
&
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, intquality, 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(); } } }