常用 java 代码总结
1. 把 Strings 转换成 int 及把 int 转换成 String
//将整型转为字符串型 String str = String.valueOf(2);
//将字符型转为整型 int i = Integer.parseInt("2");
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();
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);
java.util.Date = java.text.DateFormat.getDateInstance().parse(date String);or SimpleDateFormat format = new SimpleDateFormat( "dd.MM.yyyy" ); Date date = format.parse( myString ); SimpleDateFormat format = new SimpleDateFormat( "dd.MM.yyyy" ); Date date = format.parse( myString );
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 将 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());
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(), // original
outChannel);
-- 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, 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
BufferedIm
age thumbImage = new BufferedImage(thumbWidth, thumbHeight,
BufferedImage.TYPE_INT_RGB); Graphics2D graphics2D = thumbImage.crea
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