20非常有用的Java程序片段 (上)

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下面是20个非常有用的Java程序片段，希望能对你有用。

1. 字符串有整型的相互转换

1.
 
2.
String a = String.valueOf(
2
);   
//integer to numeric string  

3.
int
 i = Integer.parseInt(a); 
//numeric string to an int

2. 向文件末尾添加内容

01.
 
02.
BufferedWriter out = 
null
;  

03.
try
 {  

04.
    
out = 
new
 BufferedWriter(
new
 FileWriter(”filename”, 
true
));  

05.
    
out.write(”aString”);  

06.
} 
catch
 (IOException e) {  

07.
    
// error processing code  

08.
} 
finally
 {  

09.
    
if
 (out != 
null
) {  

10.
        
out.close();  

11.
    
}  

12.
}

3. 得到当前方法的名字

1. String methodName = Thread.currentThread().getStackTrace()[ 1 ].getMethodName();

4. 转字符串到日期

1.

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

或者是：

1.
 
2.
SimpleDateFormat format = 
new
 SimpleDateFormat( 
"dd.MM.yyyy"
 );  

3.
Date date = format.parse( myString );

5. 使用JDBC链接Oracle

01.
public
 class
 OracleJdbcTest  

02.
{  

03.
    
String driverClass = 
"oracle.jdbc.driver.OracleDriver"
;  

04.
 
05.
    
Connection con;  

06.
 
07.
    
public
 void
 init(FileInputStream fs) 
throws
 ClassNotFoundException, SQLException, FileNotFoundException, IOException  

08.
    
{  

09.
        
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);  

15.
 
16.
        
con=DriverManager.getConnection(url, userName, password);  

17.
    
}  

18.
 
19.
    
public
 void
 fetch() 
throws
 SQLException, IOException  

20.
    
{  

21.
        
PreparedStatement ps = con.prepareStatement(
"select SYSDATE from dual"
);  

22.
        
ResultSet rs = ps.executeQuery();  

23.
 
24.
        
while
 (rs.next())  

25.
        
{  

26.
            
// do the thing you do  

27.
        
}  

28.
        
rs.close();  

29.
        
ps.close();  

30.
    
}  

31.
 
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

1. java.util.Date utilDate = new java.util.Date();

2. java.sql.Date sqlDate = new java.sql.Date(utilDate.getTime());

7. 使用NIO进行快速的文件拷贝

01.
public
 static
 void
 fileCopy( File in, File out )  

02.
            
throws
 IOException  

03.
    
{  

04.
        
FileChannel inChannel = 
new
 FileInputStream( in ).getChannel();  

05.
        
FileChannel outChannel = 
new
 FileOutputStream( out ).getChannel();  

06.
        
try
 
07.
        
{  

08.
//         
inChannel.transferTo(0, inChannel.size(), outChannel);      // original
-- apparently has trouble copying large files on Windows  

09.
 
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

01.
private
 void
 createThumbnail(String filename, 
int
 thumbWidth, 
int
 thumbHeight, 
int
 quality, String outFilename)  

02.
        
throws
 InterruptedException, FileNotFoundException, IOException  

03.
    
{  

04.
        
// load image from filename  

05.
        
Image image = Toolkit.getDefaultToolkit().getImage(filename);  

06.
        
MediaTracker mediaTracker = 
new
 MediaTracker(
new
 Container());  

07.
        
mediaTracker.addImage(image, 
0
);  

08.
        
mediaTracker.waitForID(
0
);  

09.
        
// use this to test for errors at this point: System.out.println(mediaTracker.isErrorAny());  

10.
 
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.
        
}  

21.
 
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
);  

28.
 
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

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)

01.
import
 org.json.JSONObject;  

02.
...  

03.
...  

04.
JSONObject json = 
new
 JSONObject();  

05.
json.put(
"city"
, 
"Mumbai"
);  

06.
json.put(
"country"
, 
"India"
);  

07.
...  

08.
String output = json.toString();  

09.
...

10. 使用iText JAR生成PDF

阅读这篇文章了解更多细节

01.
 
02.
import
 java.io.File;  

03.
import
 java.io.FileOutputStream;  

04.
import
 java.io.OutputStream;  

05.
import
 java.util.Date;  

06.
 
07.
import
 com.lowagie.text.Document;  

08.
import
 com.lowagie.text.Paragraph;  

09.
import
 com.lowagie.text.pdf.PdfWriter;  

10.
 
11.
public
 class
 GeneratePDF {  

12.
 
13.
    
public
 static
 void
 main(String[] args) {  

14.
        
try
 {  

15.
            
OutputStream file = 
new
 FileOutputStream(
new
 File(
"C:\\Test.pdf"
));  

16.
 
17.
            
Document document = 
new
 Document();  

18.
            
PdfWriter.getInstance(document, file);  

19.
            
document.open();  

20.
            
document.add(
new
 Paragraph(
"Hello Kiran"
));  

21.
            
document.add(
new
 Paragraph(
new
 Date().toString()));  

22.
 
23.
            
document.close();  

24.
            
file.close();  

25.
 
26.
        
} 
catch
 (Exception e) {  

27.
 
28.
            
e.printStackTrace();  

29.
        
}  

30.
    
}  

31.
}

11. HTTP 代理设置

阅读这篇文章了解更多细节。

1.
 
 


2.
System.getProperties().put(
"http.proxyHost"
, 
"someProxyURL"
);  



3.
System.getProperties().put(
"http.proxyPort"
, 
"someProxyPort"
);  



4.
System.getProperties().put(
"http.proxyUser"
, 
"someUserName"
);  



5.
System.getProperties().put(
"http.proxyPassword"
, 
"somePassword"
); 

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20非常有用的Java程序片段 (中) | 优秀程序员的十个习惯

2009-05-26 14:02
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