Java程序片段
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 int i = Integer.parseInt(a); //numeric string to an int |
2. 向文件末尾添加内容
1
2
3
4
5
6
7
8
9
10
11
|
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. 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
|
java.util.Date = java.text.DateFormat.getDateInstance().parse(date String); |
或者是:
1
2
|
SimpleDateFormat format = new SimpleDateFormat( "dd.MM.yyyy" ); Date date = format.parse( myString ); |
5. 使用JDBC链接Oracle
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
|
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. 把 Java util.Date 转成 sql.Date
1
2
|
java.util.Date utilDate = new java.util.Date(); java.sql.Date sqlDate = new java.sql.Date(utilDate.getTime()); |
7. 使用NIO进行快速的文件拷贝
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
|
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. 创建图片的缩略图
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
|
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.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(); } |
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)
1
2
3
4
5
6
7
8
9
|
import org.json.JSONObject; ... ... JSONObject json = new JSONObject(); json.put( "city" , "Mumbai" ); json.put( "country" , "India" ); ... String output = json.toString(); ... |
10. 使用iText JAR生成PDF
阅读这篇文章 了解更多细节
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
|
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(); } } } |
11. HTTP 代理设置
阅读这篇 文章 了解更多细节。
1
2
3
4
|
System.getProperties().put( "http.proxyHost" , "someProxyURL" ); System.getProperties().put( "http.proxyPort" , "someProxyPort" ); System.getProperties().put( "http.proxyUser" , "someUserName" ); System.getProperties().put( "http.proxyPassword" , "somePassword" ); |
12. 单实例Singleton 示例
请先阅读这篇文章 了解更多信息
1
2
3
4
5
6
7
8
9
10
11
12
13
14
|
public class SimpleSingleton { private static SimpleSingleton singleInstance = new SimpleSingleton(); //Marking default constructor private //to avoid direct instantiation. private SimpleSingleton() { } //Get instance for class SimpleSingleton public static SimpleSingleton getInstance() { return singleInstance; } } |
另一种实现
1
2
3
4
5
6
7
8
|
public enum SimpleSingleton { INSTANCE; public void doSomething() { } } //Call the method from Singleton: SimpleSingleton.INSTANCE.doSomething(); |
13. 抓屏程序
阅读这篇文章 获得更多信息。
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
|
import java.awt.Dimension; import java.awt.Rectangle; import java.awt.Robot; import java.awt.Toolkit; import java.awt.image.BufferedImage; import javax.imageio.ImageIO; import java.io.File; ... public void captureScreen(String fileName) throws Exception { Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize(); Rectangle screenRectangle = new Rectangle(screenSize); Robot robot = new Robot(); BufferedImage image = robot.createScreenCapture(screenRectangle); ImageIO.write(image, "png" , new File(fileName)); } ... |
14. 列出文件和目录
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
|
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); |
15. 创建ZIP和JAR文件
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
|
import java.util.zip.*; import java.io.*; public class ZipIt { public static void main(String args[]) throws IOException { if (args.length < 2 ) { System.err.println( "usage: java ZipIt Zip.zip file1 file2 file3" ); System.exit(- 1 ); } File zipFile = new File(args[ 0 ]); if (zipFile.exists()) { System.err.println( "Zip file already exists, please try another" ); System.exit(- 2 ); } FileOutputStream fos = new FileOutputStream(zipFile); ZipOutputStream zos = new ZipOutputStream(fos); int bytesRead; byte [] buffer = new byte [ 1024 ]; CRC32 crc = new CRC32(); for ( int i= 1 , n=args.length; i < n; i++) { String name = args[i]; File file = new File(name); if (!file.exists()) { System.err.println( "Skipping: " + name); continue ; } BufferedInputStream bis = new BufferedInputStream( new FileInputStream(file)); crc.reset(); while ((bytesRead = bis.read(buffer)) != - 1 ) { crc.update(buffer, 0 , bytesRead); } bis.close(); // Reset to beginning of input stream bis = new BufferedInputStream( new FileInputStream(file)); ZipEntry entry = new ZipEntry(name); entry.setMethod(ZipEntry.STORED); entry.setCompressedSize(file.length()); entry.setSize(file.length()); entry.setCrc(crc.getValue()); zos.putNextEntry(entry); while ((bytesRead = bis.read(buffer)) != - 1 ) { zos.write(buffer, 0 , bytesRead); } bis.close(); } zos.close(); } } |
16. 解析/读取XML 文件
XML文件
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
|
<?xml version= "1.0" ?> <students> <student> <name>John</name> <grade>B</grade> <age> 12 </age> </student> <student> <name>Mary</name> <grade>A</grade> <age> 11 </age> </student> <student> <name>Simon</name> <grade>A</grade> <age> 18 </age> </student> </students> |
Java代码
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
|
package net.viralpatel.java.xmlparser; import java.io.File; import javax.xml.parsers.DocumentBuilder; import javax.xml.parsers.DocumentBuilderFactory; import org.w3c.dom.Document; import org.w3c.dom.Element; import org.w3c.dom.Node; import org.w3c.dom.NodeList; public class XMLParser { public void getAllUserNames(String fileName) { try { DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance(); DocumentBuilder db = dbf.newDocumentBuilder(); File file = new File(fileName); if (file.exists()) { Document doc = db.parse(file); Element docEle = doc.getDocumentElement(); // Print root element of the document System.out.println( "Root element of the document: " + docEle.getNodeName()); NodeList studentList = docEle.getElementsByTagName( "student" ); // Print total student elements in document System.out .println( "Total students: " + studentList.getLength()); if (studentList != null && studentList.getLength() > 0 ) { for ( int i = 0 ; i < studentList.getLength(); i++) { Node node = studentList.item(i); if (node.getNodeType() == Node.ELEMENT_NODE) { System.out .println( "=====================" ); Element e = (Element) node; NodeList nodeList = e.getElementsByTagName( "name" ); System.out.println( "Name: " + nodeList.item( 0 ).getChildNodes().item( 0 ) .getNodeValue()); nodeList = e.getElementsByTagName( "grade" ); System.out.println( "Grade: " + nodeList.item( 0 ).getChildNodes().item( 0 ) .getNodeValue()); nodeList = e.getElementsByTagName( "age" ); System.out.println( "Age: " + nodeList.item( 0 ).getChildNodes().item( 0 ) .getNodeValue()); } } } else { System.exit( 1 ); } } } catch (Exception e) { System.out.println(e); } } public static void main(String[] args) { XMLParser parser = new XMLParser(); parser.getAllUserNames( "c:\\test.xml" ); } } |
17. 把 Array 转换成 Map
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
|
import java.util.Map; import org.apache.commons.lang.ArrayUtils; public class Main { public static void main(String[] args) { 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" )); } } |
18. 发送邮件
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
|
import javax.mail.*; import javax.mail.internet.*; import java.util.*; public void postMail( String recipients[ ], String subject, String message , String from) throws MessagingException { boolean debug = false ; //Set the host smtp address Properties props = new Properties(); props.put( "mail.smtp.host" , "smtp.example.com" ); // create some properties and get the default Session Session session = Session.getDefaultInstance(props, null ); session.setDebug(debug); // create a message Message msg = new MimeMessage(session); // set the from and to address InternetAddress addressFrom = new InternetAddress(from); msg.setFrom(addressFrom); InternetAddress[] addressTo = new InternetAddress[recipients.length]; for ( int i = 0 ; i < recipients.length; i++) { addressTo[i] = new InternetAddress(recipients[i]); } msg.setRecipients(Message.RecipientType.TO, addressTo); // Optional : You can also set your custom headers in the Email if you Want msg.addHeader( "MyHeaderName" , "myHeaderValue" ); // Setting the Subject and Content Type msg.setSubject(subject); msg.setContent(message, "text/plain" ); Transport.send(msg); } |
19. 发送代数据的HTTP 请求
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
|
import java.io.BufferedReader; import java.io.InputStreamReader; import java.net.URL; public class Main { public static void main(String[] args) { try { 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(); } } } |
20. 改变数组的大小
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
|
/** * Reallocates an array with a new size, and copies the contents * of the old array to the new array. * @param oldArray the old array, to be reallocated. * @param newSize the new array size. * @return A new array with the same contents. */ private static Object resizeArray (Object oldArray, int newSize) { int oldSize = java.lang.reflect.Array.getLength(oldArray); Class elementType = oldArray.getClass().getComponentType(); Object newArray = java.lang.reflect.Array.newInstance( elementType,newSize); int preserveLength = Math.min(oldSize,newSize); if (preserveLength > 0 ) System.arraycopy (oldArray, 0 ,newArray, 0 ,preserveLength); return newArray; } // Test routine for resizeArray(). public static void main (String[] args) { int [] a = { 1 , 2 , 3 }; a = ( int [])resizeArray(a, 5 ); a[ 3 ] = 4 ; a[ 4 ] = 5 ; for ( int i= 0 ; i<a.length; i++) System.out.println (a[i]); } |
Java程序片段的更多相关文章
- 20个非常有用的Java程序片段
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 String a = String.valueOf(2); //integer to numeric strin ...
- 整理:20个非常有用的Java程序片段
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 String a = String.valueOf(2); //integer to numeric strin ...
- 收集的20个非常有用的Java程序片段
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 String a = String.valueOf(2); //integer to numeric strin ...
- 20个非常有用的Java程序片段--转
原文地址:http://geek.csdn.net/news/detail/236591 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 String a = ...
- 常用Java程序片段
1.改变数组的大小 package com.js.ai.modules.jsa.test; public class Testxf { private static Object resizeArra ...
- 阿里P7整理20个非常有用的Java程序片段,你知道吗?
1.字符串有整型的相互转换 String a = String.valueOf(2); //integer to numeric string int i = Integer.parseInt( ...
- 非常有用的Java程序片段
1.向文件末尾添加内容 BufferedWriter out = null; try { out = new BufferedWriter(new FileWriter(”filename”, tru ...
- 使用Java程序片段动态生成表格
<% String[] bookName = { "javaweb典型模块大全", "java从入门到放弃", "C语言程序设计" } ...
- 【分享】20个非常有用的Java程序片段
福利来啦!!! 刚看到的一篇好东东,分享给大家,这些代码留着哦,以后会用得着的... 原文地址:http://developer.51cto.com/art/201306/398347.htm 1. ...
随机推荐
- ABP 初探 之 多语言
最近几天空闲时间比较多,就研究Abp的多语言,Abp是基于接口的依赖注入,有很多思想与方法都很好,需自己深入体会与应用,转化成自己的思想应用于实践. 本篇介绍基于 开源Demo ModuleZeroS ...
- jquery和css3实现滑动导航菜单
效果预览:http://keleyi.com/keleyi/phtml/html5/15/ 有都中颜色可供选择,请使用支持HTML5/CSS3的浏览器访问. HTML源代码: <!DOCTYPE ...
- 64位win7+vs2010编译.net3.5以前的版本问题
一般编译会出现 1.“ResGen.exe”已退出,代码为2 问题处理 2.“错误 2 “LC.exe”已退出,代码为 -1. NBGIS.MainGIS” 3.“未能加载文件或程序集“ESRI.Ar ...
- HIVE 在执行大量数据JOIN的时候,容易产生内存不足的情况
情况 很多时间遇到 "Caused by: java.lang.OutOfMemoryError: Java heap space" Caused by: java.lang.Ou ...
- 【Swift 2.1】共享文件操作小结(iOS 8 +)
前言 适用于 iOS 8 + 本地共享文件列表 声明 欢迎转载,但请保留文章原始出处:) 博客园:http://www.cnblogs.com 农民伯伯: http://over140.cnblogs ...
- Android Touch事件分发机制学习
Android 事件分发机制 ViewGroup dispatchTouchEvent 返回true dispatchTouchEvent: Activity ACTION_DOWN Myrelat ...
- IOS开发之Bug--关于UIImageView的使用
这里是遇到的一个关于使用UIImageView的小bug,bug就是加载不出来图片. 原因:如果图片资源是jpg文件,如果代码没有加后缀.jpg就会出现不加载出来的情况: 添加上.jpg就能加载出来了 ...
- 创建版本库-GIT
什么是版本库呢?版本库又名仓库,英文名repository,你可以简单理解成一个目录,这个目录里面的所有文件都可以被Git管理起来,每个文件的修改.删除,Git都能跟踪,以便任何时刻都可以追踪历史,或 ...
- ORA-27125: unable to create shared memory segment
平台环境 : Oracle Linux Server release 5.7 x86_64 数据库版本 : Oracle Database 10g Enterprise Edition Rel ...
- Linux No volume control GStreamer plugins and/or devices found
案例环境:Oracle Linux Server release 5.7 进入Oracle Linux系统后,在右上角点击声音图标时,则会弹出如下报错窗口: The volume control di ...