1. 字符串有整型的相互转换?
Java代码?
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?
Java代码?
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.}??
Java代码?
1.
3.?得到当前方法的名字??
2.String?methodName?=?Thread.currentThread().getStackTrace()[1].getMethodName();??
4. 转字符串到日期?
Java代码?
1.java.util.Date?=?java.text.DateFormat.getDateInstance().parse(date?String);??
或者是：?
Java代码?
1.SimpleDateFormat?format?=?new?SimpleDateFormat(?"dd.MM.yyyy"?);????
2.Date?date?=?format.parse(?myString?);??
5. 使用JDBC链接Oracle?
Java代码?
1.public?
class?OracleJdbcTest????
2.{????
3.????String?driverClass?=?"oracle.jdbc.driver.OracleDriver";????
4.??
5.????Connection?con;????
6.??
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);????
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?
Java代码?
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?
Java代码?
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????
9.??
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?
Java代码?
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.get
DefaultToolkit().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());????
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)?
Java代码?
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?
阅读这篇文章?了解更多细节?
Java代码?
1.import?java.io.File;????
2.import?java.io.FileOutputStream;????
3.import?java.io.OutputStream;????
4.import?java.util.Date;????
5.??
6.import?com.lowagie.text.Document;????
7.import?com.lowagie.text.Paragraph;????
8.import?com.lowagie.text.pdf.PdfWriter;????
9.??
10.public?class?GeneratePDF?{????
11.??
12.????public?static?void?main(String[]?args)?{????
13.????????try?{????
14.????????????OutputStream?file?=?new?FileOutputStream(new?File("C:\\Test.pdf"));????
15.??
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()));????
21.??
22.????????????document.close();????
23.????????????file.close();????
24.??
25.????????}?catch?(Exception?e)?{????
26.??
27.????????????e.printStackTrace();????
28.????????}????
29.????}????
30.}??
11.
HTTP 代理设置?
阅读这篇?文章?了解更多细节。?
Java代码?
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?
请先阅读这篇文章?了解更多信息?
Java代码?
1.public?class?SimpleSingleton?{????
2.????private?static?SimpleSingleton?singleInstance?=??new?SimpleSingleton();????
3.??
4.????//Marking?default?constructor?private????
5.????//to?avoid?direct?instantiation.????
6.????private?SimpleSingleton()?{????
7.????}????
8.??
9.????//Get?
instance?for?class?SimpleSingleton????
10.????public?static?SimpleSingleton?getInstance()?{????
11.??
12.????????return?singleInstance;????
13.????}????
14.}??
另一种实现?
Java代码?
1.public?enum?SimpleSingleton?{????
2.????INSTANCE;????
3.????public?void?doSomething()?{????
4.????}????
5.}????
6.??
7.//Call?the?method?from?Singleton:????
8.SimpleSingleton.INSTANCE.doSomething();??
13. 抓屏程序?
阅读这篇文章?获得更多信息。?
Java代码?
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;????
8.??
9....????
10.??
11.public?void?captureScreen(String?fileName)?throws?Exception?{????
12.??
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));????
18.??
19.}????
20....??
14. 列出文件和目录?
Java代码?
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[i];????
9.??????}????
10.??}????
11.??
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);????
20.??
21.??//?The?list?of?files?
can?also?be?retrieved?as?File?objects????
22.??File[]?files?=?dir.listFiles();????
23.??
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);??
15. 创建ZIP和JAR文件?
Java代码?
1.import?java.util.zip.*;????
2.import?java.io.*;????
3.??
4.public?class?ZipIt?{????
5.????public?static?void?main(String?args[])?throws?IOException?{????
6.????????if?(args.length?<?2)?{????
7.????????????System.err.println("usage:?java?ZipIt?Zip.zip?file1?file2?file3");????
8.????????????System.exit(-1);????
9.????????}????
10.????????File?zipFile?=?new?File(args[0]);????
11.????????if?(zipFile.exists())?{????
12.????????????System.err.println("Zip?file?already?exists,?please?try?another");????
13.????????????System.exit(-2);????
14.????????}????
15.????????FileOutputStream?fos?=?new?FileOutputStream(zipFile);????
16.????????ZipOutputStream?zos?=?new?ZipOutputStream(fos);????
17.????????int?bytesRead;????
18.????????byte[]?buffer?=?new?byte[1024];????
19.????????CRC32?crc?=?new?CRC32();????
20.????????for?(int?i=1,?n=args.length;?i?<?n;?i++)?{????
21.????????????String?name?=?args[i];????
22.????????????File?file?=?new?File(name);????
23.????????????if?(!file.exists())?{????
24.????????????????System.err.println("Skipping:?"?+?name);????
25.????????????????
continue;????
26.????????????}????
27.????????????BufferedInputStream?bis?=?new?BufferedInputStream(????
28.????????????????new?FileInputStream(file));????
29.????????????crc.reset();????
30.????????????while?((bytesRead?=?bis.read(buffer))?!=?-1)?{????
31.????????????????crc.update(buffer,?0,?bytesRead);????
32.????????????}????
33.????????????bis.close();????
34.????????????//?Reset?to?beginning?of?input?stream????
35.????????????bis?=?new?BufferedInputStream(????
36.????????????????new?FileInputStream(file));????
37.????????????ZipEntry?entry?=?new?ZipEntry(name);????
38.????????????entry.setMethod(ZipEntry.STORED);????
39.????????????entry.setCompressedSize(file.length());????
40.????????????entry.setSize(file.length());????
41.????????????entry.setCrc(crc.getValue());????
42.????????????zos.putNextEntry(entry);????
43.????????????while?((bytesRead?=?bis.read(buffer))?!=?-1)?{????
44.????????????????zos.write(buffer,?0,?bytesRead);????
45.????????????}????
46.????????????bis.close();????
47.????????}????
48.????????zos.close();????
49.????}????
50.}??
16.
解析/读取
XML 文件?
XML文件?
代码?
1.<?xml?version="1.0"?>???
2.<students>???
3.????<student>???
4.????????<name>John</name>???
5.????????<grade>B</grade>???
6.????????<age>12</age>???
7.????</student>???
8.????<student>???
9.????????<name>Mary</name>???
10.????????<grade>A</grade>???
11.????????<age>11</age>???
12.????</student>???
13.????<student>???
14.????????<name>Simon</name>???
15.????????<grade>A</grade>???
16.????????<age>18</age>???
17.????</student>???
18.</students>??
Java代码?
1.package?net.viralpatel.java.xmlparser;????
2.??
3.import?java.io.File;????
4.import?javax.xml.parsers.DocumentBuilder;????
5.import?javax.xml.parsers.DocumentBuilderFactory;????
6.??
7.import?org.w3c.dom.Document;????
8.import?org.w3c.dom.Element;????
9.import?org.w3c.dom.Node;????
10.import?org.w3c.dom.NodeList;????
11.??
12.public?class?XMLParser?{????
13.??
14.????public?void?getAllUserNames(String?fileName)?{????
15.????????try?{????
16.????????????DocumentBuilderFactory?dbf?=?DocumentBuilderFactory.newInstance();????
17.????????????DocumentBuilder?db?=?dbf.newDocumentBuilder();????
18.????????????File?file?=?new?File(fileName);????
19.????????????if?(file.exists())?{????
20.????????????????Document?doc?=?db.parse(file);????
21.????????????????Element?docEle?=?doc.getDocumentElement();????
22.??
23.????????????????//?Print?root?element?of?the?document????
24.????????????????System.out.println("Root?element?of?the?document:?"???
25.????????????????????????+?docEle.getNodeName());????
26.??
27.????????????????NodeList?studentList?=?docEle.getElementsByTagName("student");????
28.??
29.????????????????//?Print?total?student?elements?in?document????
30.????????????????System.out????
31.????????????????????????.println("Total?students:?"?+?studentList.getLength());????
32.??
33.????????????????if?(studentList?!=?null?&&?studentList.getLength()?>?0)?{????
34.????????????????????for?(int?i?=?0;?i?<?studentList.getLength();?i++)?{????
35.??
36.????????????????????????Node?node?=?studentList.item(i);????
37.??
38.????????????????????????if?(node.getNodeType()?==?Node.ELEMENT_NODE)?{????
39.??
40.????????????????????????????System.out????
41.????????????????????????????????????.println("=====================");????
42.??
43.????????????????????????????Element?e?=?(Element)?node;????
44.????????????????????????????NodeList?nodeList?=?e.getElementsByTagName("name");????
45.????????????????????????????System.out.println("Name:?"???
46.????????????????????????????????????+?nodeList.item(0).getChildNodes().item(0)????
47.????????????????????????????????????????????.getNodeValue());????
48.??
49.????????????????????????????nodeList?=?e.getElementsByTagName("grade");????
50.????????????????????????????System.out.println("Grade:?"???
51.????????????????????????????????????+?nodeList.item(0).getChildNodes().item(0)????
52.????????????????????????????????????????????.getNodeValue());????
53.??
54.????????????????????????????nodeList?=?e.getElementsByTagName("age");????
55.????????????????????????????System.out.println("Age:?"???
56.????????????????????????????????????+?nodeList.item(0).getChildNodes().item(0)????
57.????????????????????????????????????????????.getNodeValue());????
58.????????????????????????}????
59.????????????????????}????
60.????????????????}?else?{????
61.????????????????????System.exit(1);????
62.????????????????}????
63.????????????}????
64.????????}?catch?(Exception?e)?{????
65.????????????System.out.println(e);????
66.????????}????
67.????}????
68.????public?static?void?main(String[]?args)?{????
69.??
70.????????XMLParser?parser?=?new?XMLParser();????
71.????????parser.getAllUserNames("c:\\test.xml");????
72.????}????
73.}??
17. 把 Array 转换成 Map?
Java代码?
1.import?java.util.Map;????
2.import?org.apache.commons.lang.ArrayUtils;????
3.??
4.public?class?Main?{????
5.??
6.??public?static?void?main(String[]?args)?{????
7.????String[][]?countries?=?{?{?"United?States",?"New?York"?},?{?"United?Kingdom",?"London"?},????
8.????????{?"Netherland",?"Amsterdam"?},?{?"Japan",?"Tokyo"?},?{?"France",?"Paris"?}?};????
9.??
10.????Map?countryCapitals?=?ArrayUtils.toMap(countries);????
11.??
12.????System.out.println("Capital?of?Japan?is?"?+?countryCapitals.get("Japan"));????
13.????System.out.println("Capital?of?France?is?"?+?countryCapitals.get("France"));????
14.??}????
15.}??
18.
发送邮件?
Java代码?
1.import?javax.mail.*;????
2.import?javax.mail.
internet.*;????
3.import?java.util.*;????
4.??
5.public?void?postMail(?String?recipients[?],?String?subject,?String?message?,?String?from)?throws?MessagingException????
6.{????
7.????boolean?
debug?=?false;????
8.??
9.?????//Set?the?host?smtp?address????
10.?????Properties?props?=?new?Properties();????
11.?????props.put("mail.smtp.host",?"smtp.example.com");????
12.??
13.????//?create?some?properties?and?get?the?default?Session????
14.????Session?session?=?Session.getDefaultInstance(props,?null);????
15.????session.setDebug(debug);????
16.??
17.????//?create?a?message????
18.????Message?msg?=?new?MimeMessage(session);????
19.??
20.????//?set?the?from?and?to?address????
21.????InternetAddress?addressFrom?=?new?InternetAddress(from);????
22.????msg.setFrom(addressFrom);????
23.??
24.????InternetAddress[]?addressTo?=?new?InternetAddress[recipients.length];????
25.????for?(int?i?=?0;?i?<?recipients.length;?i++)????
26.????{????
27.????????addressTo[i]?=?new?InternetAddress(recipients[i]);????
28.????}????
29.????msg.setRecipients(Message.RecipientType.TO,?addressTo);????
30.??
31.????//?Optional?:?You?can?also?set?your?custom?
headers?in?the?Email?if?you?Want????
32.????msg.addHeader("MyHeaderName",?"myHeaderValue");????
33.??
34.????//?Setting?the?Subject?and?Content?Type????
35.????msg.setSubject(subject);????
36.????msg.setContent(message,?"text/plain");????
37.????Transport.send(msg);????
38.}??
19. 发送代数据的HTTP 请求?
Java代码?
1.import?java.io.BufferedReader;????
2.import?java.io.InputStreamReader;????
3.import?java.net.URL;????
4.??
5.public?class?Main?{????
6.????public?static?void?main(String[]?args)??{????
7.????????try?{????
8.????????????URL?my_url?=?new?URL("http://coolshell.cn/");????
9.????????????BufferedReader?br?=?new?BufferedReader(new?InputStreamReader(my_url.openStream()));????
10.????????????String?strTemp?=?"";????
11.????????????while(null?!=?(strTemp?=?br.readLine())){????
12.????????????System.out.println(strTemp);????
13.????????}????
14.????????}?catch?(Exception?ex)?{????
15.????????????ex.printStackTrace();????
16.????????}????
17.????}????
18.}??
20. 改变数组的大小?
Java代码?
1./**??
2.*?Reallocates?an?array?with?a?new?size,?and?copies?the?contents??
3.*?of?the?old?array?to?the?new?array.??
4.*?@param?oldArray??the?old?array,?to?be?reallocated.??
5.*?@param?newSize???the?new?array?size.??
6.*?@return??????????A?new?array?with?the?same?contents.??
7.*/???
8.private?static?Object?resizeArray?(Object?oldArray,?int?newSize)?{????
9.???int?oldSize?=?java.lang.reflect.Array.getLength(oldArray);????
10.???Class?elementType?=?oldArray.getClass().getComponentType();????
11.???Object?newArray?=?java.lang.reflect.Array.newInstance(????
12.?????????elementType,newSize);????
13.???int?preserveLength?=?Math.min(oldSize,newSize);????
14.???if?(preserveLength?>?0)????
15.??????System.arraycopy?(oldArray,0,newArray,0,preserveLength);????
16.???return?newArray;????
17.}????
18.??
19.//?Test?routine?for?resizeArray().????
20.public?static?void?main?(String[]?args)?{????
21.???int[]?a?=?{1,2,3};????
22.???a?=?(int[])resizeArray(a,5);????
23.???a[3]?=?4;????
24.???a[4]?=?5;????
25.???for?(int?i=0;?i<a.length;?i++)????
26.??????System.out.println?(a[i]);????
27.}??
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