本文给大家分享了20个常用的java代码，都是别人项目中使用过的代码，这里推荐给大家，有需要的小伙伴可以参考下.
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(a); //numeric string to an int
2. 向文件末尾添加内容
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BufferedWriter out = null`;`
try`{`
out = new`BufferedWriter(newFileWriter(”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
String methodName = Thread.currentThread().getStackTrace()[1].getMethodName();
4. 转字符串到日期
java.util.Date = java.text.DateFormat.getDateInstance().parse(date String); 或者是： SimpleDateFormat format = new SimpleDateFormat( “dd.MM.yyyy” ); Date date = format.parse( myString );
5. 使用JDBC链接Oracle
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public`classOracleJdbcTest`
{
String driverClass = "oracle.jdbc.driver.OracleDriver"`;`
Connection con;
public`voidinit(FileInputStream fs)` `throwsClassNotFoundException, 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`voidfetch()` `throwsSQLException, 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`staticvoidmain(String[] args)`
{
OracleJdbcTest test = new`OracleJdbcTest();`
test.init();
test.fetch();
}
}
6. 把 Java util.Date 转成 sql.Date
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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
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public`staticvoidfileCopy( 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 = (6410241024) - (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
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private`voidcreateThumbnail(String filename,` `intthumbWidth,intthumbHeight,` `intquality, String outFilename)`
throws`InterruptedException, FileNotFoundException, IOException`
{
// load image from filename
Image image = Toolkit.getDefaultToolkit().getImage(filename);
MediaTracker mediaTracker = new`MediaTracker(newContainer());`
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(newFileOutputStream(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
并下面这个JAR 文件：json-rpc-1.0.jar (75 kb)/http://t.cn/Rz0bhUA
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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
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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`classGeneratePDF {`
public`staticvoidmain(String[] args) {`
try`{`
OutputStream file = new`FileOutputStream(newFile("C:\\Test.pdf"));`
Document document = new`Document();`
PdfWriter.getInstance(document, file);
document.open();
document.add(`newParagraph(“Hello Kiran”));`
document.add(`newParagraph(newDate().toString()));`
document.close();
file.close();
} catch`(Exception e) {`
e.printStackTrace();
}
}
}
11. HTTP 代理设置
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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
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public`classSimpleSingleton {`
private`staticSimpleSingleton singleInstance =` `newSimpleSingleton();`
//Marking default constructor private
//to avoid direct instantiation.
private`SimpleSingleton() {`
}
//Get instance for class SimpleSingleton
public`staticSimpleSingleton getInstance() {`
return`singleInstance;`
}
}
13. 抓屏程序
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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`voidcaptureScreen(String fileName)` `throwsException {`
Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();
Rectangle screenRectangle = new`Rectangle(screenSize);`
Robot robot = new`Robot();`
BufferedImage image = robot.createScreenCapture(screenRectangle);
ImageIO.write(image, "png"`,newFile(fileName));`
}
...
14. 列出文件和目录
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File dir = new`File("directoryName");`
String[] children = dir.list();
if`(children ==null) {`
// Either dir does not exist or is not a directory
} else`{`
for`(inti=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`booleanaccept(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`booleanaccept(File file) {`
return`file.isDirectory();`
}
};
files = dir.listFiles(fileFilter);
15. 创建ZIP和JAR文件
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import`java.util.zip.*;`
import`java.io.*;`
public`classZipIt {`
public`staticvoidmain(String args[])throwsIOException {`
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 =newbyte[1024];`
CRC32 crc = new`CRC32();`
for`(inti=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
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<?xml version=`“1.0”?>`
<students>
<student>
<name>John</name>
<grade>B</grade>
<age>`12`
</student>
<student>
<name>Mary</name>
<grade>A</grade>
<age>`11`
</student>
<student>
<name>Simon</name>
<grade>A</grade>
<age>`18`
</student>
</students>
Java代码
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<span style=`“font-family:Arial;font-size:14px;”>packagenet.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`classXMLParser {`
public`voidgetAllUserNames(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`(inti =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`staticvoidmain(String[] args) {`
XMLParser parser = new`XMLParser();`
parser.getAllUserNames(`“c:\test.xml”);`
}
}
17. 把 Array 转换成 Map
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import`java.util.Map;`
import`org.apache.commons.lang.ArrayUtils;`
public`classMain {`
public`staticvoidmain(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
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import`javax.mail.*;`
import`javax.mail.internet.*;`
import`java.util.*;`
public`voidpostMail( String recipients[ ], String subject, String message , String from)` `throwsMessagingException`
{
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`(inti =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
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import`java.io.BufferedReader;`
import`java.io.InputStreamReader;`
import`java.net.URL;`
public`classMain {`
public`staticvoidmain(String[] args) {`
try`{`
URL my_url = new`URL("[http://coolshell.cn/](http://coolshell.cn/)");`
BufferedReader br = new`BufferedReader(newInputStreamReader(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
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/**
* 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);`
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`return` `newArray;`
}
// Test routine for resizeArray().
`public` `static` `void` `main (String[] args) {`
|
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`for` `(``int` `i=``0``; i<a.length; i++)`
`System.out.println (a[i]);`
}
以上所述就是本文的全部内容了，希望大家能够喜欢。
摘自：脚本之家
