常用的Java代码汇总
来源:互联网 发布:云计算发展方向 编辑:程序博客网 时间:2024/05/29 08:11
转自:http://www.itjhwd.com/java_code/
1. 字符串有整型的相互转换
Java
1
2
<strong>Stringa =String.valueOf(2); //integer to numeric string
inti =Integer.parseInt(a);//numeric string to an int </strong>
2. 向文件末尾添加内容
Java
1
2
3
4
5
6
7
8
9
10
11
<strong>BufferedWriterout =null;
try{
out= newBufferedWriter(newFileWriter(”filename”,true));
out.write(”aString”);
}catch (IOExceptione){
// error processing code
}finally {
if(out!= null){
out.close();
}
}</strong>
3. 得到当前方法的名字
Java
1
<strong>StringmethodName =Thread.currentThread().getStackTrace()[1].getMethodName(); </strong>
4. 转字符串到日期
Java
1
<strong>java.util.Date= java.text.DateFormat.getDateInstance().parse(dateString); </strong>
或者是:
Java
1
2
<strong>SimpleDateFormatformat =new SimpleDateFormat("dd.MM.yyyy" );
Date date= format.parse(myString ); </strong>
5. 使用JDBC链接Oracle
Java
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
<strong>publicclass OracleJdbcTest
{
StringdriverClass ="oracle.jdbc.driver.OracleDriver";
Connectioncon;
publicvoid init(FileInputStreamfs)throws ClassNotFoundException,SQLException,FileNotFoundException,IOException
{
Propertiesprops =new Properties();
props.load(fs);
Stringurl =props.getProperty("db.url");
StringuserName =props.getProperty("db.user");
Stringpassword =props.getProperty("db.password");
Class.forName(driverClass);
con=DriverManager.getConnection(url,userName,password);
}
publicvoid fetch()throws SQLException,IOException
{
PreparedStatementps =con.prepareStatement("select SYSDATE from dual");
ResultSet rs= ps.executeQuery();
while(rs.next())
{
// do the thing you do
}
rs.close();
ps.close();
}
publicstatic voidmain(String[]args)
{
OracleJdbcTest test =new OracleJdbcTest();
test.init();
test.fetch();
}
} </strong>
6. 把 Java util.Date 转成 sql.Date
Java
1
2
<strong>java.util.DateutilDate =new java.util.Date();
java.sql.DatesqlDate =new java.sql.Date(utilDate.getTime());</strong>
7. 使用NIO进行快速的文件拷贝
Java
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
<strong>publicstatic voidfileCopy(File in,File out)
throwsIOException
{
FileChannel inChannel= newFileInputStream(in ).getChannel();
FileChanneloutChannel =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)
intmaxCount =(64* 1024* 1024)- (32* 1024);
longsize =inChannel.size();
longposition =0;
while( position< size)
{
position+= inChannel.transferTo(position,maxCount,outChannel );
}
}
finally
{
if( inChannel!= null)
{
inChannel.close();
}
if( outChannel!= null)
{
outChannel.close();
}
}
} </strong>
8. 创建图片的缩略图
Java
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
<strong>privatevoid createThumbnail(Stringfilename,int thumbWidth,int thumbHeight,int quality,String outFilename)
throwsInterruptedException,FileNotFoundException,IOException
{
// load image from filename
Imageimage =Toolkit.getDefaultToolkit().getImage(filename);
MediaTracker mediaTracker= newMediaTracker(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
doublethumbRatio =(double)thumbWidth/ (double)thumbHeight;
intimageWidth =image.getWidth(null);
intimageHeight =image.getHeight(null);
doubleimageRatio =(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);
Graphics2Dgraphics2D =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));
JPEGImageEncoderencoder =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();
} </strong>
9.创建 JSON 格式的数据
并下面这个JAR 文件:json-rpc-1.0.jar (75 kb)
Java
1
2
3
4
5
6
7
8
9
<strong>importorg.json.JSONObject;
...
...
JSONObject json= newJSONObject();
json.put("city","Mumbai");
json.put("country","India");
...
Stringoutput =json.toString();
...</strong>
10. 使用iText JAR生成PDF
Java
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
<strong>importjava.io.File;
importjava.io.FileOutputStream;
importjava.io.OutputStream;
importjava.util.Date;
importcom.lowagie.text.Document;
importcom.lowagie.text.Paragraph;
importcom.lowagie.text.pdf.PdfWriter;
publicclass GeneratePDF{
publicstatic voidmain(String[]args){
try{
OutputStream file =new FileOutputStream(newFile("C:\\Test.pdf"));
Document document= newDocument();
PdfWriter.getInstance(document,file);
document.open();
document.add(newParagraph("Hello Kiran"));
document.add(newParagraph(newDate().toString()));
document.close();
file.close();
}catch (Exceptione){
e.printStackTrace();
}
}
} </strong>
11. HTTP 代理设置
Java
1
2
3
4
5
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
Java
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
<strong>
publicclass SimpleSingleton{
privatestatic SimpleSingletonsingleInstance = newSimpleSingleton();
//Marking default constructor private
//to avoid direct instantiation.
privateSimpleSingleton(){
}
//Get instance for class SimpleSingleton
publicstatic SimpleSingletongetInstance(){
returnsingleInstance;
}
} </strong>
另一种实现
Java
1
2
3
4
5
6
7
8
<strong>publicenum SimpleSingleton{
INSTANCE;
publicvoid doSomething(){
}
}
//Call the method from Singleton:
SimpleSingleton.INSTANCE.doSomething(); </strong>
13. 抓屏程序
Java
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
<strong>importjava.awt.Dimension;
importjava.awt.Rectangle;
importjava.awt.Robot;
importjava.awt.Toolkit;
importjava.awt.image.BufferedImage;
importjavax.imageio.ImageIO;
importjava.io.File;
...
publicvoid captureScreen(StringfileName)throws Exception{
DimensionscreenSize =Toolkit.getDefaultToolkit().getScreenSize();
Rectangle screenRectangle= newRectangle(screenSize);
Robotrobot =new Robot();
BufferedImage image= robot.createScreenCapture(screenRectangle);
ImageIO.write(image,"png",new File(fileName));
}
... </strong>
14. 列出文件和目录
Java
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
<strong>Filedir =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
Stringfilename =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= newFilenameFilter(){
publicboolean accept(Filedir,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
FileFilterfileFilter =new FileFilter(){
publicboolean accept(Filefile){
returnfile.isDirectory();
}
};
files= dir.listFiles(fileFilter); </strong>
15. 创建ZIP和JAR文件
Java
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
<strong>
importjava.util.zip.*;
importjava.io.*;
publicclass ZipIt{
publicstatic voidmain(Stringargs[])throws IOException{
if(args.length< 2){
System.err.println("usage: java ZipIt Zip.zip file1 file2 file3");
System.exit(-1);
}
FilezipFile =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);
ZipOutputStreamzos =new ZipOutputStream(fos);
intbytesRead;
byte[]buffer =new byte[1024];
CRC32 crc= newCRC32();
for(inti=1,n=args.length;i <n;i++){
Stringname =args[i];
Filefile =new File(name);
if(!file.exists()){
System.err.println("Skipping: " +name);
continue;
}
BufferedInputStreambis =new BufferedInputStream(
newFileInputStream(file));
crc.reset();
while((bytesRead= bis.read(buffer))!= -1){
crc.update(buffer,0,bytesRead);
}
bis.close();
// Reset to beginning of input stream
bis= newBufferedInputStream(
newFileInputStream(file));
ZipEntry entry= newZipEntry(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();
}
} </strong>
16. 解析/读取XML 文件
XML文件
Java
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
<?xmlversion="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
Java
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
74
packagenet.viralpatel.java.xmlparser;
importjava.io.File;
importjavax.xml.parsers.DocumentBuilder;
importjavax.xml.parsers.DocumentBuilderFactory;
importorg.w3c.dom.Document;
importorg.w3c.dom.Element;
importorg.w3c.dom.Node;
importorg.w3c.dom.NodeList;
publicclass XMLParser{
publicvoid getAllUserNames(StringfileName){
try{
DocumentBuilderFactorydbf =DocumentBuilderFactory.newInstance();
DocumentBuilder db =dbf.newDocumentBuilder();
Filefile =new File(fileName);
if(file.exists()){
Documentdoc =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++){
Nodenode =studentList.item(i);
if(node.getNodeType()== Node.ELEMENT_NODE){
System.out
.println("=====================");
Elemente =(Element)node;
NodeListnodeList =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 (Exceptione){
System.out.println(e);
}
}
publicstatic voidmain(String[]args){
XMLParserparser =new XMLParser();
parser.getAllUserNames("c:\\test.xml");
}
}
17. 把 Array 转换成 Map
Java
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
importjava.util.Map;
importorg.apache.commons.lang.ArrayUtils;
publicclass Main{
publicstatic voidmain(String[]args){
String[][]countries ={ {"United States","New York" },{ "United Kingdom","London" },
{"Netherland","Amsterdam" },{ "Japan","Tokyo" },{ "France","Paris" }};
MapcountryCapitals = 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
Java
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
importjavax.mail.*;
importjavax.mail.internet.*;
importjava.util.*;
publicvoid postMail(String recipients[],String subject,String message, Stringfrom)throws MessagingException
{
booleandebug =false;
//Set the host smtp address
Properties props= newProperties();
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= newMimeMessage(session);
// set the from and to address
InternetAddressaddressFrom =new InternetAddress(from);
msg.setFrom(addressFrom);
InternetAddress[]addressTo =new InternetAddress[recipients.length];
for(inti =0;i <recipients.length;i++)
{
addressTo[i]= newInternetAddress(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
Java
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
importjava.io.BufferedReader;
importjava.io.InputStreamReader;
importjava.net.URL;
publicclass Main{
publicstatic voidmain(String[]args) {
try{
URL my_url= newURL("http://coolshell.cn/");
BufferedReaderbr =new BufferedReader(newInputStreamReader(my_url.openStream()));
StringstrTemp ="";
while(null!= (strTemp= br.readLine())){
System.out.println(strTemp);
}
}catch (Exceptionex){
ex.printStackTrace();
}
}
}
20. 改变数组的大小
Java
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
/**
* 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.
*/
privatestatic ObjectresizeArray (ObjectoldArray,int newSize){
intoldSize =java.lang.reflect.Array.getLength(oldArray);
ClasselementType =oldArray.getClass().getComponentType();
ObjectnewArray =java.lang.reflect.Array.newInstance(
elementType,newSize);
intpreserveLength = Math.min(oldSize,newSize);
if(preserveLength> 0)
System.arraycopy(oldArray,0,newArray,0,preserveLength);
returnnewArray;
}
// Test routine for resizeArray().
publicstatic voidmain (String[]args){
int[]a ={1,2,3};
a= (int[])resizeArray(a,5);
a[3]= 4;
a[4]= 5;
for(inti=0;i<a.length;i++)
System.out.println(a[i]);
}
本文固定链接:http://www.itjhwd.com/java_code/
转载请注明: IT江湖 2014年05月28日 于 IT江湖 发表
0 0
- 常用的Java代码汇总
- 常用的Java代码汇总
- 常用的Java代码汇总
- 常用的Java代码汇总
- 常用的Java代码汇总
- 常用的Java代码汇总
- 常用的Java代码汇总
- 常用的Java代码汇总
- 常用的Java代码汇总
- 常用的Java代码汇总
- 常用的Java代码汇总
- 常用的Java代码汇总
- 常用Java代码汇总
- Java中常用的代码汇总
- 常用的Java基本代码汇总
- Java中常用的代码汇总
- Java常用代码片段汇总
- [JAVA技术] Java中常用的代码汇总
- Flex使用 RemoteObject 组件
- Linux终端使用技巧
- linux配置vncserver服务
- Project 2013项目管理教程(4):设置资源
- 花果山装腔指南
- 常用的Java代码汇总
- UVa 558 - Wormholes(spfa判断负环)
- android 遇到unable to resolve superclass of 类的问题
- poj 2593
- Java算法快速排序
- ARM参数传递
- wine
- 你还在用模拟器测试Android应用吗?OUT了,教你用真机测试(原创)
- 区分Activity的四种加载模式----以及Intent的setFlags