20个非常有用的Java程序片段
20个非常有用的Java程序片段
来源:码农网 时间:2015-03-17 10:23:28 阅读数:1057
[导读] 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 string int i = Integer parseInt(a); numeric stri
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 string
int
i = Integer.parseInt(a);
//numeric string to an int
2. 向文件末尾添加内容
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
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
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
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
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
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)
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
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。
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
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
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。
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
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
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
<?
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
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
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
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
import
java.io.BufferedReader;
import
java.io.InputStreamReader;
import
java.net.URL;
public
class
Main {
public
static
void
main(String[] args) {
try
{
URL my_url =
new
URL(
"http://coolshell.cn/"
);
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
/**
* 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]);
}
20个非常有用的Java程序片段相关推荐
- 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 = ...
- 20非常有用的Java程序片段(1)
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 str ...
- 20非常有用的Java程序片段(11-15)
11. HTTP 代理设置 阅读这篇 文章 了解更多细节. 1 2 3 4 5 System.getProperties().put("http.proxyHost", " ...
- 20非常有用的Java程序片段(3)
15. 创建ZIP和JAR文件 import java.util.zip.*; import java.io.*; publicclass ZipIt { publicstaticvoid main( ...
- java 程序片段_20个非常有用的Java程序片段
1. 字符串有整型的相互转换 Java代码 String a = String.valueOf(2); //integer to numeric string int i = Integer.pa ...
- 应用Java程序片段动态生成表格
通过Jsp页面动态来显示数据库中的数据,在根据条件进行查询时,将调查结果显示在jsp页面中,使用java程序片段(Scriptlet)动态生成表格 在jsp文件中,可以在"<%&quo ...
- 分享非常有用的Java程序(关键代码)(七)---抓屏程序
原文:分享非常有用的Java程序(关键代码)(七)---抓屏程序 import java.awt.Dimension; import java.awt.Rectangle; import java.a ...
- 一种基于DFA算法的敏感词检测JAVA程序片段
本文章提供一种基于DFA算法的敏感词检测JAVA程序片段,如下: 1.构造多叉树数据结构 import org.jetbrains.annotations.NotNull;/*** 多叉树* @aut ...
- 应用Java程序片段动态生成下拉列表
从数据库读取数据是,需要将某些数据动态添加到下拉列表中 在下拉列表的选项中,应用的是Java表达式标记输出的数组元素,Java表达式的标记为"<%="和"%> ...
最新文章
- 通信工程和计算机科学会议,计算机科学论坛--2019年IEEE第二届国际计算机与通信工程技术会议(CCET 2019)...
- 解决Sqlite UTF-8中文数据格式在DOS窗口下中文乱码
- Seam开发环境的搭建
- 基于matlab水轮机期刊,基于MATLAB/SIMULINK的水轮机调节系统寻优
- vbe6ext.olb不能被加载解决方案
- java jsonobject转List_java – 将JSONObject转换为List或JSONArray的简单代码?
- java输出二进制数_Java打印整数的二进制表示(代码与解析)
- python编写ftp客户端_用Python写FTP客户端程序
- Android推送通知指南(转)
- JS基础_JS基础语法
- 移动支付--银联,支付宝,微信(android)
- http协议、cookie与session介绍
- [争什么! 掺在一起做撒尿牛丸啊! 笨蛋]ASP.NET Core 2.0 + EF6 + Linux +MySql混搭
- lincese oracle_关于Oracle数据库企业版的license价格
- win10msdn我告诉你哪个版本好
- [高项]工作绩效数据 vs工作绩效信息 vs工作绩效报告
- 前端人脸识别解决方案
- 目前主流游戏引擎的分析报告
- iCloud如何只清理本地缓存而不删除云端文件
- 非真,亦非假——20世纪数学悖论入侵机器学习
热门文章
- 元气骑士机器人修好后怎么用_《元气骑士》五大“难度”挑战,从手速到恶搞很嗨,还能解锁皮肤...
- HDLBits 系列(3)Priority Encoder(Case/Casez)
- shell脚本--猜数字
- Python 全栈开发 -- 开发环境篇
- C++ VS2010 检测到“_ITERATOR_DEBUG_LEVEL”的不匹配项
- 趋势科技4月移动client病毒报告
- JavaScript 的垃圾回收与内存泄露
- Android中SQLite的使用
- 64xWin7Orcale安装
- 最强杀毒软件NOD32免费升级ID(保持最新)