下面是20个非常有用的Java程序片段,希望能对你有用。内容比较早,有些函数可能过时了,但是总体思路是不错滴,供参考。
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
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
8、创建图片的缩略图
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) http://viralpatel.net/blogs/download/json/json-rpc-1.0.jar
- 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
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
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 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>
XML文件
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]);
- }
- plain