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 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 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,
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; 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文件
Java代码 package net.viralpatel.java.xmlparser; import java.io.File; 17、把 Array 转换成 Map import java.util.Map; 18、发送邮件 import javax.mail.*; 19、发送代数据的HTTP 请求 import java.io.BufferedReader; 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
作者:陈皓 |
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来自: fishpan_oliver > 《阅读笔记》