程序员精选
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 int2、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 ); log.info("开始处理类目历史数据时间为:{}", DateFormatUtils.format(new Date(), DateFormatUtils.ISO_DATETIME_FORMAT.getPattern()));org.apache.commons.lang3.time
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: est.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")); } }
Arrays的equals方法，比较两个数组是否相同，工具类已经帮封装好，比较的是内部的每一位是否相等，并给出正确答案,即使你运行Arrays.equas(null,null)也不会抛出任何异常(会得出true),而且内部数据会自带拆箱，也就是说Long[] la = {1L, new Long(2), 3L};与 Long[] lb = {1L, 2L, 3L}; 是相等的，Long[] lc = {1L, 2L, 3L,4L};与Long[] ld = {1L, 2L, 3L};是不相等的
Arrays的sort方法，排序方法默认是按照升序排序Arrays.sort(lc)，也可以指定Arrays.sort(lc,Collections.reverseOrder())为倒叙排序，方法没有返回值，会更改数据原结构,但是如果数组是空会抛出空指针异常
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]); }plain21、bean之间的拷贝
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// // Source code recreated from a .class file by IntelliJ IDEA // (powered by Fernflower decompiler) // package com.jd.ecc.commons.lib.utils; import java.util.concurrent.ConcurrentHashMap; import java.util.concurrent.ConcurrentMap; import org.springframework.cglib.beans.BeanCopier; import org.springframework.cglib.core.Converter; public class BeanCopierUtils { private static ConcurrentMap<String, BeanCopier> beanCopierMap = new ConcurrentHashMap(120); public BeanCopierUtils() { } public static void copyProperties(Object source, Object target) { String beanKey = generateKey(source.getClass(), target.getClass()); BeanCopier copier = null; if(!beanCopierMap.containsKey(beanKey)) { copier = BeanCopier.create(source.getClass(), target.getClass(), false); beanCopierMap.put(beanKey, copier); } else { copier = (BeanCopier)beanCopierMap.get(beanKey); } copier.copy(source, target, (Converter)null); } private static String generateKey(Class<?> class1, Class<?> class2) { return class1.toString() + class2.toString(); } }
//会吧null值也考入target中,所有值都会考入target中，但是属性名称缺少不会报错
来自：酷 壳 - CoolShell
链接：http://coolshell.cn/articles/889.html
TWO
package com.jd.ecc.b2b.item.common.utils; import lombok.extern.slf4j.Slf4j; import org.apache.commons.beanutils.PropertyUtils; import org.springframework.beans.BeanUtils; import java.beans.PropertyDescriptor; import java.lang.reflect.InvocationTargetException; import java.util.Arrays; import java.util.Map; import java.util.stream.Collectors; @Slf4j public class BeanUtil { private BeanUtil() { } public static void copy(Object source, Object target) { BeanUtils.copyProperties(source, target); try { PropertyDescriptor[] sfs = BeanUtils.getPropertyDescriptors (source.getClass()); PropertyDescriptor[] tfs = BeanUtils.getPropertyDescriptors (target.getClass()); if(null == sfs || sfs.length < 1) { return; } if(null == sfs || tfs.length < 1) { return; } Map<String, PropertyDescriptor> fms = Arrays.asList (sfs).stream() .collect(Collectors.toMap(PropertyDescriptor::getName, it -> it)); Map<String, PropertyDescriptor> tms = Arrays.asList(tfs).stream () .collect(Collectors.toMap(PropertyDescriptor::getName, it -> it)); fms.forEach((k, v) -> { if(!tms.containsKey(k)) { return; } String sn = v.getPropertyType().getName(); String tn = tms.get(k).getPropertyType().getName(); if(sn.equals(tn)) { return; } Object sv = null; try { sv = PropertyUtils.getProperty(source, k); if(null == sv) { return; } if(tn.contains("Byte")) { PropertyUtils.setProperty(target, k, new Byte (String.valueOf(sv))); return; } if(tn.contains("Integer")) { PropertyUtils.setProperty(target, k, Integer.valueOf (String.valueOf(sv))); return; } if(tn.contains("String")) { PropertyUtils.setProperty(target, k, String.valueOf(sv)); return; } } catch (IllegalAccessException e) { e.printStackTrace(); } catch (InvocationTargetException e) { e.printStackTrace(); } catch (NoSuchMethodException e) { e.printStackTrace(); } }); } catch (Exception e) {
log.error("拷贝名称相同名称，类型不同出错！source:{},target:{},e:{}",source,target,e);
}
THREE:
ConvertUtils.register(new DateConverter(null), java.util.Date.class);//避免时间拷贝出错 BeanUtils.copyProperties(desc, src);
22、数组类型转换
org.apache.commons.beanutils
String[] receivers = receiverIds.split(","); //将校验Id转换为Long类型 Long[] receiverIds = (Long[]) ConvertUtils.convert(receivers,Long.class);
23、数组集合转换
List<Long> listFailIds = new ArrayList<Long>(); Long[] failReceiveIds = new Long[perCount];
failReceiveIds = listFailIds.toArray(new Long[listFailIds.size()]);
24、枚举示例
package com.common.enumtype; /** * @author 2016/8/26. */ public enum MessageStatusEnum { /** * 定向消息消息查询消息状态枚举 */ MESSAGE_STATUS_ALL(0,"全部"), MESSAGE_STATUS_SEND(1,"已发送"), MESSAGE_STATUS_DRAFT(2,"未发送"), MESSAGE_STATUS_EXECUTE(3,"发送中"), MESSAGE_STATUS_PENDING_AUDIT(10,"待审核"); private Integer code; private String type; MessageStatusEnum(Integer code, String type) { this.code = code; this.type = type; } public static MessageStatusEnum getMessageStatusEnumByCode(Integer code) { for (MessageStatusEnum messageStatusEnum : MessageStatusEnum.values()) { if(code != null && code.intValue() == messageStatusEnum.getCode()){ return messageStatusEnum; } } return null; } public Integer getCode() { return code; } public void setCode(Integer code) { this.code = code; } public String getType() { return type; } public void setType(String type) { this.type = type; }
}
25、json数组余集合数组转换
String baseAddresses; List<BaseAddress> addresseList = new ArrayList<>();
JSONArray jsonArray = JSONArray.fromObject(baseAddresses); BaseAddress baseAddress; ObjectMapper objectMapper = new ObjectMapper(); for (int i = 0; i < jsonArray.size(); i++) { try { baseAddress = objectMapper.readValue(jsonArray.getString(i), BaseAddress.class); addresseList.add(baseAddress); } catch (IOException e) { e.printStackTrace(); }
}
import com.fasterxml.jackson.databind.ObjectMapper; import net.sf.json.JSONArray;
26、StringJoiner字符串拼接
StringJoiner sj = new StringJoiner(":", "[", "]"); sj.add("George").add("Sally").add("Fred"); String desiredString = sj.toString();
27、java的图画库平时很少用，下面为一则画图示例
