20個非常有用的Java程序片段
下面是20個非常有用的Java程序片段，希望能對你有用。內容比較早，有些函數可能過時了，但是總體思路是不錯滴，供參考。
1、字符串有整型的相互轉換
String a = String.valueOf(2); //integer to numeric string
int i = Integer.parseInt(a); //numeric string to an int
2、向文件末尾添加內容
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、得到當前方法的名字
String methodName = Thread.currentThread().getStackTrace()[1].getMethodName();
4、轉字符串到日期
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("開始處理類目歷史數據時間爲:{}", DateFormatUtils.format(new Date(), DateFormatUtils.ISO_DATETIME_FORMAT.getPattern()));org.apache.commons.lang3.time
5、使用JDBC鏈接Oracle
6、把 Java util.Date 轉成 sql.Date
java.util.Date utilDate = new java.util.Date(); java.sql.Date sqlDate = new java.sql.Date(utilDate.getTime());
7、使用NIO進行快速的文件拷貝
8、創建圖片的縮略圖
9、創建 JSON 格式的數據
請先閱讀這篇文章 瞭解一些細節，
並下面這個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
閱讀這篇文章 瞭解更多細節
11、HTTP 代理設置
閱讀這篇 文章 瞭解更多細節。
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、單實例Singleton 示例
請先閱讀這篇文章 瞭解更多信息
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; } }
另一種實現
public enum SimpleSingleton { INSTANCE; public void doSomething() { } } //Call the method from Singleton: SimpleSingleton.INSTANCE.doSomething();
13、抓屏程序
閱讀這篇文章 獲得更多信息。
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、列出文件和目錄
15、創建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/讀取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代碼
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 轉換成 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，比較兩個數組是否相同，工具類已經幫封裝好，比較的是內部的每一位是否相等，並給出正確答案,即使你運行Arrays.equas(null,null)也不會拋出任何異常(會得出true),而且內部數據會自帶拆箱，也就是說Long[] la = {1L, new Long(2), 3L};與 Long[] lb = {1L, 2L, 3L}; 是相等的，Long[] lc = {1L, 2L, 3L,4L};與Long[] ld = {1L, 2L, 3L};是不相等的
Arrays的sort方法，排序方法默認是按照升序排序Arrays.sort(lc)，也可以指定Arrays.sort(lc,Collections.reverseOrder())爲倒敘排序，方法沒有返回值，會更改數據原結構,但是如果數組是空會拋出空指針異常
18、發送郵件
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、發送代數據的HTTP 請求
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、改變數組的大小
/** * 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
21、bean之間的拷貝
O
//
// 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();
}
}
//會吧null值也考入target中,所有值都會考入target中，但是屬性名稱缺少不會報錯
-
來自：酷 殼 - CoolShell
-
鏈接：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("拷貝名稱相同名稱，類型不同出錯！source:{},target:{},e:{}",source,target,e);
}
THREE:
ConvertUtils.register(new DateConverter(null), java.util.Date.class);//避免時間拷貝出錯
BeanUtils.copyProperties(desc, src);
22、數組類型轉換
org.apache.commons.beanutils
String[] receivers = receiverIds.split(",");
//將校驗Id轉換爲Long類型
Long[] receiverIds = (Long[]) ConvertUtils.convert(receivers,Long.class);
23、數組集合轉換
List<Long> listFailIds = new ArrayList<Long>();
Long[] failReceiveIds = new Long[perCount];
failReceiveIds = listFailIds.toArray(new Long[listFailIds.size()]);
24、枚舉示例
package com.common.enumtype;
/**
* @author 2016/8/26.
*/
public enum MessageStatusEnum {
/**
* 定向消息消息查詢消息狀態枚舉
*/
MESSAGE_STATUS_ALL(0,"全部"),
MESSAGE_STATUS_SEND(1,"已發送"),
MESSAGE_STATUS_DRAFT(2,"未發送"),
MESSAGE_STATUS_EXECUTE(3,"發送中"),
MESSAGE_STATUS_PENDING_AUDIT(10,"待審覈");
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數組餘集合數組轉換
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的圖畫庫平時很少用，下面爲一則畫圖示例
