案例一：对QQ号进行验证

  要求：必须是0-15位，0不能开头，只能是数字

在没学过正则表达式，首先想到的是：

public static void check()    {        String qq="0123019";        int len = qq.length();        if(len>=5&&len<=15)        {            if(!qq.startsWith("0"))            {                char[] arr= qq.toCharArray();                boolean flag = true;                for(int x=0;x
     
      ='0'&&arr[x]<=9)                    {                        flag=false;                    }                }                if(flag)                {                    System.out.println("QQ:"+qq);                }                else{                    System.out.println("出现非法字符");                }            }            else{                System.out.println("不可以以0开头");            }        }        else{            System.out.println("小于5或者大于15");        }            }
     

再优化一下，可以这么写：

public static void check()    {        String qq="0123019";        int len = qq.length();        if(len>=5&&len<=15)        {            if(!qq.startsWith("0"))            {                   try {                long l = Long.parseLong(qq);                } catch (NumberFormatException e) {                // TODO Auto-generated catch block                System.out.println("数字异常");                //e.printStackTrace();                }             }            else{                System.out.println("不可以以0开头");            }        }        else{            System.out.println("小于5或者大于15");        }        }}

接下来，最重要，简便的正则表达式派上用场：

public static void regeCheck()    {        String qq = "012345";        String rege = "[1-9][0-9]{4,14}";        //【1-9】代表第一位只能是1-9的数字        //【0-9】{4，14}表示后边是0-0的数字，并且是在4-14位之间        boolean flag = qq.matches(rege);        System.out.println(flag);        if(flag){            System.out.println(qq+"  is OK");        }        else{            System.out.println(qq+"  is error!");        }        }

 

public static void getMails()    {        //System.out.println("getMails");        try {            URL url = new URL("https://mail.qq.com/cgi-bin/frame_html?sid=tSk9WTbKfPKOCCVy&r=0cf16a3eabaaac83f3df241863066baf");            URLConnection conn = null;            try {                conn = url.openConnection();                System.out.println("getMails");            } catch (IOException e1) {                // TODO Auto-generated catch block                e1.printStackTrace();            }            BufferedReader bufIn = null;            try {                bufIn = new BufferedReader(                        new InputStreamReader(conn.getInputStream()));            } catch (IOException e1) {                // TODO Auto-generated catch block                e1.printStackTrace();            }            String line = null;            //String mailreg = "\\w+@\\w+(\\.\\w)+";            String mailreg ="[\\d.][\\d]";            Pattern p = Pattern.compile(mailreg);            try {                while((line=bufIn.readLine())!=null)                {  //System.out.println("oks");                    Matcher m = p.matcher(line);                    //System.out.println(line);                    while(m.find())                    {  System.out.println("getMails");                        System.out.println(m.group());                    }                }            } catch (IOException e) {                // TODO Auto-generated catch block                e.printStackTrace();            }        } catch (MalformedURLException e) {            // TODO Auto-generated catch block            e.printStackTrace();        }            }

•  正则表达式（替换）

//这是函数，将字符串，规则，和替换的新字符串传入执行 public static void repReplace(String str,String reg,String newstr)     {         str = str.replaceAll(reg,newstr);         System.out.println(str);     }

String str = "saee1213edfe32fdsfeeeewfersa1232434";         //1.连续三个数字就替换成#         repReplace(str,"\\d{3,}","#");          //2.将叠词替换成(固定字符)&         repReplace(str,"(.)\\1+","&");         //3.将叠词替换成原来的一个字符 例如 qqq--q;         repReplace(str,"(.)\\1+","$1");

• 正则表达式（获取）

作用：将字符串中符合规则的字符串取出

步骤：1.将正则表达式封装成对象   Pattern

         2.让正则对象和要操作的字符相关联 

         3.关联后，获取正则匹配引擎

　　　 4.通过引擎对符合规则的子串进行操作，比如取出。

 

爬虫，获取网页的信息

package Reptile;import java.io.File;import java.io.FileNotFoundException;import java.io.IOException;import java.io.PrintWriter;import java.util.HashSet;import java.util.Set;import org.jsoup.Jsoup;import org.jsoup.nodes.Document;import org.jsoup.nodes.Element;import org.jsoup.select.Elements;public class JsoupDownloader {     public static final String DEFAULT_SAVE_DIR = "D:/download/";        private static JsoupDownloader downloader;        private JsoupDownloader() {        }        public static JsoupDownloader getInstance() {            if (downloader == null) {                synchronized (JsoupDownloader.class) {                    if (downloader == null) {                        downloader = new JsoupDownloader();                    }                }            }            return downloader;        }        public Document downloadPage(String url) {            try {                System.out.println("正在下载" + url);                return Jsoup.connect(url).get();            } catch (IOException e) {                e.printStackTrace();            }            return null;        }        public Set
     
       parsePage(Document doc, String regex) {            Set
      
        urlSet = new HashSet<>();            if (doc != null) {                Elements elements = doc.select("a[href]");                for (Element element : elements) {                    String url = element.attr("href");                    if (url.length() > 6 && !urlSet.contains(url)) {                        System.out.println(url);                                                if (regex != null && !url.matches(regex)) {                            continue;                        }                        urlSet.add(url);                    }                }            }            return urlSet;        }        public void savePage(Document doc, String saveDir, String saveName, String regex) {            if (doc == null) {                return;            }            if (regex != null && doc.baseUri() != null && !doc.baseUri().matches(regex)) {                return;            }            saveDir = saveDir == null ? DEFAULT_SAVE_DIR : saveDir;            saveName = saveName == null ? doc.title().trim().replaceAll("[\\?/:\\*|<>\" ]", "_") + System.nanoTime() + ".html" : saveName;            File file = new File(saveDir + "/" + saveName);            File dir = file.getParentFile();            if (!dir.exists()) {                dir.mkdirs();            }            PrintWriter printWriter;            try {                printWriter = new PrintWriter(file);                 printWriter.write(doc.toString());                printWriter.close();            } catch (FileNotFoundException e) {                e.printStackTrace();            }        }}
      
     

package Reptile;import java.util.*;public class UrlQueue {     private Set
     
       visitedSet;// 用来存放已经访问过多url        private LinkedList
      
        unvisitedList;// 用来存放未访问过多url        public UrlQueue(String[] seeds) {            visitedSet = new HashSet<>();            unvisitedList = new LinkedList<>();            unvisitedList.addAll(Arrays.asList(seeds));        }        /**         * 添加url         *          * @param url         */        public void enQueue(String url) {            if (url != null && !visitedSet.contains(url)) {                unvisitedList.addLast(url);            }        }        /**         * 添加url         *          * @param urls         */        public void enQueue(Collection
       
         urls) {            for (String url : urls) {                enQueue(url);            }        }        /**         * 取出url         *          * @return         */        public String deQueue() {            try {                String url = unvisitedList.removeFirst();                while(visitedSet.contains(url)) {                    url = unvisitedList.removeFirst();                }                visitedSet.add(url);                return url;            } catch (NoSuchElementException e) {                System.err.println("URL取光了");            }            return null;        }        /**         * 得到已经请求过的url的数目         *          * @return         */        public int getVisitedCount() {            return visitedSet.size();        }}
       
      
     

package Reptile;import java.util.*;import org.jsoup.*;import org.jsoup.Jsoup;import java.util.Set;import org.jsoup.nodes.Document;public class Main {     public static void main(String[] args) {         //StartUrl("http://www.cnblogs.com/artech/");         //StartUrl("http://www.innocellence.com/d/en/");        // String reg = "\\w*\\:\\/\\/\\w*\\.\\w*\\.\\w*\\/";         //StartUrl("http://www.stats.dl.gov.cn","[\\?/:\\*|<>\" ]");         //StartUrl("http://www.innocellence.com","[\\?/:\\*|<>\" ]");        // String s = getUrlList("http://www.innocellence.com");         String str = "saee1213edfe32fdsfeeeewfersa1232434";         //1.连续三个数字就替换成#         repReplace(str,"\\d{3,}","#");          //2.将叠词替换成(固定字符)&         repReplace(str,"(.)\\1+","&");         //3.将叠词替换成原来的一个字符 例如 qqq--q;         repReplace(str,"(.)\\1+","$1");     }     public static void repReplace(String str,String reg,String newstr)     {         str = str.replaceAll(reg,newstr);         System.out.println(str);     }          public static String getUrlList(String str)     {          String s = "Start";     UrlQueue urlQueue = new UrlQueue(new String[]{str});     JsoupDownloader downloader = JsoupDownloader.getInstance();     long start = System.currentTimeMillis();     while (urlQueue.getVisitedCount() < 5) {         String url = urlQueue.deQueue();         System.out.println(url);          //s=url;         // return url;         if (url == null) {             break;         }         Document doc = downloader.downloadPage(url);         if (doc == null) {             continue;         }         Set
     
       urlSet = downloader.parsePage(doc,"\\w*");         urlQueue.enQueue(urlSet);        // downloader.savePage(doc, "C:\\Users\\JiangJianMing\\Desktop\\Test\\", null, "\\w*");                // System.out.println("已请求" + urlQueue.getVisitedCount() + "个页面");         }       return s;     }     public static void StartUrl(String str,String reg)     {            UrlQueue urlQueue = new UrlQueue(new String[]{str});            JsoupDownloader downloader = JsoupDownloader.getInstance();            long start = System.currentTimeMillis();            while (urlQueue.getVisitedCount() < 5) {                String url = urlQueue.deQueue();                System.out.println(str+url);                if (url == null) {                    break;                }                Document doc = downloader.downloadPage(url);                if (doc == null) {                    continue;                }              //  Set
      
        urlSet = downloader.parsePage(doc, "(http://www.cnblogs.com/artech/p|http://www.cnblogs.com/artech/default|http://www.cnblogs.com/artech/archive/\\d{0}/\\d{2}/\\d{2}/).*");               // urlQueue.enQueue(urlSet);              //  downloader.savePage(doc, "C:\\Users\\JiangJianMing\\Desktop\\Test\\", null, "(http://www.cnblogs.com/artech/p|http://www.cnblogs.com/artech/default|http://www.cnblogs.com/artech/archive/\\d{0}/\\d{2}/\\d{2}/).*");                Set
       
         urlSet = downloader.parsePage(doc,reg);                urlQueue.enQueue(urlSet);                downloader.savePage(doc, "C:\\Users\\JiangJianMing\\Desktop\\Test\\", null, reg);                               System.out.println("已请求" + urlQueue.getVisitedCount() + "个页面");            }            long end = System.currentTimeMillis();            System.out.println(">>>>>>>>>>抓去完成，共抓取" + urlQueue.getVisitedCount() + "到个页面，用时" + ((end - start) / 1000) + "s<<<<<<<<<<<<");     }}
       
      
     

•  java连接oracle数据库

            java连接oracle数据库大概可以分为以下几个步骤，在做这些步骤之前，我们需要引入jar包，点击项目，鼠标右键-》Properties，在弹出窗口中，点击左侧的Java Build Path， 在右侧选项卡选择Libraries,再再右侧的按钮中点击Add External JARs...然后选择jar包，如果安装了oracle数据库的话，默认我的在D:\Program\Oracle\product\11.2.0\dbhome_1\jdbc\lib下的ojdbc5.jar这样，就可以开始我们代码的编写了

import java.sql.Connection;import java.sql.DriverManager;import java.sql.ResultSet;import java.sql.SQLException;import java.sql.Statement;public class Link {    public static void main(String[] args) {                //1.加载驱动        try {            Class.forName("oracle.jdbc.driver.OracleDriver");        } catch (ClassNotFoundException e) {            // TODO Auto-generated catch block            e.printStackTrace();        }        try {            //2.得到连接            Connection ct = DriverManager.getConnection("jdbc:oracle:thin:@127.0.0.1:1521:orcl","scott","tiger");            Statement sm = ct.createStatement();            ResultSet rs = sm.executeQuery("select * from emp");             while(rs.next())             {                   System.out.println(rs.getString(1));                                        }        } catch (SQLException e) {            // TODO Auto-generated catch block            e.printStackTrace();        }    }}