Java Regular expressions simple to use and web crawler Production Code _java

A regular expression is a rule that is specifically used to manipulate strings.

1. In the string class there are methods for matching strings, cutting.

Determines whether the string matches the given regular expression: Boolean matches (string regex);

To cut a string according to a given regular expression: string[] Split (string regex);

Replace the string that matches the regular expression with the other string we want: String ReplaceAll (string regex,string replacement)

2. Here are some common uses of regular expressions

(1)

Copy Code code as follows:

String regex= "[1-9][0-9]{4,15}";
[1-9] Indicates that this number can only be selected within 1-9
[0-9] means that this number can be 0-9
{4,15} represents a number in this format before it can be repeated 4-15 times

This regular expression means that the first number should be any one in 1-9, and then it must be followed by one of the numbers in 0-9, and that number must appear at least 4 times, at most 15 times.

Such as:

10175 in line

10 does not conform, because [0-9]{4,15}, should appear at least 4 times, here only appears once

(2)

[A-za-z0-9_] {6} represents a character that happens to occur 6 times A-Z or a-Z or _

+ indicates that at least one occurrence

* indicates that 0 or more times have occurred

？ To show one or 0 times

(3) cutting strings according to regular expressions

Copy Code code as follows:

String str= "SJD.KSDJ.SKDJF";

String regex= "\.";

Attention:. In a regular expression is a table-type arbitrary character, a special symbol. We want to use. To cut, we have to convert it to ordinary characters with \ can.

Because \ is also a special symbol, so you need two \ to represent. When we want to use ordinary \, then we should use \\\\ to express.

String[] Ss=str.split (regex); Returns an array of strings: "SJD" "Ksdj" "SKDJF" implements the cutting of an existing string

(4) Replace what we want to replace according to the regular expression

Replaces all occurrences of 5 or more numeric strings in a string with a #

Copy Code code as follows:

String str= "ABCD1334546LASJDFLDSF2343424SDJ";

String regex= "[0-9]{5,}";

String Newstr=str.replaceall (Regex, "#");

(5) Get a string that matches the regular expression rule

Copy Code code as follows:

Pattern P=pattern.compile (String regex);

Matcher m=p.matcher (String str);

while (M.find ())

{

System.out.println (M.group ());

}

3. Web crawler Production

We make a page that can be read out of all the mailboxes in a webpage and be stored in a text file.

Copy Code code as follows:

/*
Web crawler
That is, get a string or content that matches a regular expression from a Web page

Get the mailbox address from the network
*/
Import java.io.*;
Import java.util.regex.*;
Import java.net.*;
Class MailTest
{
public static void Main (string[] args) throws Exception
{
Getmailaddr ();
}

public static void Getmailaddr () throws Exception
{
URL url=new url ("http://bbs.jb51.net/topics/390148495");
URLConnection con=url.openconnection ();

BufferedReader bufin=new BufferedReader (New InputStreamReader (Con.getinputstream ()));
BufferedWriter bufw=new BufferedWriter (New FileWriter ("E://mailaddress.txt"));
String Str=null;
String regex= "[A-za-z0-9_]{6,12}@[a-za-z0-9]+ (\\.[ a-za-z]+) + ";

Pattern P=pattern.compile (regex);
while ((Str=bufin.readline ())!=null)
{
Matcher M=p.matcher (str);
while (M.find ())
{
String Ss=m.group ();
Bufw.write (Ss,0,ss.length ());
Bufw.newline ();
Bufw.flush ();
}
}

}
}