Regular Expression Java Edition

As we all know, in the process of development, it is inevitable to encounter the need to match, find, replace, judge the occurrence of strings, and these circumstances are sometimes more complex, if the pure coding method, often waste the programmer's time and energy. Therefore, learning and using regular expressions has become the main means to solve this contradiction.
As you all know, regular expressions are a specification that can be used for pattern matching and substitution, and a regular expression is a text pattern consisting of ordinary characters (such as characters A through Z) and special characters (metacharacters), which describe one or more strings to match when looking for a text body. A regular expression, as a template, matches a character pattern to the string you are searching for.
Since jdk1.4 launched the Java.util.regex package, we have provided a good Java regular Expression application platform.

Because the regular expression is a very complex system, so I just cite some of the concepts of entry, more please refer to the relevant books and self-exploration.

Back slash
/t interval ('/u0009 ')
/N line break ('/u000a ')
/R Enter ('/u000d ')
/d number equivalent to [0-9]
/d non-numeric equivalent to [^0-9]
/s blank sign [/T/N/X0B/F/R]
/S non-blank symbol [^/T/N/X0B/F/R]
/w individual characters [a-za-z_0-9]
/w non-individual characters [^a-za-z_0-9]
/F page Break
/e Escape
/b The boundary of a word
/b A non-word boundary
/g the end of a previous match

^ Opening for the limit
^java conditions are limited to Java as the starting character
$ for Limit End
java$ conditions are limited to Java-terminated characters
. Conditions limit any single character except/n
Java.. Any two characters in addition to line breaks after a condition is restricted to Java


Add a specific restriction condition "[]"
[A-Z] condition is limited to one character in the lowercase a to Z range
[A-Z] condition is limited to one character in the uppercase A to Z range
[A-za-z] Condition limited to one character in lowercase A to Z or uppercase A to Z range
[0-9] conditions limited to one character in the lowercase 0 to 9 range
[0-9a-z] conditions are limited to one character in the lowercase 0 to 9 or a to Z range
[0-9[a-z]] condition limited to one character (intersection) in lowercase 0 to 9 or a to Z range

[] Add ^ after add again limit condition "[^]"
[^a-z] Condition limited to one character in the non-lowercase a to Z range
[^a-z] condition is limited to one character in the non-uppercase A to Z range
[^a-za-z] conditions are limited to one character in the range of non-lowercase A to Z or uppercase A to Z
[^0-9] Condition limited to one character in a non-lowercase 0 to 9 range
[^0-9a-z] conditions are limited to one character in a non-lowercase 0 to 9 or a to Z range
[^0-9[a-z]] condition limited to one character (intersection) in non-lowercase 0 to 9 or a to Z range

You can use "*" when the limit is more than 0 times for a specific character
J* more than 0 J
. * More than 0 any characters
J.*d 0 or more characters between J and D

You can use "+" when the limit is more than 1 times for a specific character
j+ more than 1 J
. + 1 + any character
J.+d 1 or more characters between J and D

You can use "?" when the limit is 0 or 1 times for a specific character
MAX J or Ja appears

Limit to consecutive occurrences of the specified number of characters "{a}"
J{2} JJ
J{3} JJJ
Text more than a, and "{a,}"
J{3,} jjj,jjjj,jjjjj,??? (3 times above J co-exist)
More than one word, B below "{a,b}"
j{3,5} JJJ or JJJJ or JJJJJ
Take a "|" of both.
j| A J or a
java| Hello java or hello

A combination type is specified in "()"
For example, I query <a href=/"index.html/" >index</a> <a href></a> between the data, can write <a.*href=/". * *" > (. +?) </a>

When using the Pattern.compile function, you can add parameters that control the matching behavior of the regular expression:
Pattern Pattern.compile (String regex, int flag)

The value range of flag is as follows:
Pattern.canon_eq The match is determined only if the "normal decomposition (canonical decomposition)" of the two characters is identical. For example, after using this flag, the expression "a/u030a" will match "?". By default, "canonical equality (canonical equivalence)" is not considered.
Pattern.case_insensitive (? i) by default, case-insensitive matching applies only to the US-ASCII character set. This flag allows the expression to ignore casing for matching. To match a Unicode character with an unknown size, just combine the unicode_case with this flag.
Pattern.comments (? x) in this mode, the match is ignored (in regular expression) empty characters (translator Note: Not refers to the expression "//s", but refers to the expression in the Space, tab, enter and so on). Comments start with # until the end of the line. You can enable UNIX line mode by using an embedded flag.
Pattern.dotall (? s) in this mode, the expression '. ' You can match any character, including the Terminator that represents a line. By default, the expression '. ' Does not match the terminator of the row.
Pattern.multiline
(? m) in this mode, ' ^ ' and ' $ ' match the start and end of a line, respectively. Also, ' ^ ' still matches the beginning of the string, ' $ ' also matches the end of the string. By default, these two expressions match only the beginning and end of a string.
Pattern.unicode_case
(? u) in this mode, if you also enable the Case_insensitive flag, it will match the uppercase and lowercase characters of the Unicode character. By default, case-insensitive matches apply only to the US-ASCII character set.
Pattern.unix_lines (? d) in this mode, only '/n ' is considered a line abort and is matched with '. ', ' ^ ', and ' $ '.


Throw away the empty concept, and write down a few simple Java regular use cases:

For example, when a string contains validation

Find a string that starts with Java and ends at any end
Pattern pattern = pattern.compile ("^java.*");
Matcher Matcher = Pattern.matcher ("Java is not human");
Boolean b= matcher.matches ();
Returns True when the condition is satisfied, otherwise false
System.out.println (b);


When splitting strings in multiple conditions
Pattern pattern = Pattern.compile ("[, |] +");
string[] STRs = Pattern.split ("Java Hello World java,hello,,world| Sun ");
for (int i=0;i<strs.length;i++) {
System.out.println (Strs[i]);
}

Text substitution (the first occurrence of a character)
Pattern pattern = pattern.compile ("Regular expression");
Matcher Matcher = Pattern.matcher ("Regular expression Hello world, regular expression Hello World");
Replace the first data that matches the regular one
System.out.println (Matcher.replacefirst ("Java"));

Text Replace (All)
Pattern pattern = pattern.compile ("Regular expression");
Matcher Matcher = Pattern.matcher ("Regular expression Hello world, regular expression Hello World");
Replace the first data that matches the regular one
System.out.println (Matcher.replaceall ("Java"));


Text substitution (substitution characters)
Pattern pattern = pattern.compile ("Regular expression");
Matcher Matcher = Pattern.matcher ("Regular expression Hello world, regular expression Hello World");
StringBuffer sbr = new StringBuffer ();
while (Matcher.find ()) {
Matcher.appendreplacement (SBR, "Java");
}
Matcher.appendtail (SBR);
System.out.println (Sbr.tostring ());

Verify that you are an e-mail address

String str= "[email protected]";
Pattern pattern = Pattern.compile ("[//w//.//-][email protected] ([//w//-]+//.) +[//w//-]+ ", pattern.case_insensitive);
Matcher Matcher = Pattern.matcher (str);
System.out.println (Matcher.matches ());

Remove HTML tags
Pattern pattern = pattern.compile ("<.+?>", Pattern.dotall);
Matcher Matcher = Pattern.matcher ("<a href=/" index.html/"> Home </a>");
String string = Matcher.replaceall ("");
System.out.println (string);

Finding the corresponding conditional string in HTML
Pattern pattern = pattern.compile ("href=/" (. +?) /"");
Matcher Matcher = Pattern.matcher ("<a href=/" index.html/"> Home </a>");
if (Matcher.find ())
System.out.println (Matcher.group (1));
}

Intercept/HTTP Address
Intercepting URLs
Pattern pattern = Pattern.compile ("(http://|https://) {1}[//w//.//-/:]+");
Matcher Matcher = Pattern.matcher ("dsdsdsStringBuffer buffer = new StringBuffer ();
while (Matcher.find ()) {
Buffer.append (Matcher.group ());
Buffer.append ("/r/n");
System.out.println (Buffer.tostring ());
}

Replace the text in the specified {}

String str = "The current History of Java is made up of {0} years-{1} years";
String[][] object={new string[]{"//{0//}", "1995"},new string[]{"//{1//}", "2007"};
SYSTEM.OUT.PRINTLN (replace (str,object));

public static string replace (final String sourcestring,object[] Object) {
String temp=sourcestring;
for (int i=0;i<object.length;i++) {
String[] result= (string[]) object[i];
Pattern pattern = pattern.compile (result[0]);
Matcher Matcher = pattern.matcher (temp);
Temp=matcher.replaceall (result[1]);
}
return temp;
}


Querying the files in the specified directory with regular conditions

For cache file List
Private ArrayList files = new ArrayList ();
Used to host file paths
Private String _path;
Used to host a regular formula that is not merged
Private String _regexp;

Class Myfilefilter implements FileFilter {

/**
* Match file name
*/
Public boolean accept (file file) {
try {
Pattern pattern = pattern.compile (_REGEXP);
Matcher match = Pattern.matcher (File.getname ());
return match.matches ();
} catch (Exception e) {
return true;
}
}
}

/**
* Parse input stream
* @param inputs
*/
Filesanalyze (String path,string regexp) {
GetFileName (PATH,REGEXP);
}

/**
* Analyze file names and add files
* @param input
*/
private void GetFileName (String path,string regexp) {
Directory
_path=path;
_regexp=regexp;
File directory = new file (_path);
file[] Filesfile = directory.listfiles (New Myfilefilter ());
if (Filesfile = = null) return;
for (int j = 0; J < Filesfile.length; J + +) {
Files.add (Filesfile[j]);
}
Return
}

/**
* Display output information
* @param out
*/
public void print (PrintStream out) {
Iterator elements = Files.iterator ();
while (Elements.hasnext ()) {
File file= (file) Elements.next ();
Out.println (File.getpath ());
}
}

public static void Output (String path,string regexp) {

Filesanalyze fileGroup1 = new Filesanalyze (PATH,REGEXP);
Filegroup1.print (System.out);
}

public static void Main (string[] args) {
Output ("c://", "[a-z|.] *");
}

Java has a lot of regular functions, in fact, as long as the character processing, there is no regular do not do things exist. (Of course, the regular explanation is more time-consuming. | | | ...... ）

Regular Expression Java Edition