使用正则表达式获取两个字符串之间的子字符串

Question

I have xml files containing code like

<bean id="ParentDataSource" class="com.mchange.v2.c3p0.ComboPooledDataSource">
    <property name="driverClass" value="${JDBC.MYSQL.DRIVER}" />
    <property name="password" value="${JDBC.MYSQL.PASSWORD}" />
    <property name="user" value="${JDBC.MYSQL.USERNAME}" />
</bean>

I want to get all tokens between value={ and } using java code. for above text needs below output :

JDBC.MYSQL.DRIVER 
JDBC.MYSQL.PASSWORD
JDBC.MYSQL.USERNAME

I tried with following code but could not able to add $ symbol in regex.

BufferedReader reader = new BufferedReader(new FileReader(file));
Pattern pattern = Pattern.compile("value=\"$(.*?)}");
String line;
while((line=reader.readLine())!=null) {
    Matcher matcher = pattern.matcher(line);
    System.out.println(matcher.group(1));
}

Please suggest some solution.

Answer 1

This does look an awful lot of spring, which has build in methods to replace ${var_name} with a value taken from a .properties file:

<bean class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
    <property name="location" value="database.properties"/>
</bean>

This nice snippet while replace the ${var_name} in your XML files with the actual value when loading the application context.

Answer 2

Try this:

String input = "abcabc pattern1foopattern2 abcdefg pattern1barpattern2 morestuff";
    List<String> strings = Arrays.asList( input.replaceAll("^.*?pattern1", "").split("pattern2.*?(pattern1|$)"));
    System.out.println( strings);

Answer 3

i would recommend using an XML parser.

Try this

import java.io.File;

import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;

import org.w3c.dom.Document;
import org.w3c.dom.NodeList;
import org.w3c.dom.NamedNodeMap;

public class Demo {

public static void main(String[] args) throws Exception {

  DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
  DocumentBuilder db = dbf.newDocumentBuilder();
  Document document = db.parse(new File("sample.xml"));
  NodeList propertyList = document.getElementsByTagName("property");

  if(propertyList !=null && propertyList.getLength() > 0) {
    for(int i =0; i< propertyList.getLength(); i++) {
      NamedNodeMap node = propertyList.item(i).getAttributes();
      System.out.println(node.getNamedItem("value").getNodeValue());
    }
  }
}
}

Answer 4

There are several problems with your regex. First of all, you have missed the { character. Secondly, you need to escape both the { , } and $ characters since they are special characters. So, this will work:

Pattern pattern = Pattern.compile("value=\"\\$\\{(.*?)\\}");

Also, you will need to call matcher.find() :

if (matcher.find()) {    
    System.out.println(matcher.group(1));
}

Answer 5

A few issues: you need to escape some of the special characters in the regexp, and most importantly, you need to call a method on the matcher, such as find() , to get it to do the matching. Try this:

    Pattern pattern = Pattern.compile("\\$\\{(.*)\\}");
    Matcher matcher = pattern.matcher(s);
    if (matcher.find()) {
        System.out.println(matcher.group(1));
    } else {
        System.out.println("not found");
    }

Note that the regexp requires $ and { and } to be escaped with a backslash. And since you want an actual backslash in the string, you have to provide a double backslash.

This seems to work, as long as there's only one occurrence of ${...} on a line. If there are two, the match group will match from the start of the first to the end of the second! For example, if the input is

    abc${FOO}def${BAR}ghi

the group will match FOO}def${BAR which is probably not what you want. If you need to handle this, you can use something like

    Pattern pattern = Pattern.compile("\\$\\{([^}]*)\\}");

This avoids the spanning problem. However, this matches only the first occurrence. Do deal with multiple matches, you have to write an inner loop that starts the next match at the end of the previous one.