java多次替换(replace不行)

import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class test {

    public static void main(String args[])
    {
        String a="[<<>><<>>]";

        String regEx_script="<";
        String regEx_style= ">";  

         //过滤script标签
        Pattern p_script=Pattern.compile(regEx_script,Pattern.CASE_INSENSITIVE);
        Matcher m_script = p_script.matcher(a);
        a = m_script.replaceAll("&lt;");

        Pattern p_style = Pattern.compile(regEx_style,Pattern.CASE_INSENSITIVE);
        Matcher m_style = p_style.matcher(a);
        a= m_style.replaceAll("&gt;");
        System.out.println(a);
    }
}