String html = "<html><script>if(a<0){...}</script><body><p>abc<br>def</p>text1<br>text2<BR>text3</body></html>";
Pattern pattern1 = Pattern.compile("<(br|BR)>", Pattern.DOTALL);
Matcher matcher1 = pattern1.matcher(html);
String s = matcher1.replaceAll("\r\n");
System.out.println(s);