请告诉我如何在字符串中获取Xml声明？
例如：
<?xml version="1.0" encoding="UTF-8"?><!DOCTYPE KEA-publ PUBLIC "-//KLI//DTD KEA-BASIC//EN" "keabasic.dtd" [
<!ENTITY SLSD_158790_gif SYSTEM "IEL-Environment-109-Taiwan_aw01.gif" NDATA GIF>
<!ENTITY SLSD_158791_gif SYSTEM "IEL-Environment-109-Taiwan_aw02.gif" NDATA GIF>
<!ENTITY SLSD_158792_gif SYSTEM "IEL-Environment-109-Taiwan_aw03.gif" NDATA GIF>
<!ENTITY SLSD_158493_gif SYSTEM "IEL-Environment-109-Taiwan_aw04.gif" NDATA GIF>
<!ENTITY SLSD_158794_gif SYSTEM "IEL-Environment-109-Taiwan_aw05.gif" NDATA GIF>
<!ENTITY SLSD_158795_gif SYSTEM "IEL-Environment-109-Taiwan_aw06.gif" NDATA GIF>
<!ENTITY SLSD_158796_gif SYSTEM "IEL-Environment-109-Taiwan_aw07.gif" NDATA GIF>
<!ENTITY SLSD_158797_gif SYSTEM "IEL-Environment-109-Taiwan_aw08.gif" NDATA GIF>
<!ENTITY SLSD_158g98_gif SYSTEM "IEL-Environment-109-Taiwan_aw09.gif" NDATA GIF>
<!ENTITY SLSD_158499_gif SYSTEM "IEL-Environment-109-Taiwan_aw10.gif" NDATA GIF>
]>
如何获取xml文件的上述声明部分