test: add bigInterger for expression vul

Author: ReaJason

vul/vul-webapp-expression/src/main/java/BigIntegerClassLaoderServlet.java

@@ -0,0 +1,48 @@
+import javax.servlet.*;
+import javax.servlet.annotation.WebServlet;
+import java.io.IOException;
+
+/**
+ * @author Wans
+ * @since 2025/08/25
+ */
+@WebServlet("/biginteger")
+public class BigIntegerClassLaoderServlet extends ClassLoader implements Servlet {
+
+    @Override
+    public void init(ServletConfig config) throws ServletException {
+
+    }
+
+    @Override
+    public ServletConfig getServletConfig() {
+        return null;
+    }
+
+    @Override
+    public void service(ServletRequest req, ServletResponse res) throws ServletException, IOException {
+        String data = req.getParameter("data");
+        try {
+            byte[] bytes = decodeBigInteger(data);
+            Object obj = defineClass(null, bytes, 0, bytes.length).newInstance();
+            res.getWriter().print(obj);
+        } catch (Exception e) {
+            throw new RuntimeException(e);
+        }
+    }
+
+    static byte[] decodeBigInteger(String bigIntegerStr) throws Exception {
+        Class<?> decoderClass = Class.forName("java.math.BigInteger");
+        return (byte[]) decoderClass.getMethod("toByteArray").invoke(decoderClass.getConstructor(String.class, int.class).newInstance(bigIntegerStr, Character.MAX_RADIX));
+    }
+
+    @Override
+    public String getServletInfo() {
+        return "";
+    }
+
+    @Override
+    public void destroy() {
+
+    }
+}