Set value of javax.servlet.error.exception_type to a Class not a String

Previously, ErrorPageFilter set the value of
javax.servlet.error.exception_type to be the name of the exception,
(a java.lang.String). This commit changes it to be a java.lang.Class
as required by the Servlet spec.

Closes gh-7925

spring-boot/src/main/java/org/springframework/boot/web/support/ErrorPageFilter.java

@@ -179,7 +179,7 @@ public class ErrorPageFilter implements Filter, ErrorPageRegistry {
 		}
 		setErrorAttributes(request, 500, ex.getMessage());
 		request.setAttribute(ERROR_EXCEPTION, ex);
-		request.setAttribute(ERROR_EXCEPTION_TYPE, ex.getClass().getName());
+		request.setAttribute(ERROR_EXCEPTION_TYPE, ex.getClass());
 		response.reset();
 		response.sendError(500, ex.getMessage());
 		request.getRequestDispatcher(path).forward(request, response);

spring-boot/src/test/java/org/springframework/boot/web/support/ErrorPageFilterTests.java

@@ -262,7 +262,7 @@ public class ErrorPageFilterTests {
 		assertThat(this.request.getAttribute(RequestDispatcher.ERROR_MESSAGE))
 				.isEqualTo("BAD");
 		assertThat(this.request.getAttribute(RequestDispatcher.ERROR_EXCEPTION_TYPE))
-				.isEqualTo(RuntimeException.class.getName());
+				.isEqualTo(RuntimeException.class);
 		assertThat(this.request.getAttribute(RequestDispatcher.ERROR_REQUEST_URI))
 				.isEqualTo("/test/path");
 		assertThat(this.response.isCommitted()).isTrue();
@@ -319,7 +319,7 @@ public class ErrorPageFilterTests {
 		assertThat(this.request.getAttribute(RequestDispatcher.ERROR_MESSAGE))
 				.isEqualTo("BAD");
 		assertThat(this.request.getAttribute(RequestDispatcher.ERROR_EXCEPTION_TYPE))
-				.isEqualTo(IllegalStateException.class.getName());
+				.isEqualTo(IllegalStateException.class);
 		assertThat(this.request.getAttribute(RequestDispatcher.ERROR_REQUEST_URI))
 				.isEqualTo("/test/path");
 		assertThat(this.response.isCommitted()).isTrue();
@@ -493,7 +493,7 @@ public class ErrorPageFilterTests {
 		assertThat(this.request.getAttribute(RequestDispatcher.ERROR_MESSAGE))
 				.isEqualTo("BAD");
 		assertThat(this.request.getAttribute(RequestDispatcher.ERROR_EXCEPTION_TYPE))
-				.isEqualTo(RuntimeException.class.getName());
+				.isEqualTo(RuntimeException.class);
 		assertThat(this.request.getAttribute(RequestDispatcher.ERROR_REQUEST_URI))
 				.isEqualTo("/test/path");
 		assertThat(this.response.isCommitted()).isTrue();