Ensure status in ErrorPageFilter defaults to 200

Fixes gh-1369. Note that this is caused by the ErrorPageFilter, so
only a problem when deployed as a WAR.

spring-boot-actuator/src/main/java/org/springframework/boot/actuate/autoconfigure/MetricFilterAutoConfiguration.java

@@ -93,10 +93,17 @@ public class MetricFilterAutoConfiguration {
 				int status = getStatus(response);
 				Object bestMatchingPattern = request
 						.getAttribute(HandlerMapping.BEST_MATCHING_PATTERN_ATTRIBUTE);
+				HttpStatus httpStatus = HttpStatus.OK;
+				try {
+					httpStatus = HttpStatus.valueOf(status);
+				}
+				catch (Exception e) {
+					// not convertible
+				}
 				if (bestMatchingPattern != null) {
 					suffix = bestMatchingPattern.toString().replaceAll("[{}]", "-");
 				}
-				else if (HttpStatus.valueOf(status).is4xxClientError()) {
+				else if (httpStatus.is4xxClientError()) {
 					suffix = UNKNOWN_PATH_SUFFIX;
 				}
 				String gaugeKey = getKey("response" + suffix);

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

@@ -239,6 +239,7 @@ class ErrorPageFilter extends AbstractConfigurableEmbeddedServletContainer imple
 
 		public ErrorWrapperResponse(HttpServletResponse response) {
 			super(response);
+			this.status = response.getStatus();
 		}
 
 		@Override

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

@@ -205,6 +205,21 @@ public class ErrorPageFilterTests {
 		assertTrue(this.response.isCommitted());
 	}
 
+	@Test
+	public void statusCode() throws Exception {
+		this.chain = new MockFilterChain() {
+			@Override
+			public void doFilter(ServletRequest request, ServletResponse response)
+					throws IOException, ServletException {
+				assertThat(((HttpServletResponse) response).getStatus(), equalTo(200));
+				super.doFilter(request, response);
+			}
+		};
+		this.filter.doFilter(this.request, this.response, this.chain);
+		assertThat(((HttpServletResponseWrapper) this.chain.getResponse()).getStatus(),
+				equalTo(200));
+	}
+
 	@Test
 	public void subClassExceptionError() throws Exception {
 		this.filter.addErrorPages(new ErrorPage(RuntimeException.class, "/500"));