Add generic error handling to BasicErrorController

Since Spring supports gobal error handling through
@ControllerAdvice, it is quite easy to set up more meta-data
about an exception for the BasicErrorController. You need
to be careful not to swallow Security exceptions, and probably
others (optionally) so this feature needs a bit more work.

See gh-538

spring-boot-actuator/src/test/java/org/springframework/boot/actuate/web/BasicErrorControllerIntegrationTests.java

@@ -18,6 +18,8 @@ package org.springframework.boot.actuate.web;
 
 import java.util.Map;
 
+import javax.servlet.DispatcherType;
+import javax.servlet.ServletContext;
 import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpServletResponse;
 
@@ -35,11 +37,16 @@ import org.springframework.boot.test.SpringApplicationConfiguration;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.http.MediaType;
+import org.springframework.mock.web.MockHttpServletRequest;
 import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
 import org.springframework.test.context.web.WebAppConfiguration;
 import org.springframework.test.web.servlet.MockMvc;
 import org.springframework.test.web.servlet.MvcResult;
+import org.springframework.test.web.servlet.RequestBuilder;
 import org.springframework.test.web.servlet.setup.MockMvcBuilders;
+import org.springframework.validation.BindException;
+import org.springframework.web.bind.annotation.RequestMapping;
+import org.springframework.web.bind.annotation.RestController;
 import org.springframework.web.context.WebApplicationContext;
 import org.springframework.web.servlet.View;
 import org.springframework.web.servlet.view.AbstractView;
@@ -67,7 +74,7 @@ public class BasicErrorControllerIntegrationTests {
 	}
 
 	@Test
-	public void testErrorForMachineClient() throws Exception {
+	public void testDirectAccessForMachineClient() throws Exception {
 		MvcResult response = this.mockMvc.perform(get("/error"))
 				.andExpect(status().is5xxServerError()).andReturn();
 		String content = response.getResponse().getContentAsString();
@@ -75,7 +82,32 @@ public class BasicErrorControllerIntegrationTests {
 	}
 
 	@Test
-	public void testErrorForBrowserClient() throws Exception {
+	public void testErrorForMachineClient() throws Exception {
+		MvcResult result = this.mockMvc.perform(get("/"))
+				.andExpect(status().is5xxServerError()).andReturn();
+		MvcResult response = this.mockMvc.perform(new ErrorDispatcher(result, "/error"))
+				.andReturn();
+		String content = response.getResponse().getContentAsString();
+		assertTrue("Wrong content: " + content, content.contains("Expected!"));
+	}
+
+	@Test
+	public void testBindingExceptionForMachineClient() throws Exception {
+		// In a real container the response is carried over into the error dispatcher, but
+		// in the mock a new one is created so we have to assert the status at this
+		// intermediate point
+		MvcResult result = this.mockMvc.perform(get("/bind"))
+				.andExpect(status().is4xxClientError()).andReturn();
+		MvcResult response = this.mockMvc.perform(new ErrorDispatcher(result, "/error"))
+				.andReturn();
+		// And the rendered status code is always wrong (but would be 400 in a real
+		// system)
+		String content = response.getResponse().getContentAsString();
+		assertTrue("Wrong content: " + content, content.contains("Error count: 1"));
+	}
+
+	@Test
+	public void testDirectAccessForBrowserClient() throws Exception {
 		MvcResult response = this.mockMvc
 				.perform(get("/error").accept(MediaType.TEXT_HTML))
 				.andExpect(status().isOk()).andReturn();
@@ -106,6 +138,46 @@ public class BasicErrorControllerIntegrationTests {
 			};
 		}
 
+		@RestController
+		protected static class Errors {
+
+			public String getFoo() {
+				return "foo";
+			}
+
+			@RequestMapping("/")
+			public String home() {
+				throw new IllegalStateException("Expected!");
+			}
+
+			@RequestMapping("/bind")
+			public String bind() throws Exception {
+				BindException error = new BindException(this, "test");
+				error.rejectValue("foo", "bar.error");
+				throw error;
+			}
+
+		}
+
+	}
+
+	private class ErrorDispatcher implements RequestBuilder {
+
+		private MvcResult result;
+		private String path;
+
+		public ErrorDispatcher(MvcResult result, String path) {
+			this.result = result;
+			this.path = path;
+		}
+
+		@Override
+		public MockHttpServletRequest buildRequest(ServletContext servletContext) {
+			MockHttpServletRequest request = this.result.getRequest();
+			request.setDispatcherType(DispatcherType.ERROR);
+			request.setRequestURI(this.path);
+			return request;
+		}
 	}
 
 }