Make BasicErrorController easier to subclass

Extract a new AbstractErrorController base class for users to extend
if they don't like the default BasicErrorController.

Fixes gh-3998

spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/web/AbstractErrorController.java

+/*
+ * Copyright 2012-2014 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.autoconfigure.web;
+
+import java.util.Map;
+
+import javax.servlet.http.HttpServletRequest;
+
+import org.springframework.http.HttpStatus;
+import org.springframework.stereotype.Controller;
+import org.springframework.util.Assert;
+import org.springframework.web.context.request.RequestAttributes;
+import org.springframework.web.context.request.ServletRequestAttributes;
+
+/**
+ * Abstract base class for error {@link Controller} implementations.
+ *
+ * @author Dave Syer
+ * @author Phillip Webb
+ * @see ErrorAttributes
+ * @since 1.3.0
+ */
+public abstract class AbstractErrorController implements ErrorController {
+
+	private final ErrorAttributes errorAttributes;
+
+	public AbstractErrorController(ErrorAttributes errorAttributes) {
+		Assert.notNull(errorAttributes, "ErrorAttributes must not be null");
+		this.errorAttributes = errorAttributes;
+	}
+
+	protected boolean getTraceParameter(HttpServletRequest request) {
+		String parameter = request.getParameter("trace");
+		if (parameter == null) {
+			return false;
+		}
+		return !"false".equals(parameter.toLowerCase());
+	}
+
+	protected Map<String, Object> getErrorAttributes(HttpServletRequest request) {
+		return getErrorAttributes(request, getTraceParameter(request));
+	}
+
+	protected Map<String, Object> getErrorAttributes(HttpServletRequest request,
+			boolean includeStackTrace) {
+		RequestAttributes requestAttributes = new ServletRequestAttributes(request);
+		return this.errorAttributes.getErrorAttributes(requestAttributes,
+				includeStackTrace);
+	}
+
+	protected HttpStatus getStatus(HttpServletRequest request) {
+		Integer statusCode = (Integer) request
+				.getAttribute("javax.servlet.error.status_code");
+		if (statusCode == null) {
+			return HttpStatus.INTERNAL_SERVER_ERROR;
+		}
+		try {
+			return HttpStatus.valueOf(statusCode);
+		}
+		catch (Exception ex) {
+			return HttpStatus.INTERNAL_SERVER_ERROR;
+		}
+	}
+
+}

spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/web/BasicErrorController.java

@@ -25,11 +25,8 @@ import org.springframework.boot.context.embedded.AbstractEmbeddedServletContaine
 import org.springframework.http.HttpStatus;
 import org.springframework.http.ResponseEntity;
 import org.springframework.stereotype.Controller;
-import org.springframework.util.Assert;
 import org.springframework.web.bind.annotation.RequestMapping;
 import org.springframework.web.bind.annotation.ResponseBody;
-import org.springframework.web.context.request.RequestAttributes;
-import org.springframework.web.context.request.ServletRequestAttributes;
 import org.springframework.web.servlet.ModelAndView;
 
 /**
@@ -44,16 +41,13 @@ import org.springframework.web.servlet.ModelAndView;
  */
 @Controller
 @RequestMapping("${error.path:/error}")
-public class BasicErrorController implements ErrorController {
+public class BasicErrorController extends AbstractErrorController {
 
 	@Value("${error.path:/error}")
 	private String errorPath;
 
-	private final ErrorAttributes errorAttributes;
-
 	public BasicErrorController(ErrorAttributes errorAttributes) {
-		Assert.notNull(errorAttributes, "ErrorAttributes must not be null");
-		this.errorAttributes = errorAttributes;
+		super(errorAttributes);
 	}
 
 	@Override
@@ -74,37 +68,4 @@ public class BasicErrorController implements ErrorController {
 		return new ResponseEntity<Map<String, Object>>(body, status);
 	}
 
-	private boolean getTraceParameter(HttpServletRequest request) {
-		String parameter = request.getParameter("trace");
-		if (parameter == null) {
-			return false;
-		}
-		return !"false".equals(parameter.toLowerCase());
-	}
-
-	protected Map<String, Object> getErrorAttributes(HttpServletRequest request) {
-		return getErrorAttributes(request, getTraceParameter(request));
-	}
-
-	protected Map<String, Object> getErrorAttributes(HttpServletRequest request,
-			boolean includeStackTrace) {
-		RequestAttributes requestAttributes = new ServletRequestAttributes(request);
-		return this.errorAttributes.getErrorAttributes(requestAttributes,
-				includeStackTrace);
-	}
-
-	protected HttpStatus getStatus(HttpServletRequest request) {
-		Integer statusCode = (Integer) request
-				.getAttribute("javax.servlet.error.status_code");
-		if (statusCode == null) {
-			return HttpStatus.INTERNAL_SERVER_ERROR;
-		}
-		try {
-			return HttpStatus.valueOf(statusCode);
-		}
-		catch (Exception ex) {
-			return HttpStatus.INTERNAL_SERVER_ERROR;
-		}
-	}
-
 }