Missing path variable is now a 500 error

Before this change a missing path variable value resulted in a 400
error where in fact the error is due to a mismatch between the
declared @PathVariable and the URI template, i.e. a 500 error.

This change introduced a MissingPathVariableException as a sub-class
of ServletRequestBindingException (the exception previously thrown)
and results in a response status code of 500 by default.

Issue: SPR-13121

spring-web/src/main/java/org/springframework/web/bind/MissingPathVariableException.java

@@ -0,0 +1,71 @@
+/*
+ * Copyright 2002-2015 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.web.bind;
+
+import org.springframework.core.MethodParameter;
+
+/**
+ * {@link ServletRequestBindingException} subclass that indicates that a path
+ * variable expected in the method parameters of an {@code @RequestMapping}
+ * method is not present among the URI variables extracted from the URL.
+ * Typically that means the URI template does not match the path variable name
+ * declared on the method parameter.
+ *
+ * @author Rossen Stoyanchev
+ * @since 4.2
+ */
+@SuppressWarnings("serial")
+public class MissingPathVariableException extends ServletRequestBindingException {
+
+	private final String variableName;
+
+	private final MethodParameter parameter;
+
+
+	/**
+	 * Constructor for MissingPathVariableException.
+	 * @param variableName the name of the missing path variable
+	 * @param parameter the method parameter
+	 */
+	public MissingPathVariableException(String variableName, MethodParameter parameter) {
+		super("");
+		this.variableName = variableName;
+		this.parameter = parameter;
+	}
+
+
+	@Override
+	public String getMessage() {
+		return "Missing URI template variable '" + this.variableName +
+				"' for method parameter of type " + parameter.getParameterType().getSimpleName();
+	}
+
+	/**
+	 * Return the expected name of the path variable.
+	 */
+	public final String getVariableName() {
+		return this.variableName;
+	}
+
+	/**
+	 * Return the method parameter bound to the path variable.
+	 */
+	public final MethodParameter getParameter() {
+		return this.parameter;
+	}
+
+}