Prepend context/servlet path to FormTag action

The Form tag now fills in the context and servlet path if not present
in the specified action.

Issue: SPR-8684

spring-webmvc/src/main/java/org/springframework/web/servlet/support/RequestContext.java

@@ -36,6 +36,7 @@ import org.springframework.ui.context.ThemeSource;
 import org.springframework.ui.context.support.ResourceBundleThemeSource;
 import org.springframework.util.Assert;
 import org.springframework.util.ClassUtils;
+import org.springframework.util.StringUtils;
 import org.springframework.validation.BindException;
 import org.springframework.validation.BindingResult;
 import org.springframework.validation.Errors;
@@ -422,14 +423,14 @@ public class RequestContext {
 	 * context path and the servlet path of the original request. This is useful
 	 * for building links to other resources within the application where a
 	 * servlet mapping of the style {@code "/main/*"} is used.
-	 * <p>Delegates to the UrlPathHelper for decoding the context path.
-	 * @see javax.servlet.http.HttpServletRequest#getContextPath
-	 * @see javax.servlet.http.HttpServletRequest#getServletPath()
-	 * @see #getUrlPathHelper
+	 * Delegates to the UrlPathHelper to determine the context and servlet path.
 	 */
 	public String getPathToServlet() {
-		return this.urlPathHelper.getOriginatingContextPath(this.request)
-				+ this.urlPathHelper.getOriginatingServletPath(this.request);
+		String path = this.urlPathHelper.getOriginatingContextPath(this.request);
+		if (StringUtils.hasText(this.urlPathHelper.getPathWithinServletMapping(this.request))) {
+			path += this.urlPathHelper.getOriginatingServletPath(this.request);
+		}
+		return path;
 	}
 
 	/**

spring-webmvc/src/main/java/org/springframework/web/servlet/tags/form/FormTag.java

@@ -32,6 +32,7 @@ import org.springframework.util.ObjectUtils;
 import org.springframework.util.StringUtils;
 import org.springframework.web.servlet.support.RequestDataValueProcessor;
 import org.springframework.web.util.HtmlUtils;
+import org.springframework.web.util.UrlPathHelper;
 
 /**
  * Databinding-aware JSP tag for rendering an HTML '{@code form}' whose
@@ -411,6 +412,10 @@ public class FormTag extends AbstractHtmlElementTag {
 	protected String resolveAction() throws JspException {
 		String action = getAction();
 		if (StringUtils.hasText(action)) {
+			String pathToServlet = getRequestContext().getPathToServlet();
+			if (action.startsWith("/") && !action.startsWith(getRequestContext().getContextPath())) {
+				action = pathToServlet + action;
+			}
 			action = getDisplayString(evaluate(ACTION_ATTRIBUTE, action));
 			return processAction(action);
 		}

spring-webmvc/src/test/java/org/springframework/web/servlet/tags/form/FormTagTests.java

@@ -166,6 +166,50 @@ public class FormTagTests extends AbstractHtmlElementTagTests {
 		assertAttributeNotPresent(output, "name");
 	}
 
+	public void testPrependServletPath() throws Exception {
+
+		this.request.setContextPath("/myApp");
+		this.request.setServletPath("/main");
+		this.request.setPathInfo("/index.html");
+
+		String commandName = "myCommand";
+		String action = "/form.html";
+		String enctype = "my/enctype";
+		String method = "POST";
+		String onsubmit = "onsubmit";
+		String onreset = "onreset";
+
+		this.tag.setCommandName(commandName);
+		this.tag.setAction(action);
+		this.tag.setMethod(method);
+		this.tag.setEnctype(enctype);
+		this.tag.setOnsubmit(onsubmit);
+		this.tag.setOnreset(onreset);
+
+		int result = this.tag.doStartTag();
+		assertEquals(Tag.EVAL_BODY_INCLUDE, result);
+		assertEquals("Form attribute not exposed", commandName,
+				getPageContext().getAttribute(FormTag.MODEL_ATTRIBUTE_VARIABLE_NAME, PageContext.REQUEST_SCOPE));
+
+		result = this.tag.doEndTag();
+		assertEquals(Tag.EVAL_PAGE, result);
+
+		this.tag.doFinally();
+		assertNull("Form attribute not cleared after tag ends",
+				getPageContext().getAttribute(FormTag.MODEL_ATTRIBUTE_VARIABLE_NAME, PageContext.REQUEST_SCOPE));
+
+		String output = getOutput();
+		assertFormTagOpened(output);
+		assertFormTagClosed(output);
+
+		assertContainsAttribute(output, "action", "/myApp/main/form.html");
+		assertContainsAttribute(output, "method", method);
+		assertContainsAttribute(output, "enctype", enctype);
+		assertContainsAttribute(output, "onsubmit", onsubmit);
+		assertContainsAttribute(output, "onreset", onreset);
+		assertAttributeNotPresent(output, "name");
+	}
+
 	public void testWithNullResolvedCommand() throws Exception {
 		try {
 			tag.setCommandName("${null}");