fixed JSP EvalTag to render null result as empty String instead of "null" String (SPR-7459)

org.springframework.web.servlet/src/main/java/org/springframework/web/servlet/tags/EvalTag.java

@@ -32,6 +32,7 @@ import org.springframework.expression.TypedValue;
 import org.springframework.expression.spel.standard.SpelExpressionParser;
 import org.springframework.expression.spel.support.StandardEvaluationContext;
 import org.springframework.expression.spel.support.StandardTypeConverter;
+import org.springframework.util.ObjectUtils;
 import org.springframework.web.util.ExpressionEvaluationUtils;
 import org.springframework.web.util.HtmlUtils;
 import org.springframework.web.util.JavaScriptUtils;
@@ -103,21 +104,22 @@ public class EvalTag extends HtmlEscapingAwareTag {
 		if (this.evaluationContext == null) {
 			this.evaluationContext = createEvaluationContext(pageContext);
 		}
-		if (this.var == null) {
+		if (this.var != null) {
+			Object result = this.expression.getValue(this.evaluationContext);
+			pageContext.setAttribute(this.var, result, this.scope);
+		}
+		else {
 			try {
 				String result = this.expression.getValue(this.evaluationContext, String.class);
-				result = isHtmlEscape() ? HtmlUtils.htmlEscape(result) : result;
-				result = this.javaScriptEscape ? JavaScriptUtils.javaScriptEscape(result) : result;
+				result = ObjectUtils.getDisplayString(result);
+				result = (isHtmlEscape() ? HtmlUtils.htmlEscape(result) : result);
+				result = (this.javaScriptEscape ? JavaScriptUtils.javaScriptEscape(result) : result);
 				pageContext.getOut().print(result);
 			}
 			catch (IOException ex) {
 				throw new JspException(ex);
 			}
 		}
-		else {
-			Object result = this.expression.getValue(this.evaluationContext);
-			pageContext.setAttribute(this.var, result, this.scope);
-		}
 		return EVAL_PAGE;
 	}
 

org.springframework.web.servlet/src/test/java/org/springframework/web/servlet/tags/EvalTagTests.java

@@ -52,9 +52,18 @@ public class EvalTagTests extends AbstractTagTests {
 		assertEquals(Tag.EVAL_BODY_INCLUDE, action);
 		action = tag.doEndTag();
 		assertEquals(Tag.EVAL_PAGE, action);
-		assertEquals("foo", ((MockHttpServletResponse)context.getResponse()).getContentAsString());
+		assertEquals("foo", ((MockHttpServletResponse) context.getResponse()).getContentAsString());
 	}
-	
+
+	public void testPrintNullAsEmptyString() throws Exception {
+		tag.setExpression("bean.null");
+		int action = tag.doStartTag();
+		assertEquals(Tag.EVAL_BODY_INCLUDE, action);
+		action = tag.doEndTag();
+		assertEquals(Tag.EVAL_PAGE, action);
+		assertEquals("", ((MockHttpServletResponse) context.getResponse()).getContentAsString());
+	}
+
 	public void testPrintFormattedScopedAttributeResult() throws Exception {
 		tag.setExpression("bean.formattable");
 		int action = tag.doStartTag();
@@ -63,7 +72,7 @@ public class EvalTagTests extends AbstractTagTests {
 		assertEquals(Tag.EVAL_PAGE, action);
 		assertEquals("25%", ((MockHttpServletResponse) context.getResponse()).getContentAsString());
 	}
-	
+
 	public void testPrintHtmlEscapedAttributeResult() throws Exception {
 		tag.setExpression("bean.html()");
 		tag.setHtmlEscape("true");
@@ -71,7 +80,7 @@ public class EvalTagTests extends AbstractTagTests {
 		assertEquals(Tag.EVAL_BODY_INCLUDE, action);
 		action = tag.doEndTag();
 		assertEquals(Tag.EVAL_PAGE, action);
-		assertEquals("<p>", ((MockHttpServletResponse)context.getResponse()).getContentAsString());
+		assertEquals("<p>", ((MockHttpServletResponse) context.getResponse()).getContentAsString());
 	}
 
 	public void testPrintJavaScriptEscapedAttributeResult() throws Exception {
@@ -133,10 +142,15 @@ public class EvalTagTests extends AbstractTagTests {
 		public String html() {
 			return "<p>";
 		}
+
 		public String getBean() {
 			return "not the bean object";
 		}
 		
+		public Object getNull() {
+			return null;
+		}
+
 		public String js() {
 			return "function foo() { alert(\"hi\") }";
 		}