[SLING-577] Patch Submission: JSP tag to evaluate JCR properties using EL

• Type: New Feature
• Status: Resolved
• Priority: Major
• Resolution: Won't Fix
• Component/s: Scripting
• Assignee: Felix Meschberger
• Reporter: David Trott
• Created: 23/Jul/08 04:04
• Updated: 25/Feb/13 17:01
• Resolved: 25/Feb/13 17:01

Description

Use case
========
Say you are building components in sling and you want to break the logic into two separate components:

• One to fetch the data (possibly from a DB) and populate the pageContext.
• And one to render some HTML using data in the pageContext.

This would allow either component to be switched out without affecting the other.

In this scenario we need a way to connect the two components together; one option is to use EL
Hence we could define a property of the content node for the visual component: rating="${dbrating}"

This assumes that the DB component has already done a pageContext.setAttribute("dbrating", "some value");

We can then build a JSP page which evaluates the properties, e.g:

<h1>Current Rating: '<sling:evalProperty property="rating"/>'</h1>

Hence this JSP page would form the core of the visual component.

Patch File
========

diff -Nur jsp-taglib-base/src/main/java/org/apache/sling/scripting/jsp/taglib/EvalPropertyTEI.java jsp-taglib-update/src/main/java/org/apache/sling/scripting/jsp/taglib/EvalPropertyTEI.java
— jsp-taglib-base/src/main/java/org/apache/sling/scripting/jsp/taglib/EvalPropertyTEI.java 1969-12-31 16:00:00.000000000 -0800
+++ jsp-taglib-update/src/main/java/org/apache/sling/scripting/jsp/taglib/EvalPropertyTEI.java 2008-07-22 20:25:57.000000000 -0700
@@ -0,0 +1,74 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You 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.apache.sling.scripting.jsp.taglib;
+
+import static org.apache.sling.scripting.jsp.taglib.EvalPropertyTag.DEFAULT_VAR;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import javax.servlet.jsp.tagext.TagData;
+import javax.servlet.jsp.tagext.TagExtraInfo;
+import javax.servlet.jsp.tagext.VariableInfo;
+
+/**
+ * This class defines the scripting variables that are created by the
+ * <code>EvalPropertyTag</code>.
+ */
+public class EvalPropertyTEI extends TagExtraInfo {
+
+ /**
+ * The name of the tag attribute used to define the name of the
+ * value scripting variable (value is "var").
+ */
+ public static final String ATTR_VAR = "var";
+
+ private static final String VAR_CLASS = String.class.getName();
+
+ /**
+ * Returns an Array of <code>VariableInfo</code> objects describing
+ * scripting variables.
+ *
+ * @see javax.servlet.jsp.tagext.TagExtraInfo#getVariableInfo(TagData)
+ */
+ public VariableInfo[] getVariableInfo(TagData data)

{ + + List<VariableInfo> varInfos = new ArrayList<VariableInfo>(); + + addVar(varInfos, data, ATTR_VAR, DEFAULT_VAR, VAR_CLASS); + + return varInfos.toArray(new VariableInfo[varInfos.size()]); + + }

+
+ private void addVar(List<VariableInfo> varInfos, TagData data, String attrName, String defaultValue, String varClass) {
+ String value = getValue(data, attrName, defaultValue);
+
+ if (value != null && varClass != null)

{ + varInfos.add(new VariableInfo(value, varClass, true, VariableInfo.AT_END)); + }

+ }
+
+ private String getValue(TagData data, String name, String defaultValue) {
+ Object value = data.getAttribute(name);
+ if (value instanceof String)

{ + return (String) value; + }

+
+ return defaultValue;
+ }
+}
diff -Nur jsp-taglib-base/src/main/java/org/apache/sling/scripting/jsp/taglib/EvalPropertyTag.java jsp-taglib-update/src/main/java/org/apache/sling/scripting/jsp/taglib/EvalPropertyTag.java
— jsp-taglib-base/src/main/java/org/apache/sling/scripting/jsp/taglib/EvalPropertyTag.java 1969-12-31 16:00:00.000000000 -0800
+++ jsp-taglib-update/src/main/java/org/apache/sling/scripting/jsp/taglib/EvalPropertyTag.java 2008-07-22 20:25:57.000000000 -0700
@@ -0,0 +1,137 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You 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.apache.sling.scripting.jsp.taglib;
+
+import java.io.IOException;
+
+import javax.el.ELContext;
+import javax.el.ExpressionFactory;
+import javax.jcr.Node;
+import javax.jcr.PathNotFoundException;
+import javax.jcr.Property;
+import javax.jcr.RepositoryException;
+import javax.servlet.ServletRequest;
+import javax.servlet.jsp.JspException;
+import javax.servlet.jsp.JspFactory;
+import javax.servlet.jsp.tagext.TagSupport;
+
+import org.apache.sling.api.resource.Resource;
+import org.apache.sling.api.resource.ResourceResolver;
+import org.apache.sling.api.scripting.SlingBindings;
+import org.apache.sling.api.scripting.SlingScriptHelper;
+
+/**
+ * The <code>EvalPropertyTag</code> implements the
+ * <code><sling:evalProperty></code> custom tag.
+ */
+public class EvalPropertyTag extends TagSupport {
+
+ /**
+ * Default name for the scripting variable set to the result
+ * of the evaluation (value is null).
+ */
+ public static final String DEFAULT_VAR = null;
+
+ /**
+ * The default path if no path attribute is passed to the tag (value is ".").
+ */
+ public static final String DEFAULT_PATH = ".";
+
+ private String var = DEFAULT_VAR;
+
+ private String path = DEFAULT_PATH;
+
+ private String property;
+
+ /**
+ * Default constructor.
+ */
+ public EvalPropertyTag()

{ + }

+
+ /**
+ * Reads a value from the performs an EL evaluation and sets a variable.
+ *
+ * @return always

{@link #EVAL_PAGE}

.
+ */
+ public int doEndTag() throws JspException {
+ try {
+ final ServletRequest request = pageContext.getRequest();
+ final SlingBindings bindings = (SlingBindings)request.getAttribute(SlingBindings.class.getName());
+ final SlingScriptHelper scriptHelper = bindings.getSling();
+ final Resource baseResource = scriptHelper.getRequest().getResource();
+ final ResourceResolver resourceResolver = baseResource.getResourceResolver();
+
+ final Resource resource = resourceResolver.getResource(baseResource, this.path);
+ if (resource == null)

{ + throw new JspException("Resource not found: " + this.path); + }

+
+ final Node node = resource.adaptTo(Node.class);
+ if (node == null)

{ + throw new JspException("Path is not a valid node: " + this.path); + }

+
+ final Property propNode = node.getProperty(this.property);
+ if (propNode == node)

{ + throw new JspException("Property not found: " + this.path); + }

+
+
+ final String elValue = propNode.getString();
+ if (elValue != null) {
+ ELContext elctx = pageContext.getELContext();
+ String strValue = (String) getExpressionFactory().createValueExpression(elctx, elValue, String.class).getValue(elctx);
+
+ if (this.var == null || this.var.trim().equals(""))

{ + pageContext.getOut().print(strValue); + }

else

{ + pageContext.setAttribute(this.var, strValue); + }

+ }
+
+ return EVAL_PAGE;
+ } catch (PathNotFoundException e)

{ + throw new JspException(e); + } catch (RepositoryException e) {+ throw new JspException(e);+ }

catch (IOException e)

{ + throw new JspException(e); + }

+ }
+
+ // -------------------------< setter methods >---------------------------
+
+ public void setVar(String var)

{ + this.var = var; + }

+
+ public void setPath(String path)

{ + this.path = path; + }

+
+ public void setProperty(String property)

{ + this.property = property; + }

+
+ private ExpressionFactory getExpressionFactory()

{ + return JspFactory.getDefaultFactory() + .getJspApplicationContext(pageContext.getServletContext()) + .getExpressionFactory(); + + }

+}
diff -Nur jsp-taglib-base/src/main/resources/META-INF/taglib.tld jsp-taglib-update/src/main/resources/META-INF/taglib.tld
— jsp-taglib-base/src/main/resources/META-INF/taglib.tld 2008-07-22 20:21:56.000000000 -0700
+++ jsp-taglib-update/src/main/resources/META-INF/taglib.tld 2008-07-22 20:25:57.000000000 -0700
@@ -161,4 +161,43 @@
</attribute>
</tag>

+ <tag>
+ <description>
+ Performs an EL evaluation on the value in a JCR property.
+ </description>
+ <name>evalProperty</name>
+ <tag-class>
+ org.apache.sling.scripting.jsp.taglib.EvalPropertyTag
+ </tag-class>
+ <tei-class>
+ org.apache.sling.scripting.jsp.taglib.EvalPropertyTEI
+ </tei-class>
+ <body-content>empty</body-content>
+ <attribute>
+ <description>
+ The variable which receives the result of the evaluation.
+ If this attribute is missing or blank the result is written to out.
+ </description>
+ <name>var</name>
+ <required>false</required>
+ <rtexprvalue>false</rtexprvalue>
+ </attribute>
+ <attribute>
+ <description>
+ The relative path to the node which has the property to be evaluated.
+ If omitted the tag will use "." (current content node).
+ </description>
+ <name>path</name>
+ <required>false</required>
+ <rtexprvalue>true</rtexprvalue>
+ </attribute>
+ <attribute>
+ <description>
+ The property to be evaluated.
+ </description>
+ <name>property</name>
+ <required>true</required>
+ <rtexprvalue>true</rtexprvalue>
+ </attribute>
+ </tag>
</taglib>

Issue Links

• is superceded by: SLING-1500 Patch Submission: Expression Language (EL) Functions for JSP Taglib