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https://issues.apache.org/jira/browse/SLING-577?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12615924#action_12615924
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Tobias Bocanegra commented on SLING-577:
----------------------------------------
this is already possible when using JSTL and binding the properties (i.e
resource.adaptTo(ValueMap.class) to the page context.
directly accessing the DB is discouraged since all content should come from the
repository.
> Patch Submission: JSP tag to evaluate JCR properties using EL
> -------------------------------------------------------------
>
> Key: SLING-577
> URL: https://issues.apache.org/jira/browse/SLING-577
> Project: Sling
> Issue Type: New Feature
> Components: Scripting JSP
> Reporter: David Trott
> Attachments: evalproperty.patch
>
>
> 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 [EMAIL PROTECTED] #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>
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