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    <p>There's quite a bunch of EL engines, of which most implement Java Expression Language API.</p> <ul> <li><p>Commons EL (<a href="http://jakarta.apache.org/commons/el/" rel="nofollow noreferrer">http://jakarta.apache.org/commons/el/</a>) Implementation of the JSP EL API that's existed forever. This library can be found in many JSP containers (Tomcat for example) or used as a foundation for within many vendor's J2EE servers.</p></li> <li><p>OGNL (<a href="http://www.ognl.org/" rel="nofollow noreferrer">http://www.ognl.org/</a>) One of the most expressive ELs available today and widely used with WebWork (Struts 2) and Tapestry.</p></li> <li><p>MVEL (<a href="https://github.com/mvel/mvel" rel="nofollow noreferrer">https://github.com/mvel/mvel</a>) A newcomer to EL which is part of the MVFlex/Valhalla project. Features look more in line with OGNL's offering with method invocation and some interesting regular expression support.</p></li> <li><p>(Unified) Expression Language (<a href="https://jcp.org/aboutJava/communityprocess/final/jsr341/index.html" rel="nofollow noreferrer">https://jcp.org/aboutJava/communityprocess/final/jsr341/index.html</a> and <a href="http://jcp.org/en/jsr/detail?id=245" rel="nofollow noreferrer">http://jcp.org/en/jsr/detail?id=245</a>) Standard expression language first introduced in Java EE 5 (EL 2.1) and enhanced in Java EE 6 (EL 2.2) and Java EE 7 (EL 3.0). Reference implementation available from Glassfish project - <a href="https://uel.java.net/" rel="nofollow noreferrer"> Unified Expression Language</a>.</p></li> <li><p>JEXL (<a href="http://jakarta.apache.org/commons/jexl/" rel="nofollow noreferrer">http://jakarta.apache.org/commons/jexl/</a>) An implementation based on Velocity's parser. Because of this, it acts more like a limited templating solution with things like method invocation.</p></li> </ul> <p><em><a href="https://weblogs.java.net/blog/jhook/archive/2006/11/el_comparisons.html" rel="nofollow noreferrer">Source</a></em></p> <p>For now I ended up with this code using <strong>BeanUtils</strong> - ugly but works.</p> <pre><code>import java.lang.reflect.InvocationTargetException; import java.util.Map; import java.util.NoSuchElementException; import java.util.StringTokenizer; import org.apache.commons.beanutils.PropertyUtils; import org.apache.commons.lang.StringUtils; import org.slf4j.LoggerFactory; public static class SimpleEvaluator implements IExprLangEvaluator { private static final org.slf4j.Logger log = LoggerFactory.getLogger( SimpleEvaluator.class ); @Override public String evaluateEL( String template, Map&lt;String, String&gt; properties ) { StringTokenizer st = new StringTokenizer( template ); String text = st.nextToken("${"); StringBuilder sb = new StringBuilder(); // Parse the template: "Hello ${person.name} ${person.surname}, ${person.age}!" do{ try { sb.append(text); if( ! st.hasMoreTokens() ) break; // "${foo.bar[a]" String expr = st.nextToken("}"); // "foo.bar[a].baz" expr = expr.substring(2); // "foo" String var = StringUtils.substringBefore( expr, "."); Object subject = properties.get( var ); // "bar[a].baz" String propPath = StringUtils.substringAfter( expr, "."); sb.append( resolveProperty( subject, propPath ) ); text = st.nextToken("${"); text = text.substring(1); } catch( NoSuchElementException ex ){ // Unclosed ${ log.warn("Unclosed ${ expression, missing } : " + template); } } while( true ); return sb.toString(); } // BeanUtils private String resolveProperty( Object subject, String propPath ) { if( subject == null ) return ""; if( propPath == null || propPath.isEmpty() ) return subject.toString(); try { return "" + PropertyUtils.getProperty( subject, propPath ); } catch( IllegalAccessException | InvocationTargetException | NoSuchMethodException ex ) { log.warn("Failed resolving '" + propPath + "' on " + subject + ":\n " + ex.getMessage(), ex); return ""; } } }// class SimpleEvaluator </code></pre>
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