A first stab at issue apache#3454

assemblies/plugins/pom.xml

@@ -714,6 +714,13 @@
             <version>${project.version}</version>
             <type>zip</type>
         </dependency>
+        <dependency>
+            <groupId>org.apache.hop</groupId>
+            <artifactId>hop-resolvers-pipeline</artifactId>
+            <version>2.12.0-SNAPSHOT</version>
+            <type>zip</type>
+        </dependency>
+
         <dependency>
             <groupId>org.apache.hop</groupId>
             <artifactId>hop-tech-avro</artifactId>

core/src/main/java/org/apache/hop/core/HopClientEnvironment.java

@@ -39,6 +39,7 @@
 import org.apache.hop.core.plugins.PluginRegistry;
 import org.apache.hop.core.row.value.ValueMetaPluginType;
 import org.apache.hop.core.util.EnvUtil;
+import org.apache.hop.core.variables.resolver.VariableResolverPluginType;
 import org.apache.hop.core.vfs.HopVfs;
 import org.apache.hop.core.vfs.plugin.VfsPluginType;
 
@@ -80,6 +81,7 @@ public static synchronized void init() throws HopException {
             DatabasePluginType.getInstance(),
             ExtensionPointPluginType.getInstance(),
             TwoWayPasswordEncoderPluginType.getInstance(),
+            VariableResolverPluginType.getInstance(),
             VfsPluginType.getInstance()));
   }
 

core/src/main/java/org/apache/hop/core/util/StringUtil.java

@@ -51,6 +51,10 @@ public class StringUtil {
 
   public static final String FIELD_CLOSE = "}";
 
+  public static final String RESOLVER_OPEN = "#{";
+
+  public static final String RESOLVER_CLOSE = "}";
+
   public static final String CRLF = "\r\n";
 
   public static final String INDENTCHARS = "                    ";

core/src/main/java/org/apache/hop/core/variables/Variables.java

@@ -25,11 +25,16 @@
 import java.util.Set;
 import org.apache.hop.core.Const;
 import org.apache.hop.core.config.HopConfig;
+import org.apache.hop.core.exception.HopException;
 import org.apache.hop.core.exception.HopValueException;
 import org.apache.hop.core.row.IRowMeta;
 import org.apache.hop.core.row.value.ValueMetaBase;
 import org.apache.hop.core.util.StringUtil;
 import org.apache.hop.core.util.Utils;
+import org.apache.hop.core.variables.resolver.VariableResolver;
+import org.apache.hop.metadata.api.IHopMetadataSerializer;
+import org.apache.hop.metadata.serializer.multi.MultiMetadataProvider;
+import org.apache.hop.metadata.util.HopMetadataInstance;
 
 /** This class is an implementation of IVariables */
 public class Variables implements IVariables {
@@ -139,11 +144,84 @@ public synchronized void setVariable(String variableName, String variableValue)
 
   @Override
   public synchronized String resolve(String aString) {
-    if (aString == null || aString.length() == 0) {
+    if (aString == null || aString.isEmpty()) {
       return aString;
     }
 
-    return StringUtil.environmentSubstitute(aString, properties);
+    String resolved = StringUtil.environmentSubstitute(aString, properties);
+
+    resolved = substituteVariableResolvers(resolved);
+
+    return resolved;
+  }
+
+  private String substituteVariableResolvers(String input) {
+    String resolved = input;
+    int startIndex = 0;
+    while (startIndex < resolved.length()) {
+      int resolverIndex = resolved.indexOf(StringUtil.RESOLVER_OPEN);
+      if (resolverIndex < 0) {
+        // There's nothing more to do here.
+        //
+        return resolved;
+      }
+
+      // Is there a close token?
+      //
+      int closeIndex = resolved.indexOf(StringUtil.RESOLVER_CLOSE, resolverIndex);
+      if (closeIndex < 0) {
+        // False positive on the open token
+        //
+        return resolved;
+      }
+
+      // The variable resolver String [resolverIndex, closeIndex$]
+      // is in the format: #{name:argument}
+      //
+      int colonIndex = resolved.indexOf(':', resolverIndex);
+      String name;
+      String argument;
+      if (colonIndex >= 0) {
+        name = resolved.substring(resolverIndex + StringUtil.RESOLVER_OPEN.length(), colonIndex);
+        argument = resolved.substring(colonIndex + 1, closeIndex);
+      } else {
+        name = resolved.substring(resolverIndex + StringUtil.RESOLVER_OPEN.length(), closeIndex);
+        argument = "";
+      }
+
+      try {
+        MultiMetadataProvider provider = HopMetadataInstance.getMetadataProvider();
+        IHopMetadataSerializer<VariableResolver> serializer =
+            provider.getSerializer(VariableResolver.class);
+
+        // This next loadA() method is relatively slow since it needs to go to disk.
+        //
+        VariableResolver resolver = serializer.load(name);
+        if (resolver == null) {
+          // return resolved;
+          //
+          throw new HopException(
+              "Variable Resolver '" + name + "' could not be found in the metadata");
+        }
+        String resolvedArgument = resolver.getIResolver().resolve(argument, this);
+
+        // We take the first part of the original resolved string, the resolved argument, and the
+        // last part
+        // to continue resolving all expressions in the string.
+        //
+        String before = resolved.substring(0, resolverIndex);
+        String after = resolved.substring(closeIndex + 1);
+        resolved = before + resolvedArgument + after;
+
+        // Where do we continue?
+        startIndex = before.length() + resolvedArgument.length();
+
+      } catch (HopException e) {
+        throw new RuntimeException(
+            "Error resolving variable '" + input + "' with variable resolver metadata", e);
+      }
+    }
+    return resolved;
   }
 
   /**

core/src/main/java/org/apache/hop/core/variables/resolver/IVariableResolver.java

@@ -0,0 +1,47 @@
+/*
+ * 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.hop.core.variables.resolver;
+
+import org.apache.hop.core.exception.HopException;
+import org.apache.hop.core.variables.IVariables;
+import org.apache.hop.metadata.api.HopMetadataObject;
+
+/** Indicates that the class can resolve variables in a specific manner. */
+@HopMetadataObject(objectFactory = VariableResolverObjectFactory.class)
+public interface IVariableResolver {
+  void init();
+
+  /**
+   * Resolve the variables in the given String.
+   *
+   * @param string The String in which we want to replace variables.
+   * @param variables The variables and values to use as a reference
+   * @return The input string with expressions resolved.
+   * @throws HopException In case something goes wrong.
+   */
+  String resolve(String string, IVariables variables) throws HopException;
+
+  void setPluginId();
+
+  String getPluginId();
+
+  void setPluginName(String pluginName);
+
+  String getPluginName();
+}

core/src/main/java/org/apache/hop/core/variables/resolver/VariableResolver.java

@@ -0,0 +1,53 @@
+/*
+ * 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.hop.core.variables.resolver;
+
+import lombok.Getter;
+import lombok.Setter;
+import org.apache.hop.metadata.api.HopMetadata;
+import org.apache.hop.metadata.api.HopMetadataBase;
+import org.apache.hop.metadata.api.HopMetadataProperty;
+import org.apache.hop.metadata.api.HopMetadataPropertyType;
+import org.apache.hop.metadata.api.IHopMetadata;
+
+@HopMetadata(
+    key = "variable-resolver",
+    name = "i18n::VariableResolver.name",
+    description = "i18n::VariableResolver.Description",
+    image = "ui/images/variable.svg",
+    documentationUrl = "/metadata-types/variable-resolver.html",
+    hopMetadataPropertyType = HopMetadataPropertyType.RDBMS_CONNECTION)
+@Getter
+@Setter
+public class VariableResolver extends HopMetadataBase implements IHopMetadata {
+  public static final String GUI_PLUGIN_ELEMENT_PARENT_ID =
+      "VariableResolver-PluginSpecific-Options";
+
+  @HopMetadataProperty private String description;
+
+  @HopMetadataProperty(key = "variable-resolver")
+  private IVariableResolver iResolver;
+
+  public String getPluginName() {
+    if (iResolver == null) {
+      return null;
+    }
+    return iResolver.getPluginName();
+  }
+}

core/src/main/java/org/apache/hop/core/variables/resolver/VariableResolverObjectFactory.java

@@ -0,0 +1,43 @@
+/*
+ * 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.hop.core.variables.resolver;
+
+import org.apache.hop.core.exception.HopException;
+import org.apache.hop.core.plugins.IPlugin;
+import org.apache.hop.core.plugins.PluginRegistry;
+import org.apache.hop.metadata.api.IHopMetadataObjectFactory;
+
+public class VariableResolverObjectFactory implements IHopMetadataObjectFactory {
+
+  @Override
+  public Object createObject(String id, Object parentObject) throws HopException {
+    PluginRegistry registry = PluginRegistry.getInstance();
+    IPlugin plugin = registry.findPluginWithId(VariableResolverPluginType.class, id);
+    return registry.loadClass(plugin);
+  }
+
+  @Override
+  public String getObjectId(Object object) throws HopException {
+    if (!(object instanceof IVariableResolver)) {
+      throw new HopException(
+          "Object is not of class IVariableResolver but of " + object.getClass().getName() + "'");
+    }
+    return ((IVariableResolver) object).getPluginId();
+  }
+}

core/src/main/java/org/apache/hop/core/variables/resolver/VariableResolverPlugin.java

@@ -0,0 +1,54 @@
+/*
+ * 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.hop.core.variables.resolver;
+
+import java.lang.annotation.Documented;
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+/** This annotation indicates that the given plugin is a variable resolver plugin. */
+@Documented
+@Retention(RetentionPolicy.RUNTIME)
+@Target(ElementType.TYPE)
+public @interface VariableResolverPlugin {
+  /**
+   * @return The ID of the password encoder plugin. You can specify more than one ID in a comma
+   *     separated format: id1,id2,id3 for deprecation purposes.
+   */
+  String id();
+
+  String name();
+
+  String description() default "";
+
+  /**
+   * @return True if a separate class loader is needed every time this class is instantiated
+   */
+  boolean isSeparateClassLoaderNeeded() default false;
+
+  String documentationUrl() default "";
+
+  String casesUrl() default "";
+
+  String forumUrl() default "";
+
+  String classLoaderGroup() default "";
+}