Moved variable name extraction to separate class.

Change-Id: Ic4105f9f3557c924928321c1b27f7b0e3444bfbc
Issue-ID: SO-374
Signed-off-by: biniek <lukasz.biniek@nokia.com>

4 files changed, 581 insertions, 500 deletions

diff --git a/bpmn/MSOCoreBPMN/pom.xml b/bpmn/MSOCoreBPMN/pom.xml
index b3eddeda41..6884c1e33b 100644
--- a/bpmn/MSOCoreBPMN/pom.xml
+++ b/bpmn/MSOCoreBPMN/pom.xml
@@ -167,5 +167,11 @@
             <artifactId>status-control</artifactId>
             <version>${project.version}</version>
         </dependency>
+        <dependency>
+            <groupId>org.assertj</groupId>
+            <artifactId>assertj-core</artifactId>
+            <version>3.8.0</version>
+            <scope>test</scope>
+        </dependency>
     </dependencies>
 </project>
diff --git a/bpmn/MSOCoreBPMN/src/main/java/org/openecomp/mso/bpmn/core/BaseTask.java b/bpmn/MSOCoreBPMN/src/main/java/org/openecomp/mso/bpmn/core/BaseTask.java
index e9da2355e4..77e418d4c3 100644
--- a/bpmn/MSOCoreBPMN/src/main/java/org/openecomp/mso/bpmn/core/BaseTask.java
+++ b/bpmn/MSOCoreBPMN/src/main/java/org/openecomp/mso/bpmn/core/BaseTask.java
@@ -23,510 +23,432 @@ package org.openecomp.mso.bpmn.core;
 import org.camunda.bpm.engine.delegate.DelegateExecution;
 import org.camunda.bpm.engine.delegate.Expression;
 import org.camunda.bpm.engine.delegate.JavaDelegate;
+import org.openecomp.mso.bpmn.core.internal.VariableNameExtractor;
 
 /**
  * Base class for service tasks.
  */
 public class BaseTask implements JavaDelegate {
 
-	/**
-	 * Get the value of a required field.  This method throws
-	 * MissingInjectedFieldException if the expression is null, and
-	 * BadInjectedFieldException if the expression evaluates to a null
-	 * value.
-	 *
-	 * @param expression the expression
-	 * @param execution the execution
-	 * @param fieldName the field name (for logging and exceptions)
-	 * @return the field value
-	 */
-	protected Object getField(Expression expression,
-			DelegateExecution execution, String fieldName) {
-		return getFieldImpl(expression, execution, fieldName, false);
-	}
-	
-	/**
-	 * Gets the value of an optional field.  There are three conditions
-	 * in which this method returns null:
-	 * <p>
-	 * <ol>
-	 * <li> The expression itself is null (i.e. the field is missing
-	 * altogether.</li>
-	 * <li>The expression evaluates to a null value.</li>
-	 * <li>The expression references a single variable which has not
-	 * been set.</li>
-	 * </ol>
-	 * <p>
-	 * Examples:<br>
-	 * Expression ${x} when x is null: return null<br>
-	 * Expression ${x} when x is unset: return null<br>
-	 * Expression ${x+y} when x and/or y are unset: exception<br>
-	 * 
-	 * @param expression the expression
-	 * @param execution the execution
-	 * @param fieldName the field name (for logging and exceptions)
-	 * @return the field value, possibly null
-	 */
-	protected Object getOptionalField(Expression expression,
-			DelegateExecution execution, String fieldName) {
-		return getFieldImpl(expression, execution, fieldName, true);
-	}
-	
-	/**
-	 * Get the value of a required output variable field. This method
-	 * throws MissingInjectedFieldException if the expression is null, and
-	 * BadInjectedFieldException if the expression produces a null or
-	 * illegal variable name.  Legal variable names contain only letters,
-	 * numbers, and the underscore character ('_').
-	 *
-	 * @param expression the expression
-	 * @param execution the execution
-	 * @param fieldName the field name (for logging and exceptions)
-	 * @return the output variable name
-	 */
-	protected String getOutputField(Expression expression,
-			DelegateExecution execution, String fieldName) {
-		Object o = getFieldImpl(expression, execution, fieldName, false);
-		if (o instanceof String) {
-			String variable = (String) o;
-			if (!isLegalVariable(variable)) {
-				throw new BadInjectedFieldException(
-					fieldName, getTaskName(), "'" + variable
-						+ "' is not a legal variable name");
-			}
-			return variable;
-		} else {
-			throw new BadInjectedFieldException(
-				fieldName, getTaskName(), "expected a variable name string"
-					+ ", got object of type " + o.getClass().getName());
-		}
-	}
-	
-	/**
-	 * Get the value of an optional output variable field. This method
-	 * throws BadInjectedFieldException if the expression produces an illegal
-	 * variable name.  Legal variable names contain only letters, numbers,
-	 * and the underscore character ('_').
-	 * 
-	 * @param expression the expression
-	 * @param execution the execution
-	 * @param fieldName the field name (for logging and exceptions)
-	 * @return the output variable name, possibly null
-	 */
-	protected String getOptionalOutputField(Expression expression,
-			DelegateExecution execution, String fieldName) {
-		Object o = getFieldImpl(expression, execution, fieldName, true);
-		if (o instanceof String) {
-			String variable = (String) o;
-			if (!isLegalVariable(variable)) {
-				throw new BadInjectedFieldException(
-					fieldName, getTaskName(), "'" + variable
-						+ "' is not a legal variable name");
-			}
-			return variable;
-		} else if (o == null) {
-			return null;
-		} else {
-			throw new BadInjectedFieldException(
-				fieldName, getTaskName(), "expected a variable name string"
-					+ ", got object of type " + o.getClass().getName());
-		}
-	}
-
-	/**
-	 * Get the value of a required string field.  This method throws
-	 * MissingInjectedFieldException if the expression is null, and
-	 * BadInjectedFieldException if the expression evaluates to a null
-	 * value.
-	 * <p>
-	 * Note: the result is coerced to a string value, if necessary.
-	 *
-	 * @param expression the expression
-	 * @param execution the execution
-	 * @param fieldName the field name (for logging and exceptions)
-	 * @return the field value
-	 */
-	protected String getStringField(Expression expression,
-			DelegateExecution execution, String fieldName) {
-		Object o = getFieldImpl(expression, execution, fieldName, false);
-		if (o instanceof String) {
-			return (String) o;
-		} else {
-			throw new BadInjectedFieldException(
-				fieldName, getTaskName(), "cannot convert '" + o.toString()
-				+ "' to Integer");
-		}
-	}
-	
-	/**
-	 * Gets the value of an optional string field.  There are three conditions
-	 * in which this method returns null:
-	 * <p>
-	 * <ol>
-	 * <li> The expression itself is null (i.e. the field is missing
-	 * altogether.</li>
-	 * <li>The expression evaluates to a null value.</li>
-	 * <li>The expression references a single variable which has not
-	 * been set.</li>
-	 * </ol>
-	 * <p>
-	 * Examples:<br>
-	 * Expression ${x} when x is null: return null<br>
-	 * Expression ${x} when x is unset: return null<br>
-	 * Expression ${x+y} when x and/or y are unset: exception<br>
-	 * <p>
-	 * Note: the result is coerced to a string value, if necessary.
-	 * 
-	 * @param expression the expression
-	 * @param execution the execution
-	 * @param fieldName the field name (for logging and exceptions)
-	 * @return the field value, possibly null
-	 */
-	protected String getOptionalStringField(Expression expression,
-			DelegateExecution execution, String fieldName) {
-		Object o = getFieldImpl(expression, execution, fieldName, true);
-		if (o instanceof String) {
-			return (String) o;
-		} else if (o == null) {
-			return null;
-		} else {
-			return o.toString();
-		}
-	}
-	
-	/**
-	 * Get the value of a required integer field. This method throws
-	 * MissingInjectedFieldException if the expression is null, and
-	 * BadInjectedFieldException if the expression evaluates to a null
-	 * value or a value that cannot be coerced to an integer.
-	 *
-	 * @param expression the expression
-	 * @param execution the execution
-	 * @param fieldName the field name (for logging and exceptions)
-	 * @return the field value
-	 */
-	protected Integer getIntegerField(Expression expression,
-			DelegateExecution execution, String fieldName) {
-		Object o = getFieldImpl(expression, execution, fieldName, false);
-		if (o instanceof Integer) {
-			return (Integer) o;
-		} else {
-			try {
-				return Integer.parseInt(o.toString());
-			} catch (NumberFormatException e) {
-				throw new BadInjectedFieldException(
-					fieldName, getTaskName(), "cannot convert '" + o.toString()
-					+ "' to Integer");
-			}
-		}
-	}
-	
-	/**
-	 * Gets the value of an optional integer field.  There are three conditions
-	 * in which this method returns null:
-	 * <p>
-	 * <ol>
-	 * <li> The expression itself is null (i.e. the field is missing
-	 * altogether.</li>
-	 * <li>The expression evaluates to a null value.</li>
-	 * <li>The expression references a single variable which has not
-	 * been set.</li>
-	 * </ol>
-	 * <p>
-	 * Examples:<br>
-	 * Expression ${x} when x is null: return null<br>
-	 * Expression ${x} when x is unset: return null<br>
-	 * Expression ${x+y} when x and/or y are unset: exception<br>
-	 * <p>
-	 * Note: the result is coerced to an integer value, if necessary. This
-	 * method throws BadInjectedFieldException if the result cannot be coerced
-	 * to an integer.
-	 * 
-	 * @param expression the expression
-	 * @param execution the execution
-	 * @param fieldName the field name (for logging and exceptions)
-	 * @return the field value, possibly null
-	 */
-	protected Integer getOptionalIntegerField(Expression expression,
-			DelegateExecution execution, String fieldName) {
-		Object o = getFieldImpl(expression, execution, fieldName, true);
-		if (o instanceof Integer) {
-			return (Integer) o;
-		} else if (o == null) {
-			return null;
-		} else {
-			try {
-				return Integer.parseInt(o.toString());
-			} catch (NumberFormatException e) {
-				throw new BadInjectedFieldException(
-					fieldName, getTaskName(), "cannot convert '" + o.toString()
-					+ "' to Integer");
-			}
-		}
-	}
-	
-	/**
-	 * Gets the value of an optional long field.  There are three conditions
-	 * in which this method returns null:
-	 * <p>
-	 * <ol>
-	 * <li> The expression itself is null (i.e. the field is missing
-	 * altogether.</li>
-	 * <li>The expression evaluates to a null value.</li>
-	 * <li>The expression references a single variable which has not
-	 * been set.</li>
-	 * </ol>
-	 * <p>
-	 * Examples:<br>
-	 * Expression ${x} when x is null: return null<br>
-	 * Expression ${x} when x is unset: return null<br>
-	 * Expression ${x+y} when x and/or y are unset: exception<br>
-	 * <p>
-	 * Note: the result is coerced to a long value, if necessary. This
-	 * method throws BadInjectedFieldException if the result cannot be coerced
-	 * to a long.
-	 * 
-	 * @param expression the expression
-	 * @param execution the execution
-	 * @param fieldName the field name (for logging and exceptions)
-	 * @return the field value, possibly null
-	 */
-	protected Long getOptionalLongField(Expression expression,
-			DelegateExecution execution, String fieldName) {
-		Object o = getFieldImpl(expression, execution, fieldName, true);
-		if (o instanceof Long) {
-			return (Long) o;
-		} else if (o == null) {
-			return null;
-		} else {
-			try {
-				return Long.parseLong(o.toString());
-			} catch (NumberFormatException e) {
-				throw new BadInjectedFieldException(
-					fieldName, getTaskName(), "cannot convert '" + o.toString()
-					+ "' to Long");
-			}
-		}
-	}
-	
-	/**
-	 * Get the value of a required long field. This method throws
-	 * MissingInjectedFieldException if the expression is null, and
-	 * BadInjectedFieldException if the expression evaluates to a null
-	 * value or a value that cannot be coerced to a long.
-	 *
-	 * @param expression the expression
-	 * @param execution the execution
-	 * @param fieldName the field name (for logging and exceptions)
-	 * @return the field value
-	 */
-	protected Long getLongField(Expression expression,
-			DelegateExecution execution, String fieldName) {
-		Object o = getFieldImpl(expression, execution, fieldName, false);
-		if (o instanceof Long) {
-			return (Long) o;
-		} else {
-			try {
-				return Long.parseLong(o.toString());
-			} catch (NumberFormatException e) {
-				throw new BadInjectedFieldException(
-					fieldName, getTaskName(), "cannot convert '" + o.toString()
-					+ "' to Long");
-			}
-		}
-	}
-
-	/**
-	 * Common implementation for field "getter" methods.
-	 * @param expression the expression
-	 * @param execution the execution
-	 * @param fieldName the field name (for logging and exceptions)
-	 * @param optional true if the field is optional
-	 * @return the field value, possibly null
-	 */
-	private Object getFieldImpl(Expression expression,
-			DelegateExecution execution, String fieldName, boolean optional) {
-		if (expression == null) {
-			if (!optional) {
-				throw new MissingInjectedFieldException(
-					fieldName, getTaskName());
-			}
-			return null;
-		}
-
-		Object value;
-
-		try {
-			value = expression.getValue(execution);
-		} catch (Exception e) {
-			if (!optional) {
-				throw new BadInjectedFieldException(
-					fieldName, getTaskName(), e.getClass().getSimpleName(), e);
-			}
-
-			// At this point, we have an exception that occurred while
-			// evaluating an expression for an optional field. A common 
-			// problem is that the expression is a simple reference to a
-			// variable which has never been set, e.g. the expression is
-			// ${x}. The normal activiti behavior is to throw an exception,
-			// but we don't like that, so we have the following workaround,
-			// which parses the expression text to see if it is a "simple"
-			// variable reference, and if so, returns null.  If the
-			// expression is anything other than a single variable
-			// reference, then an exception is thrown, as it would have
-			// been without this workaround.
-
-			// Get the expression text so we can parse it
-			String s = expression.getExpressionText();
-
-//			if (isDebugEnabled(execution)) {
-//				logDebug(execution, getTaskName() + " field '" + fieldName
-//					+ "' expression evaluation failed: " + s);
-//			}
-
-			int len = s.length();
-			int i = 0;
-
-			// Skip whitespace
-			while (i < len && Character.isWhitespace(s.charAt(i))) {
-				i++;
-			}
-
-			// Next character must be '$'
-			if (i == len || s.charAt(i++) != '$') {
-				throw new BadInjectedFieldException(
-					fieldName, getTaskName(), e.getClass().getSimpleName(), e);
-			}
-
-			// Skip whitespace
-			while (i < len && Character.isWhitespace(s.charAt(i))) {
-				i++;
-			}
-
-			// Next character must be '{'
-			if (i == len || s.charAt(i++) != '{') {
-				throw new BadInjectedFieldException(
-					fieldName, getTaskName(), e.getClass().getSimpleName(), e);
-			}
-
-			// Skip whitespace
-			while (i < len && Character.isWhitespace(s.charAt(i))) {
-				i++;
-			}
-
-			// Collect the variable name
-			StringBuilder variable = new StringBuilder();
-			while (i < len && isWordCharacter(s.charAt(i))) {
-				variable.append(s.charAt(i));
-				i++;
-			}
-
-			if (variable.length() == 0) {
-				throw new BadInjectedFieldException(
-					fieldName, getTaskName(), e.getClass().getSimpleName(), e);
-			}
-
-			// Skip whitespace
-			while (i < len && Character.isWhitespace(s.charAt(i))) {
-				i++;
-			}
-
-			// Next character must be '}'
-			if (i == len || s.charAt(i++) != '}') {
-				throw new BadInjectedFieldException(
-					fieldName, getTaskName(), e.getClass().getSimpleName(), e);
-			}
-
-			// Skip whitespace
-			while (i < len && Character.isWhitespace(s.charAt(i))) {
-				i++;
-			}
-
-			// Must be at end of string
-			if (i != len) {
-				throw new BadInjectedFieldException(
-					fieldName, getTaskName(), e.getClass().getSimpleName(), e);
-			}
-
-//			if (isDebugEnabled(execution)) {
-//				logDebug(execution, "Checking if variable '"
-//					+ variable.toString() + "' exists");
-//			}
-
-			// If the variable exists then the problem was
-			// something else...
-			if (execution.hasVariable(variable.toString())) {
-				throw new BadInjectedFieldException(
-					fieldName, getTaskName(), e.getClass().getSimpleName(), e);
-			}
-
-			// The variable doesn't exist.
-
-//			if (isDebugEnabled(execution)) {
-//				logDebug(execution, "Variable '" + variable.toString()
-//					+ "' does not exist [ok]");
-//			}
-
-			value = null;
-		}
-
-		if (value == null && !optional) {
-			throw new BadInjectedFieldException(
-				fieldName, getTaskName(), "required field has null value");
-		}
-	
-		return value;
-	}
-	
-	/**
-	 * Tests if a character is a "word" character.
-	 * @param c the character
-	 * @return true if the character is a "word" character.
-	 */
-	private boolean isWordCharacter(char c) {
-		return (Character.isLetterOrDigit(c) || c == '_');
-	}
-	
-	/**
-	 * Tests if the specified string is a legal flow variable name.
-	 * @param name the string
-	 * @return true if the string is a legal flow variable name
-	 */
-	private boolean isLegalVariable(String name) {
-		if (name == null) {
-			return false;
-		}
-
-		int len = name.length();
-
-		if (len == 0) {
-			return false;
-		}
-
-		char c = name.charAt(0);
-
-		if (!Character.isLetter(c) && c != '_') {
-			return false;
-		}
-
-		for (int i = 1; i < len; i++) {
-			c = name.charAt(i);
-			if (!Character.isLetterOrDigit(c) && c != '_') {
-				return false;
-			}
-		}
-
-		return true;
-	}
-	
-	/**
-	 * Returns the name of the task (normally the java class name).
-	 * @return the name of the task
-	 */
-	public String getTaskName() {
-		return getClass().getSimpleName();
-	}
-
-	@Override
-	public void execute(DelegateExecution execution) throws Exception {	}
+    /**
+     * Get the value of a required field.  This method throws
+     * MissingInjectedFieldException if the expression is null, and
+     * BadInjectedFieldException if the expression evaluates to a null
+     * value.
+     *
+     * @param expression the expression
+     * @param execution the execution
+     * @param fieldName the field name (for logging and exceptions)
+     * @return the field value
+     */
+    protected Object getField(Expression expression,
+            DelegateExecution execution, String fieldName) {
+        return getFieldImpl(expression, execution, fieldName, false);
+    }
+
+    /**
+     * Gets the value of an optional field.  There are three conditions
+     * in which this method returns null:
+     * <p>
+     * <ol>
+     * <li> The expression itself is null (i.e. the field is missing
+     * altogether.</li>
+     * <li>The expression evaluates to a null value.</li>
+     * <li>The expression references a single variable which has not
+     * been set.</li>
+     * </ol>
+     * <p>
+     * Examples:<br>
+     * Expression ${x} when x is null: return null<br>
+     * Expression ${x} when x is unset: return null<br>
+     * Expression ${x+y} when x and/or y are unset: exception<br>
+     *
+     * @param expression the expression
+     * @param execution the execution
+     * @param fieldName the field name (for logging and exceptions)
+     * @return the field value, possibly null
+     */
+    protected Object getOptionalField(Expression expression,
+            DelegateExecution execution, String fieldName) {
+        return getFieldImpl(expression, execution, fieldName, true);
+    }
+
+    /**
+     * Get the value of a required output variable field. This method
+     * throws MissingInjectedFieldException if the expression is null, and
+     * BadInjectedFieldException if the expression produces a null or
+     * illegal variable name.  Legal variable names contain only letters,
+     * numbers, and the underscore character ('_').
+     *
+     * @param expression the expression
+     * @param execution the execution
+     * @param fieldName the field name (for logging and exceptions)
+     * @return the output variable name
+     */
+    protected String getOutputField(Expression expression,
+            DelegateExecution execution, String fieldName) {
+        Object o = getFieldImpl(expression, execution, fieldName, false);
+        if (o instanceof String) {
+            String variable = (String) o;
+            if (!isLegalVariable(variable)) {
+                throw new BadInjectedFieldException(
+                        fieldName, getTaskName(), "'" + variable
+                        + "' is not a legal variable name");
+            }
+            return variable;
+        } else {
+            throw new BadInjectedFieldException(
+                    fieldName, getTaskName(), "expected a variable name string"
+                    + ", got object of type " + o.getClass().getName());
+        }
+    }
+
+    /**
+     * Get the value of an optional output variable field. This method
+     * throws BadInjectedFieldException if the expression produces an illegal
+     * variable name.  Legal variable names contain only letters, numbers,
+     * and the underscore character ('_').
+     *
+     * @param expression the expression
+     * @param execution the execution
+     * @param fieldName the field name (for logging and exceptions)
+     * @return the output variable name, possibly null
+     */
+    protected String getOptionalOutputField(Expression expression,
+            DelegateExecution execution, String fieldName) {
+        Object o = getFieldImpl(expression, execution, fieldName, true);
+        if (o instanceof String) {
+            String variable = (String) o;
+            if (!isLegalVariable(variable)) {
+                throw new BadInjectedFieldException(
+                        fieldName, getTaskName(), "'" + variable
+                        + "' is not a legal variable name");
+            }
+            return variable;
+        } else if (o == null) {
+            return null;
+        } else {
+            throw new BadInjectedFieldException(
+                    fieldName, getTaskName(), "expected a variable name string"
+                    + ", got object of type " + o.getClass().getName());
+        }
+    }
+
+    /**
+     * Get the value of a required string field.  This method throws
+     * MissingInjectedFieldException if the expression is null, and
+     * BadInjectedFieldException if the expression evaluates to a null
+     * value.
+     * <p>
+     * Note: the result is coerced to a string value, if necessary.
+     *
+     * @param expression the expression
+     * @param execution the execution
+     * @param fieldName the field name (for logging and exceptions)
+     * @return the field value
+     */
+    protected String getStringField(Expression expression,
+            DelegateExecution execution, String fieldName) {
+        Object o = getFieldImpl(expression, execution, fieldName, false);
+        if (o instanceof String) {
+            return (String) o;
+        } else {
+            throw new BadInjectedFieldException(
+                    fieldName, getTaskName(), "cannot convert '" + o.toString()
+                    + "' to Integer");
+        }
+    }
+
+    /**
+     * Gets the value of an optional string field.  There are three conditions
+     * in which this method returns null:
+     * <p>
+     * <ol>
+     * <li> The expression itself is null (i.e. the field is missing
+     * altogether.</li>
+     * <li>The expression evaluates to a null value.</li>
+     * <li>The expression references a single variable which has not
+     * been set.</li>
+     * </ol>
+     * <p>
+     * Examples:<br>
+     * Expression ${x} when x is null: return null<br>
+     * Expression ${x} when x is unset: return null<br>
+     * Expression ${x+y} when x and/or y are unset: exception<br>
+     * <p>
+     * Note: the result is coerced to a string value, if necessary.
+     *
+     * @param expression the expression
+     * @param execution the execution
+     * @param fieldName the field name (for logging and exceptions)
+     * @return the field value, possibly null
+     */
+    protected String getOptionalStringField(Expression expression,
+            DelegateExecution execution, String fieldName) {
+        Object o = getFieldImpl(expression, execution, fieldName, true);
+        if (o instanceof String) {
+            return (String) o;
+        } else if (o == null) {
+            return null;
+        } else {
+            return o.toString();
+        }
+    }
+
+    /**
+     * Get the value of a required integer field. This method throws
+     * MissingInjectedFieldException if the expression is null, and
+     * BadInjectedFieldException if the expression evaluates to a null
+     * value or a value that cannot be coerced to an integer.
+     *
+     * @param expression the expression
+     * @param execution the execution
+     * @param fieldName the field name (for logging and exceptions)
+     * @return the field value
+     */
+    protected Integer getIntegerField(Expression expression,
+            DelegateExecution execution, String fieldName) {
+        Object o = getFieldImpl(expression, execution, fieldName, false);
+        if (o instanceof Integer) {
+            return (Integer) o;
+        } else {
+            try {
+                return Integer.parseInt(o.toString());
+            } catch (NumberFormatException e) {
+                throw new BadInjectedFieldException(
+                        fieldName, getTaskName(), "cannot convert '" + o.toString()
+                        + "' to Integer");
+            }
+        }
+    }
+
+    /**
+     * Gets the value of an optional integer field.  There are three conditions
+     * in which this method returns null:
+     * <p>
+     * <ol>
+     * <li> The expression itself is null (i.e. the field is missing
+     * altogether.</li>
+     * <li>The expression evaluates to a null value.</li>
+     * <li>The expression references a single variable which has not
+     * been set.</li>
+     * </ol>
+     * <p>
+     * Examples:<br>
+     * Expression ${x} when x is null: return null<br>
+     * Expression ${x} when x is unset: return null<br>
+     * Expression ${x+y} when x and/or y are unset: exception<br>
+     * <p>
+     * Note: the result is coerced to an integer value, if necessary. This
+     * method throws BadInjectedFieldException if the result cannot be coerced
+     * to an integer.
+     *
+     * @param expression the expression
+     * @param execution the execution
+     * @param fieldName the field name (for logging and exceptions)
+     * @return the field value, possibly null
+     */
+    protected Integer getOptionalIntegerField(Expression expression,
+            DelegateExecution execution, String fieldName) {
+        Object o = getFieldImpl(expression, execution, fieldName, true);
+        if (o instanceof Integer) {
+            return (Integer) o;
+        } else if (o == null) {
+            return null;
+        } else {
+            try {
+                return Integer.parseInt(o.toString());
+            } catch (NumberFormatException e) {
+                throw new BadInjectedFieldException(
+                        fieldName, getTaskName(), "cannot convert '" + o.toString()
+                        + "' to Integer");
+            }
+        }
+    }
+
+    /**
+     * Gets the value of an optional long field.  There are three conditions
+     * in which this method returns null:
+     * <p>
+     * <ol>
+     * <li> The expression itself is null (i.e. the field is missing
+     * altogether.</li>
+     * <li>The expression evaluates to a null value.</li>
+     * <li>The expression references a single variable which has not
+     * been set.</li>
+     * </ol>
+     * <p>
+     * Examples:<br>
+     * Expression ${x} when x is null: return null<br>
+     * Expression ${x} when x is unset: return null<br>
+     * Expression ${x+y} when x and/or y are unset: exception<br>
+     * <p>
+     * Note: the result is coerced to a long value, if necessary. This
+     * method throws BadInjectedFieldException if the result cannot be coerced
+     * to a long.
+     *
+     * @param expression the expression
+     * @param execution the execution
+     * @param fieldName the field name (for logging and exceptions)
+     * @return the field value, possibly null
+     */
+    protected Long getOptionalLongField(Expression expression,
+            DelegateExecution execution, String fieldName) {
+        Object o = getFieldImpl(expression, execution, fieldName, true);
+        if (o instanceof Long) {
+            return (Long) o;
+        } else if (o == null) {
+            return null;
+        } else {
+            try {
+                return Long.parseLong(o.toString());
+            } catch (NumberFormatException e) {
+                throw new BadInjectedFieldException(
+                        fieldName, getTaskName(), "cannot convert '" + o.toString()
+                        + "' to Long");
+            }
+        }
+    }
+
+    /**
+     * Get the value of a required long field. This method throws
+     * MissingInjectedFieldException if the expression is null, and
+     * BadInjectedFieldException if the expression evaluates to a null
+     * value or a value that cannot be coerced to a long.
+     *
+     * @param expression the expression
+     * @param execution the execution
+     * @param fieldName the field name (for logging and exceptions)
+     * @return the field value
+     */
+    protected Long getLongField(Expression expression,
+            DelegateExecution execution, String fieldName) {
+        Object o = getFieldImpl(expression, execution, fieldName, false);
+        if (o instanceof Long) {
+            return (Long) o;
+        } else {
+            try {
+                return Long.parseLong(o.toString());
+            } catch (NumberFormatException e) {
+                throw new BadInjectedFieldException(
+                        fieldName, getTaskName(), "cannot convert '" + o.toString()
+                        + "' to Long");
+            }
+        }
+    }
+
+    /**
+     * Common implementation for field "getter" methods.
+     *
+     * @param expression the expression
+     * @param execution the execution
+     * @param fieldName the field name (for logging and exceptions)
+     * @param optional true if the field is optional
+     * @return the field value, possibly null
+     */
+    private Object getFieldImpl(Expression expression,
+            DelegateExecution execution, String fieldName, boolean optional) {
+        if (expression == null) {
+            if (!optional) {
+                throw new MissingInjectedFieldException(
+                        fieldName, getTaskName());
+            }
+            return null;
+        }
+
+        Object value = null;
+
+        try {
+            value = expression.getValue(execution);
+        } catch (Exception e) {
+            if (!optional) {
+                throw new BadInjectedFieldException(
+                        fieldName, getTaskName(), e.getClass().getSimpleName(), e);
+            }
+
+            // At this point, we have an exception that occurred while
+            // evaluating an expression for an optional field. A common
+            // problem is that the expression is a simple reference to a
+            // variable which has never been set, e.g. the expression is
+            // ${x}. The normal activiti behavior is to throw an exception,
+            // but we don't like that, so we have the following workaround,
+            // which parses the expression text to see if it is a "simple"
+            // variable reference, and if so, returns null.  If the
+            // expression is anything other than a single variable
+            // reference, then an exception is thrown, as it would have
+            // been without this workaround.
+
+            // Get the expression text so we can parse it
+            String s = expression.getExpressionText();
+            new VariableNameExtractor(s).extract().ifPresent(name -> {
+                if (execution.hasVariable(name)) {
+                    throw new BadInjectedFieldException(
+                            fieldName, getTaskName(), e.getClass().getSimpleName(), e);
+                }
+            });
+        }
+
+        if (value == null && !optional) {
+            throw new BadInjectedFieldException(
+                    fieldName, getTaskName(), "required field has null value");
+        }
+
+        return value;
+    }
+
+    /**
+     * Tests if a character is a "word" character.
+     *
+     * @param c the character
+     * @return true if the character is a "word" character.
+     */
+    private static boolean isWordCharacter(char c) {
+        return (Character.isLetterOrDigit(c) || c == '_');
+    }
+
+    /**
+     * Tests if the specified string is a legal flow variable name.
+     *
+     * @param name the string
+     * @return true if the string is a legal flow variable name
+     */
+    private boolean isLegalVariable(String name) {
+        if (name == null) {
+            return false;
+        }
+
+        int len = name.length();
+
+        if (len == 0) {
+            return false;
+        }
+
+        char c = name.charAt(0);
+
+        if (!Character.isLetter(c) && c != '_') {
+            return false;
+        }
+
+        for (int i = 1; i < len; i++) {
+            c = name.charAt(i);
+            if (!Character.isLetterOrDigit(c) && c != '_') {
+                return false;
+            }
+        }
+
+        return true;
+    }
+
+    /**
+     * Returns the name of the task (normally the java class name).
+     *
+     * @return the name of the task
+     */
+    public String getTaskName() {
+        return getClass().getSimpleName();
+    }
+
+    @Override
+    public void execute(DelegateExecution execution) throws Exception {
+    }
 }
diff --git a/bpmn/MSOCoreBPMN/src/main/java/org/openecomp/mso/bpmn/core/internal/VariableNameExtractor.java b/bpmn/MSOCoreBPMN/src/main/java/org/openecomp/mso/bpmn/core/internal/VariableNameExtractor.java
new file mode 100644
index 0000000000..e1aaba74da
--- /dev/null
+++ b/bpmn/MSOCoreBPMN/src/main/java/org/openecomp/mso/bpmn/core/internal/VariableNameExtractor.java
@@ -0,0 +1,67 @@
+/*-
+ * ============LICENSE_START=======================================================
+ * ONAP - SO
+ * ================================================================================
+ * Copyright (C) 2017 AT&T Intellectual Property. All rights reserved.
+ * ================================================================================
+ * Licensed 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.
+ * ============LICENSE_END=========================================================
+ */
+
+package org.openecomp.mso.bpmn.core.internal;
+
+import java.util.Optional;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+
+/**
+ * Extracts variable name from expression if entire expression is just
+ * one variable, for example "${x}".
+ *
+ * Ignores all whitespaces, except inside variable name.
+ *
+ * Examples:
+ * "${x}", extracted variable name is "x"
+ * " ${\t weird_NAME    }", extracted variable name is "weird_NAME"
+ * "${incorrect name}", no extracted name
+ * "${two}+${two}", no extracted name
+ */
+public class VariableNameExtractor {
+
+    private static final Pattern VARIABLE_NAME_PATTERN = Pattern
+            .compile("^\\s*\\$\\s*\\{\\s*([a-zA-Z0-9_]+)\\s*\\}\\s*$");
+
+    private final String expression;
+
+
+    /**
+     * Creates new VariableNameExtractor
+     * @param expression expression to be parsed
+     */
+    public VariableNameExtractor(String expression) {
+        this.expression = expression;
+    }
+
+    /**
+     * Extracts variable name from expression given in constructor
+     * @return Optional of variable name, empty if expression wasn't single variable
+     */
+    public Optional<String> extract() {
+        Matcher matcher = VARIABLE_NAME_PATTERN.matcher(expression);
+        if (!matcher.matches()) {
+            return Optional.empty();
+        }
+        return Optional.of(matcher.group(1));
+    }
+
+}
diff --git a/bpmn/MSOCoreBPMN/src/test/java/org/openecomp/mso/bpmn/core/internal/VariableNameExtractorTest.java b/bpmn/MSOCoreBPMN/src/test/java/org/openecomp/mso/bpmn/core/internal/VariableNameExtractorTest.java
new file mode 100644
index 0000000000..57f479f7cb
--- /dev/null
+++ b/bpmn/MSOCoreBPMN/src/test/java/org/openecomp/mso/bpmn/core/internal/VariableNameExtractorTest.java
@@ -0,0 +1,86 @@
+/*-
+ * ============LICENSE_START=======================================================
+ * ONAP - SO
+ * ================================================================================
+ * Copyright (C) 2017 AT&T Intellectual Property. All rights reserved.
+ * ================================================================================
+ * Licensed 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.
+ * ============LICENSE_END=========================================================
+ */
+
+package org.openecomp.mso.bpmn.core.internal;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import java.util.Optional;
+import org.junit.Test;
+
+public class VariableNameExtractorTest {
+
+    @Test
+    public void shouldExtractVariableName() throws Exception {
+        // given
+        String name = "A_different_NAME123";
+        String variable = "${A_different_NAME123}";
+        VariableNameExtractor extractor = new VariableNameExtractor(variable);
+        // when
+        Optional<String> extracted = extractor.extract();
+        // then
+        assertThat(extracted).isPresent().contains(name);
+    }
+
+    @Test
+    public void shouldExtractVariableNameFromWhitespaces() throws Exception {
+        // given
+        String name = "name";
+        String variable = " \n\t$ \n\t{ \n\tname \n\t} \n\t";
+        VariableNameExtractor extractor = new VariableNameExtractor(variable);
+        // when
+        Optional<String> extracted = extractor.extract();
+        // then
+        assertThat(extracted).isPresent().contains(name);
+    }
+
+    @Test
+    public void shouldReturnEmptyIfThereIsMoreThanVariable() throws Exception {
+        // given
+        String variable = "a ${test}";
+        VariableNameExtractor extractor = new VariableNameExtractor(variable);
+        // when
+        Optional<String> extracted = extractor.extract();
+        // then
+        assertThat(extracted).isNotPresent();
+    }
+
+    @Test
+    public void shouldReturnEmptyIfVariableNameIsIncorrect() throws Exception {
+        // given
+        String variable = "${name with space}";
+        VariableNameExtractor extractor = new VariableNameExtractor(variable);
+        // when
+        Optional<String> extracted = extractor.extract();
+        // then
+        assertThat(extracted).isNotPresent();
+    }
+
+    @Test
+    public void shouldReturnEmptyIfTwoVariablesPresent() throws Exception {
+        // given
+        String variable = "${var1} ${var2}";
+        VariableNameExtractor extractor = new VariableNameExtractor(variable);
+        // when
+        Optional<String> extracted = extractor.extract();
+        // then
+        assertThat(extracted).isNotPresent();
+    }
+}
\ No newline at end of file