common EGIZ code-style refactoring

1 files changed, 502 insertions, 466 deletions

diff --git a/eaaf_core/src/main/java/at/gv/egiz/eaaf/core/impl/idp/process/ProcessEngineImpl.java b/eaaf_core/src/main/java/at/gv/egiz/eaaf/core/impl/idp/process/ProcessEngineImpl.java
index 53f50e1f..0c4946af 100644
--- a/eaaf_core/src/main/java/at/gv/egiz/eaaf/core/impl/idp/process/ProcessEngineImpl.java
+++ b/eaaf_core/src/main/java/at/gv/egiz/eaaf/core/impl/idp/process/ProcessEngineImpl.java
@@ -1,55 +1,39 @@
-/*******************************************************************************
- * Copyright 2017 Graz University of Technology
- * EAAF-Core Components has been developed in a cooperation between EGIZ,  
- * A-SIT Plus, A-SIT, and Graz University of Technology.
+/*
+ * Copyright 2017 Graz University of Technology EAAF-Core Components has been developed in a
+ * cooperation between EGIZ, A-SIT Plus, A-SIT, and Graz University of Technology.
  *
- * Licensed under the EUPL, Version 1.2 or - as soon they will be approved by
- * the European Commission - subsequent versions of the EUPL (the "Licence");
- * You may not use this work except in compliance with the Licence.
- * You may obtain a copy of the Licence at:
+ * Licensed under the EUPL, Version 1.2 or - as soon they will be approved by the European
+ * Commission - subsequent versions of the EUPL (the "Licence"); You may not use this work except in
+ * compliance with the Licence. You may obtain a copy of the Licence at:
  * https://joinup.ec.europa.eu/news/understanding-eupl-v12
  *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the Licence is distributed on an "AS IS" basis,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the Licence for the specific language governing permissions and
- * limitations under the Licence.
- *  
- * This product combines work with different licenses. See the "NOTICE" text
- * file for details on the various modules and licenses.
- * The "NOTICE" text file is part of the distribution. Any derivative works
- * that you distribute must include a readable copy of the "NOTICE" text file.
- *******************************************************************************/
-/*******************************************************************************
- *******************************************************************************/
-/*******************************************************************************
- *******************************************************************************/
+ * Unless required by applicable law or agreed to in writing, software distributed under the Licence
+ * is distributed on an "AS IS" basis, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
+ * or implied. See the Licence for the specific language governing permissions and limitations under
+ * the Licence.
+ *
+ * This product combines work with different licenses. See the "NOTICE" text file for details on the
+ * various modules and licenses. The "NOTICE" text file is part of the distribution. Any derivative
+ * works that you distribute must include a readable copy of the "NOTICE" text file.
+*/
+
 package at.gv.egiz.eaaf.core.impl.idp.process;
 
 import java.io.InputStream;
 import java.io.Serializable;
 import java.util.HashMap;
 import java.util.Map;
+import java.util.Map.Entry;
 import java.util.concurrent.ConcurrentHashMap;
-
-import org.apache.commons.collections4.IterableUtils;
-import org.apache.commons.collections4.Predicate;
-import org.apache.commons.lang3.StringUtils;
-import org.slf4j.Logger;
-import org.slf4j.LoggerFactory;
-import org.slf4j.MDC;
-import org.springframework.beans.factory.annotation.Autowired;
-import org.springframework.context.ApplicationContext;
-
 import at.gv.egiz.eaaf.core.api.IRequest;
 import at.gv.egiz.eaaf.core.api.data.EAAFConstants;
 import at.gv.egiz.eaaf.core.api.idp.process.ExecutionContext;
 import at.gv.egiz.eaaf.core.api.idp.process.ExpressionEvaluationContext;
 import at.gv.egiz.eaaf.core.api.idp.process.ExpressionEvaluator;
 import at.gv.egiz.eaaf.core.api.idp.process.ProcessEngine;
-import at.gv.egiz.eaaf.core.api.idp.process.ProcessInstanceStoreDAO;
+import at.gv.egiz.eaaf.core.api.idp.process.ProcessInstanceStoreDao;
 import at.gv.egiz.eaaf.core.api.idp.process.Task;
-import at.gv.egiz.eaaf.core.exceptions.EAAFException;
+import at.gv.egiz.eaaf.core.exceptions.EaafException;
 import at.gv.egiz.eaaf.core.exceptions.ProcessExecutionException;
 import at.gv.egiz.eaaf.core.impl.idp.process.dao.ProcessInstanceStore;
 import at.gv.egiz.eaaf.core.impl.idp.process.model.EndEvent;
@@ -58,439 +42,491 @@ import at.gv.egiz.eaaf.core.impl.idp.process.model.ProcessNode;
 import at.gv.egiz.eaaf.core.impl.idp.process.model.StartEvent;
 import at.gv.egiz.eaaf.core.impl.idp.process.model.TaskInfo;
 import at.gv.egiz.eaaf.core.impl.idp.process.model.Transition;
+import org.apache.commons.collections4.IterableUtils;
+import org.apache.commons.lang3.StringUtils;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+import org.slf4j.MDC;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.context.ApplicationContext;
 
 /**
- * Process engine implementation allowing starting and continuing processes as well as providing means for cleanup actions.
+ * Process engine implementation allowing starting and continuing processes as well as providing
+ * means for cleanup actions.
  */
 public class ProcessEngineImpl implements ProcessEngine {
- 
-	private final Logger log = LoggerFactory.getLogger(getClass());
-
-	@Autowired ProcessInstanceStoreDAO piStoreDao;
-	@Autowired ApplicationContext context;
-	
-	private final ProcessDefinitionParser pdp = new ProcessDefinitionParser();
-
-	private final Map<String, ProcessDefinition> processDefinitions = new ConcurrentHashMap<String, ProcessDefinition>();
-
-	private final static String MDC_CTX_PI_NAME = "processInstanceId";
-	private final static String MDC_CTX_TASK_NAME = "taskId";
-
-	private ExpressionEvaluator transitionConditionExpressionEvaluator;
-
-	@Override
-	public void registerProcessDefinition(ProcessDefinition processDefinition) {
-		log.info("Registering process definition '{}'.", processDefinition.getId());
-		processDefinitions.put(processDefinition.getId(), processDefinition);
-	}
-
-	@Override
-	public String registerProcessDefinition(InputStream processDefinitionInputStream) throws ProcessDefinitionParserException{
-		final ProcessDefinition pd = pdp.parse(processDefinitionInputStream);
-		
-		postValidationOfProcessDefintion(pd);
-		
-		registerProcessDefinition(pd);
-		return pd.getId();
-	}
-	
-	/**
-	 * Sets the process definitions.
-	 *
-	 * @param processDefinitions
-	 *            The process definitions.
-	 * @throws IllegalArgumentException
-	 *             In case the process definitions contain definitions with the same identifier.
-	 */
-	public void setProcessDefinitions(Iterable<ProcessDefinition> processDefinitions) {
-		this.processDefinitions.clear();
-		for (final ProcessDefinition pd : processDefinitions) {
-			if (this.processDefinitions.containsKey(pd.getId())) {
-				throw new IllegalArgumentException("Duplicate process definition identifier '" + pd.getId() + "'.");
-			}
-			registerProcessDefinition(pd);
-		}
-	}
-
-	/**
-	 * Sets an expression evaluator that should be used to process transition condition expressions.
-	 * @param transitionConditionExpressionEvaluator The expression evaluator.
-	 */
-	public void setTransitionConditionExpressionEvaluator(
-			ExpressionEvaluator transitionConditionExpressionEvaluator) {
-		this.transitionConditionExpressionEvaluator = transitionConditionExpressionEvaluator;
-	}
-
-
-	@Override
-	public String createProcessInstance(String processDefinitionId, ExecutionContext executionContext) throws ProcessExecutionException {
-		// look for respective process definition
-		final ProcessDefinition pd = processDefinitions.get(processDefinitionId);
-		if (pd == null) {
-			throw new ProcessExecutionException("Unable to find process definition for process '" + processDefinitionId + "'.");
-		}
-		// create and keep process instance
-		final ProcessInstance pi = new ProcessInstance(pd, executionContext);
-		log.info("Creating process instance from process definition '{}': {}", processDefinitionId, pi.getId());
-
-		try {
-			saveOrUpdateProcessInstance(pi);
-			
-		} catch (final EAAFException e) {
-			throw new ProcessExecutionException("Unable to persist process instance.", e);
-		}
-
-		return pi.getId();
-	}
-
-	@Override
-	public String createProcessInstance(String processDefinitionId) throws ProcessExecutionException {
-		return createProcessInstance(processDefinitionId, null);
-	}
-
-	@Override
-	public void start(IRequest pendingReq) throws ProcessExecutionException {
-		try {
-			if (StringUtils.isEmpty(pendingReq.getProcessInstanceId())) {
-				log.error("Pending-request with id:" + pendingReq.getPendingRequestId() 
-					+ " includes NO 'ProcessInstanceId'");
-				throw new ProcessExecutionException("Pending-request with id:" + pendingReq.getPendingRequestId() 
-					+ " includes NO 'ProcessInstanceId'");
-			}
-			
-			final ProcessInstance pi = loadProcessInstance(pendingReq.getProcessInstanceId());
-
-			if (pi == null ) {
-				throw new ProcessExecutionException("Process instance '" + pendingReq.getProcessInstanceId() + "' does not exist.");
-				
-			}
-			
-			MDC.put(MDC_CTX_PI_NAME, pi.getId());
-
-			if (!ProcessInstanceState.NOT_STARTED.equals(pi.getState())) {
-				throw new ProcessExecutionException("Process instance '" + pi.getId() + "' has already been started (current state is " + pi.getState() + ").");
-			}
-			log.info("Starting process instance '{}'.", pi.getId());
-			// execute process
-			pi.setState(ProcessInstanceState.STARTED);
-			execute(pi, pendingReq);
-
-			//store ProcessInstance if it is not already ended
-			if (!ProcessInstanceState.ENDED.equals(pi.getState()))
-				saveOrUpdateProcessInstance(pi);
-				
-		} catch (final EAAFException e) {
-			throw new ProcessExecutionException("Unable to load/save process instance.", e);
-
-		} finally {
-			MDC.remove(MDC_CTX_PI_NAME);
-		}
-	}
-	
-	@Override
-	public void signal(IRequest pendingReq) throws ProcessExecutionException {
-
-		try {
-			if (StringUtils.isEmpty(pendingReq.getProcessInstanceId())) {
-				log.error("Pending-request with id:" + pendingReq.getPendingRequestId() 
-					+ " includes NO 'ProcessInstanceId'");
-				throw new ProcessExecutionException("Pending-request with id:" + pendingReq.getPendingRequestId() 
-					+ " includes NO 'ProcessInstanceId'");
-			}
-			
-			final ProcessInstance pi = loadProcessInstance(pendingReq.getProcessInstanceId());
-
-			if (pi == null ) {
-				throw new ProcessExecutionException("Process instance '" + pendingReq.getProcessInstanceId() + "' does not exist.");
-				
-			}
-			
-			MDC.put(MDC_CTX_PI_NAME, pi.getId());
-
-			if (!ProcessInstanceState.SUSPENDED.equals(pi.getState())) {
-				throw new ProcessExecutionException("Process instance '" + pi.getId() + "' has not been suspended (current state is " + pi.getState() + ").");
-			}
-
-			log.debug("Waking up process instance '{}'.", pi.getId());
-			pi.setState(ProcessInstanceState.STARTED);
-
-			//put pending-request ID on execution-context because it could be changed
-			pi.getExecutionContext().put(EAAFConstants.PARAM_HTTP_TARGET_PENDINGREQUESTID, pendingReq.getPendingRequestId());
-			
-			execute(pi, pendingReq);
-
-			//store ProcessInstance if it is not already ended
-			if (!ProcessInstanceState.ENDED.equals(pi.getState()))
-				saveOrUpdateProcessInstance(pi);
-						
-		} catch (final EAAFException e) {
-			throw new ProcessExecutionException("Unable to load/save process instance.", e);
-
-		} finally {
-			MDC.remove(MDC_CTX_PI_NAME);
-		}
-	}
-	
-
-	/**
-	 * Instantiates a task implementation given by a {@link TaskInfo}.
-	 * @param ti The task info.
-	 * @return A Task implementation or {@code null} if the task info does not reference any task implementing classes.
-	 * @throws ProcessExecutionException Thrown in case of error (when the referenced class does not implement {@link Task} for instance).
-	 */
-	private Task createTaskInstance(TaskInfo ti) throws ProcessExecutionException {
-		final String clazz = StringUtils.trimToNull(ti.getTaskImplementingClass());
-		Task task = null;
-		
-		if (clazz != null) {
-			log.debug("Instantiating task implementing class '{}'.", clazz);
-			Object instanceClass = null;
-			try {
-				instanceClass = context.getBean(clazz);
-				
-			} catch (final Exception e) {
-				throw new ProcessExecutionException("Unable to get class '" + clazz + "' associated with task '" + ti.getId() + "' .", e);
-				
-			}
-			if (instanceClass == null || !(instanceClass instanceof Task)) {
-				throw new ProcessExecutionException("Class '" + clazz + "' associated with task '" + ti.getId() + "' is not assignable to " + Task.class.getName() + ".");
-				
-			}
-			try {
-				task = (Task) instanceClass;
-				
-			} catch (final Exception e) {
-				throw new ProcessExecutionException("Unable to instantiate class '" + clazz + "' associated with task '" + ti.getId() + "' .", e);
-			}
-		}
-
-		return task;
-	}
-
-	/**
-	 * Starts/executes a given process instance.
-	 * @param pi The process instance.
-	 * @param pendingReq 
-	 * @throws ProcessExecutionException Thrown in case of error.
-	 */
-	private void execute(final ProcessInstance pi, IRequest pendingReq) throws ProcessExecutionException {
-		if (ProcessInstanceState.ENDED.equals(pi.getState())) {
-			throw new ProcessExecutionException("Process for instance '" + pi.getId() + "' has already been ended.");
-		}
-		final ProcessDefinition pd = pi.getProcessDefinition();
-		final ProcessNode processNode = pd.getProcessNode(pi.getNextId());
-		log.debug("Processing node '{}'.", processNode.getId());
-		
-		// distinguish process node types StartEvent, TaskInfo and EndEvent
-		
-		if (processNode instanceof TaskInfo) {
-			// TaskInfo types need to be executed
-			final TaskInfo ti = (TaskInfo) processNode;
-			MDC.put(MDC_CTX_TASK_NAME, ti.getId());
-			try {
-				log.debug("Processing task '{}'.", ti.getId());
-				final Task task = createTaskInstance(ti);
-				if (task != null) {
-					try {
-						log.debug("Executing task implementation for task '{}'.", ti.getId());
-						log.trace("Execution context before task execution: {}", pi.getExecutionContext().keySet());
-						pendingReq = task.execute(pendingReq, pi.getExecutionContext());
-						log.debug("Returned from execution of task '{}'.", ti.getId());
-						log.trace("Execution context after task execution: {}", pi.getExecutionContext().keySet());
-												
-					} catch (final Throwable t) {
-						throw new ProcessExecutionException("Error executing task '" + ti.getId() + "'.", t);
-						
-					}
-					
-					//check if process was cancelled dynamically by task
-					if (pi.getExecutionContext().isProcessCancelled()) {
-						log.debug("Processing task '{}' was cancelled by Task: '{}'.", pi.getId(), ti.getId());
-						processFinishEvent(pi);
-						return;
-						
-					}
-					
-				} else {
-					log.debug("No task implementing class set.");
-					
-				}
-			} finally {
-				MDC.remove(MDC_CTX_TASK_NAME);
-				
-			}
-			
-		} else if (processNode instanceof EndEvent) {
-			processFinishEvent(pi);
-			return;
-			
-		}
-		
-		final ExpressionEvaluationContext expressionContext = new ExpressionEvaluationContextImpl(pi);
-		
-		// traverse pointer
-		final Transition t = IterableUtils.find(processNode.getOutgoingTransitions(), new Predicate<Transition>() {
-			@Override
-			public boolean evaluate(Transition transition) {
-				if (transitionConditionExpressionEvaluator != null && transition.getConditionExpression() != null) {
-					log.trace("Evaluating transition expression '{}'.", transition.getConditionExpression());
-					return transitionConditionExpressionEvaluator.evaluate(expressionContext, transition.getConditionExpression());
-				}
-				return true;
-			}
-		});
-		if (t == null) {
-			throw new ProcessExecutionException("No valid transition starting from process node '" + processNode.getId()+ "'.");
-		}
-		log.trace("Found suitable transition: {}", t);
-		// update pointer
-		log.trace("Shifting process token from '{}' to '{}'.", pi.getNextId(), t.getTo().getId());
-		pi.setNextId(t.getTo().getId());
-		
-		// inspect current task
-		if (t.getTo() instanceof TaskInfo && (((TaskInfo) t.getTo()).isAsync())) {
-			// immediately return in case of asynchonous task
-			log.debug("Suspending process instance '{}' for asynchronous task '{}'.", pi.getId(), t.getTo().getId());
-			pi.setState(ProcessInstanceState.SUSPENDED);
-			return;
-		}
-		
-		// continue execution in case of StartEvent or Task
-		if (processNode instanceof StartEvent || processNode instanceof TaskInfo) {
-			execute(pi, pendingReq);
-		}
-	}
-	
-	@Override
-	public ProcessInstance getProcessInstance(String processInstanceId) {
-
-		ProcessInstance processInstance;
-		try {
-			processInstance = loadProcessInstance(processInstanceId);
-
-		} catch (final EAAFException e) {
-			throw new RuntimeException("The process instance '" + processInstanceId + "' could not be retrieved.", e);
-		}
-
-		if (processInstance == null) {
-			throw new IllegalArgumentException("The process instance '" + processInstanceId + "' does not/no longer exist.");
-		}
-
-		return processInstance;
-	}
-
-	/**
-	 * Persists a {@link ProcessInstance} to the database.
-	 * @param processInstance The object to persist.
-	 * @throws MOADatabaseException Thrown if an error occurs while accessing the database.
-	 */
-	private void saveOrUpdateProcessInstance(ProcessInstance processInstance) throws EAAFException {
-		final ProcessInstanceStore store = new ProcessInstanceStore();
-
-		final ExecutionContext ctx = processInstance.getExecutionContext();
-
-		final Map<String, Serializable> ctxData = new HashMap<String, Serializable>();
-		for (final String key : ctx.keySet()) {
-			ctxData.put(key, ctx.get(key));
-		}
-		store.setExecutionContextData(ctxData);
-
-		store.setNextTaskId(processInstance.getNextId());
-		store.setProcessDefinitionId(processInstance.getProcessDefinition().getId());
-
-		store.setProcessInstanceId(processInstance.getId());
-		store.setProcessState(processInstance.getState());
-
-		piStoreDao.saveOrUpdate(store);
-	}
-
-	/**
-	 * Load a {@link ProcessInstance} with a certain id from the database.
-	 * @param processInstanceId The process instance id
-	 * @return The process instance corresponding to the id or {@code null} if no such object is found.
-	 * @throws MOADatabaseException Thrown if an error occurs while accessing the database.
-	 */
-	private ProcessInstance loadProcessInstance(String processInstanceId) throws EAAFException {
-
-		final ProcessInstanceStore piStore = piStoreDao.load(processInstanceId);
-
-		if (piStore == null) {
-			return null;
-		}
-
-		final ExecutionContext executionContext = new ExecutionContextImpl(piStore.getProcessInstanceId());
-
-		final Map<String, Serializable> executionContextData = piStore.getExecutionContextData();
-		for (final String key : executionContextData.keySet()) {
-			executionContext.put(key, executionContextData.get(key));
-		}
-
-		final ProcessInstance pi = new ProcessInstance(processDefinitions.get(piStore.getProcessDefinitionId()), executionContext);
-		pi.setNextId(piStore.getNextTaskId());
-		pi.setState(piStore.getProcessState());
-
-		return pi;
-	}
-
-	/* (non-Javadoc)
-	 * @see at.gv.egovernment.moa.id.process.ProcessEngine#deleteProcessInstance(java.lang.String)
-	 */
-	@Override
-	public void deleteProcessInstance(String processInstanceId) throws ProcessExecutionException {
-		if (StringUtils.isEmpty(processInstanceId)) {
-			throw new ProcessExecutionException("Unable to remove process instance: ProcessInstanceId is empty");
-			
-		}
-			
-		try {
-			piStoreDao.remove(processInstanceId);
-			
-		} catch (final EAAFException e) {
-			throw new ProcessExecutionException("Unable to remove process instance.", e);
-			
-		}
-		
-	}
-	
-	/**
-	 * Finish a process-flow and remove any process-flow related information
-	 * 
-	 * @param pi
-	 * @throws ProcessExecutionException
-	 */
-	private void processFinishEvent(ProcessInstance pi) throws ProcessExecutionException {
-		log.info("Finishing process instance '{}'.", pi.getId());
-
-		try {
-			piStoreDao.remove(pi.getId());
-			
-		} catch (final EAAFException e) {
-			throw new ProcessExecutionException("Unable to remove process instance.", e);
-			
-		}
-		pi.setState(ProcessInstanceState.ENDED);
-		log.debug("Final process context: {}", pi.getExecutionContext().keySet());
-		
-	}
-	
-	/**
-	 * Perform some post-validation operations on process definition 
-	 * 
-	 * Like: check if all tasks that are defined are available on context
-	 * 
-	 * @param pd
-	 * @throws ProcessDefinitionParserException
-	 */
-	private void postValidationOfProcessDefintion(ProcessDefinition pd) throws ProcessDefinitionParserException{
-		try {
-			for(final TaskInfo task : pd.getTaskInfos().values()) {
-				createTaskInstance(task);		
-			}
-			
-		} catch (final ProcessExecutionException e) {
-			log.error("Post-validation of process definition: {} find an error: {}", pd.getId(), e.getMessage());
-			throw new ProcessDefinitionParserException("Post-validation find an error in process definition:" + pd.getId(), e);
-			
-		}
-	}
+
+  private final Logger log = LoggerFactory.getLogger(getClass());
+
+  @Autowired
+  ProcessInstanceStoreDao piStoreDao;
+  @Autowired
+  ApplicationContext context;
+
+  private final ProcessDefinitionParser pdp = new ProcessDefinitionParser();
+
+  private final Map<String, ProcessDefinition> processDefinitions = new ConcurrentHashMap<>();
+
+  private static final String MDC_CTX_PI_NAME = "processInstanceId";
+  private static final String MDC_CTX_TASK_NAME = "taskId";
+
+  private ExpressionEvaluator transitionConditionExpressionEvaluator;
+
+  @Override
+  public void registerProcessDefinition(final ProcessDefinition processDefinition) {
+    log.info("Registering process definition '{}'.", processDefinition.getId());
+    processDefinitions.put(processDefinition.getId(), processDefinition);
+  }
+
+  @Override
+  public String registerProcessDefinition(final InputStream processDefinitionInputStream)
+      throws ProcessDefinitionParserException {
+    final ProcessDefinition pd = pdp.parse(processDefinitionInputStream);
+
+    postValidationOfProcessDefintion(pd);
+
+    registerProcessDefinition(pd);
+    return pd.getId();
+  }
+
+  /**
+   * Sets the process definitions.
+   *
+   * @param processDefinitions The process definitions.
+   * @throws IllegalArgumentException In case the process definitions contain definitions with the
+   *         same identifier.
+   */
+  public void setProcessDefinitions(final Iterable<ProcessDefinition> processDefinitions) {
+    this.processDefinitions.clear();
+    for (final ProcessDefinition pd : processDefinitions) {
+      if (this.processDefinitions.containsKey(pd.getId())) {
+        throw new IllegalArgumentException(
+            "Duplicate process definition identifier '" + pd.getId() + "'.");
+      }
+      registerProcessDefinition(pd);
+    }
+  }
+
+  /**
+   * Sets an expression evaluator that should be used to process transition condition expressions.
+   *
+   * @param transitionConditionExpressionEvaluator The expression evaluator.
+   */
+  public void setTransitionConditionExpressionEvaluator(
+      final ExpressionEvaluator transitionConditionExpressionEvaluator) {
+    this.transitionConditionExpressionEvaluator = transitionConditionExpressionEvaluator;
+  }
+
+
+  @Override
+  public String createProcessInstance(final String processDefinitionId,
+      final ExecutionContext executionContext) throws ProcessExecutionException {
+    // look for respective process definition
+    final ProcessDefinition pd = processDefinitions.get(processDefinitionId);
+    if (pd == null) {
+      throw new ProcessExecutionException(
+          "Unable to find process definition for process '" + processDefinitionId + "'.");
+    }
+    // create and keep process instance
+    final ProcessInstance pi = new ProcessInstance(pd, executionContext);
+    log.info("Creating process instance from process definition '{}': {}", processDefinitionId,
+        pi.getId());
+
+    try {
+      saveOrUpdateProcessInstance(pi);
+
+    } catch (final EaafException e) {
+      throw new ProcessExecutionException("Unable to persist process instance.", e);
+    }
+
+    return pi.getId();
+  }
+
+  @Override
+  public String createProcessInstance(final String processDefinitionId)
+      throws ProcessExecutionException {
+    return createProcessInstance(processDefinitionId, null);
+  }
+
+  @Override
+  public void start(final IRequest pendingReq) throws ProcessExecutionException {
+    try {
+      if (StringUtils.isEmpty(pendingReq.getProcessInstanceId())) {
+        log.error("Pending-request with id:" + pendingReq.getPendingRequestId()
+            + " includes NO 'ProcessInstanceId'");
+        throw new ProcessExecutionException("Pending-request with id:"
+            + pendingReq.getPendingRequestId() + " includes NO 'ProcessInstanceId'");
+      }
+
+      final ProcessInstance pi = loadProcessInstance(pendingReq.getProcessInstanceId());
+
+      if (pi == null) {
+        throw new ProcessExecutionException(
+            "Process instance '" + pendingReq.getProcessInstanceId() + "' does not exist.");
+
+      }
+
+      MDC.put(MDC_CTX_PI_NAME, pi.getId());
+
+      if (!ProcessInstanceState.NOT_STARTED.equals(pi.getState())) {
+        throw new ProcessExecutionException("Process instance '" + pi.getId()
+            + "' has already been started (current state is " + pi.getState() + ").");
+      }
+      log.info("Starting process instance '{}'.", pi.getId());
+      // execute process
+      pi.setState(ProcessInstanceState.STARTED);
+      execute(pi, pendingReq);
+
+      // store ProcessInstance if it is not already ended
+      if (!ProcessInstanceState.ENDED.equals(pi.getState())) {
+        saveOrUpdateProcessInstance(pi);
+      }
+
+    } catch (final EaafException e) {
+      throw new ProcessExecutionException("Unable to load/save process instance.", e);
+
+    } finally {
+      MDC.remove(MDC_CTX_PI_NAME);
+    }
+  }
+
+  @Override
+  public void signal(final IRequest pendingReq) throws ProcessExecutionException {
+
+    try {
+      if (StringUtils.isEmpty(pendingReq.getProcessInstanceId())) {
+        log.error("Pending-request with id:" + pendingReq.getPendingRequestId()
+            + " includes NO 'ProcessInstanceId'");
+        throw new ProcessExecutionException("Pending-request with id:"
+            + pendingReq.getPendingRequestId() + " includes NO 'ProcessInstanceId'");
+      }
+
+      final ProcessInstance pi = loadProcessInstance(pendingReq.getProcessInstanceId());
+
+      if (pi == null) {
+        throw new ProcessExecutionException(
+            "Process instance '" + pendingReq.getProcessInstanceId() + "' does not exist.");
+
+      }
+
+      MDC.put(MDC_CTX_PI_NAME, pi.getId());
+
+      if (!ProcessInstanceState.SUSPENDED.equals(pi.getState())) {
+        throw new ProcessExecutionException("Process instance '" + pi.getId()
+            + "' has not been suspended (current state is " + pi.getState() + ").");
+      }
+
+      log.debug("Waking up process instance '{}'.", pi.getId());
+      pi.setState(ProcessInstanceState.STARTED);
+
+      // put pending-request ID on execution-context because it could be changed
+      pi.getExecutionContext().put(EAAFConstants.PARAM_HTTP_TARGET_PENDINGREQUESTID,
+          pendingReq.getPendingRequestId());
+
+      execute(pi, pendingReq);
+
+      // store ProcessInstance if it is not already ended
+      if (!ProcessInstanceState.ENDED.equals(pi.getState())) {
+        saveOrUpdateProcessInstance(pi);
+      }
+
+    } catch (final EaafException e) {
+      throw new ProcessExecutionException("Unable to load/save process instance.", e);
+
+    } finally {
+      MDC.remove(MDC_CTX_PI_NAME);
+    }
+  }
+
+
+  /**
+   * Instantiates a task implementation given by a {@link TaskInfo}.
+   *
+   * @param ti The task info.
+   * @return A Task implementation or {@code null} if the task info does not reference any task
+   *         implementing classes.
+   * @throws ProcessExecutionException Thrown in case of error (when the referenced class does not
+   *         implement {@link Task} for instance).
+   */
+  private Task createTaskInstance(final TaskInfo ti) throws ProcessExecutionException {
+    final String clazz = StringUtils.trimToNull(ti.getTaskImplementingClass());
+    Task task = null;
+
+    if (clazz != null) {
+      log.debug("Instantiating task implementing class '{}'.", clazz);
+      Object instanceClass = null;
+      try {
+        instanceClass = context.getBean(clazz);
+
+      } catch (final Exception e) {
+        throw new ProcessExecutionException(
+            "Unable to get class '" + clazz + "' associated with task '" + ti.getId() + "' .", e);
+
+      }
+      if (instanceClass == null || !(instanceClass instanceof Task)) {
+        throw new ProcessExecutionException("Class '" + clazz + "' associated with task '"
+            + ti.getId() + "' is not assignable to " + Task.class.getName() + ".");
+
+      }
+      try {
+        task = (Task) instanceClass;
+
+      } catch (final Exception e) {
+        throw new ProcessExecutionException("Unable to instantiate class '" + clazz
+            + "' associated with task '" + ti.getId() + "' .", e);
+      }
+    }
+
+    return task;
+  }
+
+  /**
+   * Starts/executes a given process instance.
+   *
+   * @param pi The process instance.
+   * @param pendingReq current pending request
+   * @throws ProcessExecutionException Thrown in case of error.
+   */
+  private void execute(final ProcessInstance pi, IRequest pendingReq)
+      throws ProcessExecutionException {
+    if (ProcessInstanceState.ENDED.equals(pi.getState())) {
+      throw new ProcessExecutionException(
+          "Process for instance '" + pi.getId() + "' has already been ended.");
+    }
+    final ProcessDefinition pd = pi.getProcessDefinition();
+    final ProcessNode processNode = pd.getProcessNode(pi.getNextId());
+    log.debug("Processing node '{}'.", processNode.getId());
+
+    // distinguish process node types StartEvent, TaskInfo and EndEvent
+
+    if (processNode instanceof TaskInfo) {
+      // TaskInfo types need to be executed
+      final TaskInfo ti = (TaskInfo) processNode;
+      MDC.put(MDC_CTX_TASK_NAME, ti.getId());
+      try {
+        log.debug("Processing task '{}'.", ti.getId());
+        final Task task = createTaskInstance(ti);
+        if (task != null) {
+          try {
+            log.debug("Executing task implementation for task '{}'.", ti.getId());
+            log.trace("Execution context before task execution: {}",
+                pi.getExecutionContext().keySet());
+            pendingReq = task.execute(pendingReq, pi.getExecutionContext());
+            log.debug("Returned from execution of task '{}'.", ti.getId());
+            log.trace("Execution context after task execution: {}",
+                pi.getExecutionContext().keySet());
+
+          } catch (final Throwable t) {
+            throw new ProcessExecutionException("Error executing task '" + ti.getId() + "'.", t);
+
+          }
+
+          // check if process was cancelled dynamically by task
+          if (pi.getExecutionContext().isProcessCancelled()) {
+            log.debug("Processing task '{}' was cancelled by Task: '{}'.", pi.getId(), ti.getId());
+            processFinishEvent(pi);
+            return;
+
+          }
+
+        } else {
+          log.debug("No task implementing class set.");
+
+        }
+      } finally {
+        MDC.remove(MDC_CTX_TASK_NAME);
+
+      }
+
+    } else if (processNode instanceof EndEvent) {
+      processFinishEvent(pi);
+      return;
+
+    }
+
+    final ExpressionEvaluationContext expressionContext = new ExpressionEvaluationContextImpl(pi);
+
+    // traverse pointer
+    final Transition t = IterableUtils.find(processNode.getOutgoingTransitions(), transition -> {
+      if (transitionConditionExpressionEvaluator != null
+          && transition.getConditionExpression() != null) {
+        log.trace("Evaluating transition expression '{}'.", transition.getConditionExpression());
+        return transitionConditionExpressionEvaluator.evaluate(expressionContext,
+            transition.getConditionExpression());
+      }
+      return true;
+    });
+    if (t == null) {
+      throw new ProcessExecutionException(
+          "No valid transition starting from process node '" + processNode.getId() + "'.");
+    }
+    log.trace("Found suitable transition: {}", t);
+    // update pointer
+    log.trace("Shifting process token from '{}' to '{}'.", pi.getNextId(), t.getTo().getId());
+    pi.setNextId(t.getTo().getId());
+
+    // inspect current task
+    if (t.getTo() instanceof TaskInfo && (((TaskInfo) t.getTo()).isAsync())) {
+      // immediately return in case of asynchonous task
+      log.debug("Suspending process instance '{}' for asynchronous task '{}'.", pi.getId(),
+          t.getTo().getId());
+      pi.setState(ProcessInstanceState.SUSPENDED);
+      return;
+    }
+
+    // continue execution in case of StartEvent or Task
+    if (processNode instanceof StartEvent || processNode instanceof TaskInfo) {
+      execute(pi, pendingReq);
+    }
+  }
+
+  @Override
+  public ProcessInstance getProcessInstance(final String processInstanceId) {
+
+    ProcessInstance processInstance;
+    try {
+      processInstance = loadProcessInstance(processInstanceId);
+
+    } catch (final EaafException e) {
+      throw new RuntimeException(
+          "The process instance '" + processInstanceId + "' could not be retrieved.", e);
+    }
+
+    if (processInstance == null) {
+      throw new IllegalArgumentException(
+          "The process instance '" + processInstanceId + "' does not/no longer exist.");
+    }
+
+    return processInstance;
+  }
+
+  /**
+   * Persists a {@link ProcessInstance} to the database.
+   *
+   * @param processInstance The object to persist.
+   * @throws MOADatabaseException Thrown if an error occurs while accessing the database.
+   */
+  private void saveOrUpdateProcessInstance(final ProcessInstance processInstance)
+      throws EaafException {
+    final ProcessInstanceStore store = new ProcessInstanceStore();
+
+    final ExecutionContext ctx = processInstance.getExecutionContext();
+
+    final Map<String, Serializable> ctxData = new HashMap<>();
+    for (final String key : ctx.keySet()) {
+      ctxData.put(key, ctx.get(key));
+    }
+    store.setExecutionContextData(ctxData);
+
+    store.setNextTaskId(processInstance.getNextId());
+    store.setProcessDefinitionId(processInstance.getProcessDefinition().getId());
+
+    store.setProcessInstanceId(processInstance.getId());
+    store.setProcessState(processInstance.getState());
+
+    piStoreDao.saveOrUpdate(store);
+  }
+
+  /**
+   * Load a {@link ProcessInstance} with a certain id from the database.
+   *
+   * @param processInstanceId The process instance id
+   * @return The process instance corresponding to the id or {@code null} if no such object is
+   *         found.
+   * @throws MOADatabaseException Thrown if an error occurs while accessing the database.
+   */
+  private ProcessInstance loadProcessInstance(final String processInstanceId) throws EaafException {
+
+    final ProcessInstanceStore piStore = piStoreDao.load(processInstanceId);
+
+    if (piStore == null) {
+      return null;
+    }
+
+    final ExecutionContext executionContext =
+        new ExecutionContextImpl(piStore.getProcessInstanceId());
+
+    final Map<String, Serializable> executionContextData = piStore.getExecutionContextData();
+    for (final Entry<String, Serializable> el : executionContextData.entrySet()) {
+      executionContext.put(el.getKey(), el.getValue());
+    }
+
+    final ProcessInstance pi = new ProcessInstance(
+        processDefinitions.get(piStore.getProcessDefinitionId()), executionContext);
+    pi.setNextId(piStore.getNextTaskId());
+    pi.setState(piStore.getProcessState());
+
+    return pi;
+  }
+
+  /*
+   * (non-Javadoc)
+   *
+   * @see at.gv.egovernment.moa.id.process.ProcessEngine#deleteProcessInstance(java.lang.String)
+   */
+  @Override
+  public void deleteProcessInstance(final String processInstanceId)
+      throws ProcessExecutionException {
+    if (StringUtils.isEmpty(processInstanceId)) {
+      throw new ProcessExecutionException(
+          "Unable to remove process instance: ProcessInstanceId is empty");
+
+    }
+
+    try {
+      piStoreDao.remove(processInstanceId);
+
+    } catch (final EaafException e) {
+      throw new ProcessExecutionException("Unable to remove process instance.", e);
+
+    }
+
+  }
+
+  /**
+   * Finish a process-flow and remove any process-flow related information.
+   *
+   * @param pi current process instance
+   * @throws ProcessExecutionException In case of an process error
+   */
+  private void processFinishEvent(final ProcessInstance pi) throws ProcessExecutionException {
+    log.info("Finishing process instance '{}'.", pi.getId());
+
+    try {
+      piStoreDao.remove(pi.getId());
+
+    } catch (final EaafException e) {
+      throw new ProcessExecutionException("Unable to remove process instance.", e);
+
+    }
+    pi.setState(ProcessInstanceState.ENDED);
+    log.debug("Final process context: {}", pi.getExecutionContext().keySet());
+
+  }
+
+  /**
+   * Perform some post-validation operations on process definition.
+   *
+   * <p>
+   * Like: check if all tasks that are defined are available on context
+   * </p>
+   *
+   * @param pd current process definition
+   * @throws ProcessDefinitionParserException In case of a parser error
+   */
+  private void postValidationOfProcessDefintion(final ProcessDefinition pd)
+      throws ProcessDefinitionParserException {
+    try {
+      for (final TaskInfo task : pd.getTaskInfos().values()) {
+        createTaskInstance(task);
+      }
+
+    } catch (final ProcessExecutionException e) {
+      log.error("Post-validation of process definition: {} find an error: {}", pd.getId(),
+          e.getMessage());
+      throw new ProcessDefinitionParserException(
+          "Post-validation find an error in process definition:" + pd.getId(), e);
+
+    }
+  }
 }