根据Activiti的processInstanceId得到流程图，高亮当前执行中的流程。 与官方提供的不同，该类仅仅是在原图的基础上添加高亮。这样可以不需要考虑汉字乱码的问题。

ProcessDefinitionGeneratorEx.java

package com.winse.activiti.util;

import java.awt.BasicStroke;
import java.awt.Color;
import java.awt.Graphics2D;
import java.awt.Paint;
import java.awt.Stroke;
import java.awt.geom.RoundRectangle2D;
import java.awt.image.BufferedImage;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.util.List;

import javax.imageio.ImageIO;

import org.activiti.engine.RepositoryService;
import org.activiti.engine.RuntimeService;
import org.activiti.engine.impl.RepositoryServiceImpl;
import org.activiti.engine.impl.persistence.entity.ProcessDefinitionEntity;
import org.activiti.engine.impl.pvm.process.ActivityImpl;
import org.activiti.engine.runtime.ProcessInstance;
import org.apache.commons.io.FilenameUtils;


/**
 * @see org.activiti.engine.impl.bpmn.diagram.ProcessDiagramGenerator
 * @see org.activiti.engine.impl.bpmn.diagram.ProcessDiagramCanvas
 * 
 * @author winse
 */
public class ProcessDefinitionGeneratorEx {
  
  private RepositoryService repositoryService;
  private RuntimeService runtimeService;

	public ProcessDefinitionGeneratorEx() {
	}

	public ProcessDefinitionGeneratorEx(RepositoryService repositoryService, RuntimeService runtimeService) {
		this.repositoryService = repositoryService;
		this.runtimeService = runtimeService;
	}

	public RepositoryService getRepositoryService() {
		return repositoryService;
	}

	public RuntimeService getRuntimeService() {
		return runtimeService;
	}

	private static Color HIGHLIGHT_COLOR = Color.RED;
	private static Stroke THICK_TASK_BORDER_STROKE = new BasicStroke(3.0f);

	public InputStream generateDiagramWithHighLight(String processInstanceId) throws IOException {
		ProcessInstance processInstance = runtimeService.createProcessInstanceQuery()
				.processInstanceId(processInstanceId).singleResult();
		String processDefinitionId = processInstance.getProcessDefinitionId();

		ProcessDefinitionEntity definition = (ProcessDefinitionEntity) ((RepositoryServiceImpl) repositoryService)
				.getDeployedProcessDefinition(processDefinitionId);
		String diagramResourceName = definition.getDiagramResourceName();
		String deploymentId = definition.getDeploymentId();
		InputStream originDiagram = repositoryService.getResourceAsStream(deploymentId, diagramResourceName);
		BufferedImage image = ImageIO.read(originDiagram);

		List<String> activeActivityIds = ActivityUtil.getActiveActivityIds(runtimeService, processInstanceId);
		List<ActivityImpl> definitionActivities = ActivityUtil.getFlatAllActivities(definition);
		for (ActivityImpl activity : definitionActivities) {
			if (activeActivityIds.contains(activity.getId())) {
				decorate(image, //
						activity.getX(), activity.getY(), activity.getWidth(), activity.getHeight());
			}
		}

		ByteArrayOutputStream out = new ByteArrayOutputStream();
		String formatName = getDiagramExtension(diagramResourceName);
		ImageIO.write(image, formatName, out);
		return new ByteArrayInputStream(out.toByteArray());

	}
	
	/** 
	@Test
	public void testDecorete() throws FileNotFoundException, IOException {
		String diagramResourceName = "C:/Users/Winseliu/Desktop/03.jpg";
		BufferedImage image = ImageIO.read(new FileInputStream(diagramResourceName));
		decorate(image, 100, 100, 100, 100);
		FileOutputStream out = new FileOutputStream("C:/Users/Winseliu/Desktop/03-hh.jpg");
		try {
			ImageIO.write(image, getDiagramExtension(diagramResourceName), out);
		} finally {
			IoUtil.closeSilently(out);
		}
	}
	//*/

	private static void decorate(BufferedImage image, int x, int y, int width, int height) {
		Graphics2D g = image.createGraphics();
		try {
			drawHighLight(x, y, width, height, g);
		} finally {
			g.dispose();
		}
	}

	private static String getDiagramExtension(String diagramResourceName) {
//		return diagramResourceName.substring(diagramResourceName.lastIndexOf(".") + 1);
		return FilenameUtils.getExtension(diagramResourceName);
	}

	private static void drawHighLight(int x, int y, int width, int height, Graphics2D g) {
		Paint originalPaint = g.getPaint();
		Stroke originalStroke = g.getStroke();

		g.setPaint(HIGHLIGHT_COLOR);
		g.setStroke(THICK_TASK_BORDER_STROKE);

		RoundRectangle2D rect = new RoundRectangle2D.Double(x, y, width, height, 20, 20);
		g.draw(rect);

		g.setPaint(originalPaint);
		g.setStroke(originalStroke);
	}

}

ActivityUtil.java

package com.winse.activiti.util;

import java.util.ArrayList;
import java.util.List;

import org.activiti.engine.RuntimeService;
import org.activiti.engine.impl.persistence.entity.ProcessDefinitionEntity;
import org.activiti.engine.impl.pvm.process.ActivityImpl;

/**
 * 
 * @author winse
 * 
 */
public class ActivityUtil {

  public static List<String> getActiveActivityIds(RuntimeService runtimeService, String processInstanceId) {
		// 会通过id -> parent_id -> parent_id -> ... 循环找出所有的执行中的子流程
		return runtimeService.getActiveActivityIds(processInstanceId);
	}

	public static List<ActivityImpl> getFlatAllActivities(ProcessDefinitionEntity processDefinition) {
		List<ActivityImpl> result = new ArrayList<ActivityImpl>();
		flattenActivities(result, processDefinition.getActivities());
		return result;
	}

	private static void flattenActivities(List<ActivityImpl> container, List<ActivityImpl> ancestors) {
		if (ancestors.size() > 0) {
			for (ActivityImpl activity : ancestors) {
				flattenActivities(container, activity.getActivities());
			}
			container.addAll(ancestors);
		}
	}

}