获取流程实例

流程实例获取的源码解析

以获取默认的流程实例为例，来解释整个流程实例的获取过程

文件位置：/org/activiti/engine/ProcessEngines.java

第一步：通过getDefaultProcessEngine来获取，可以看出其调用的当前类的getProcessEngine方法。

//获取默认的流程引擎实例  NAME_DEFAULT="default"
  public static ProcessEngine getDefaultProcessEngine() {
    return getProcessEngine(NAME_DEFAULT);
  }

第二步: 根据ProcessEngine的name获取指定的ProcessEngine

  /**
   * @author 郑小康
   * 根据ProcessEngine的name获取指定的ProcessEngine
   * */
  public static ProcessEngine getProcessEngine(String processEngineName) {
    if (!isInitialized()) {
      init();
    }
    return processEngines.get(processEngineName);
  }

第三步：调用init方法，来对流程引擎进行初始化

/**
   * @author 郑小康
   *
   * 该方法使用了synchronized 再次检测其是否被初始化，避免其它客户端进行了初始化
   *
   * 1.检验是否初始化,默认值为false,第一次进来肯定是false,然后向下进行执行
   *
   * 2.检验processEngines是否存在,如果不存在则构建一个HashMap实例
   *
   * 3.获取当前类加载器，根据类加载器获取activiti.cfg.xml资源文件，如果不存在则扔出异常，要求必须命名为activiti.cfg.xml
   *
   * 4.遍历所有的资源文件,通过initProcessEngineFromSpringResource这个方法构建其processEngine实例并添加其对应的属性
   *
   * 5.将初始化属性isInitialized的值设为true
   * */
  public synchronized static void init() {
    if (!isInitialized()) {
      if (processEngines == null) {
        processEngines = new HashMap<String, ProcessEngine>();
      }
      ClassLoader classLoader = ReflectUtil.getClassLoader();
      Enumeration<URL> resources = null;
      try {
        resources = classLoader.getResources("activiti.cfg.xml");
      } catch (IOException e) {
        throw new ActivitiIllegalArgumentException("problem retrieving activiti.cfg.xml resources on the classpath: " + System.getProperty("java.class.path"), e);
      }

      Set<URL> configUrls = new HashSet<URL>();
      while (resources.hasMoreElements()) {
        configUrls.add(resources.nextElement());
      }
      for (Iterator<URL> iterator = configUrls.iterator(); iterator.hasNext();) {
        URL resource = iterator.next();
        log.info("Initializing process engine using configuration '{}'", resource.toString());
        initProcessEngineFromResource(resource);
      }

      try {
        resources = classLoader.getResources("activiti-context.xml");
      } catch (IOException e) {
        throw new ActivitiIllegalArgumentException("problem retrieving activiti-context.xml resources on the classpath: " + System.getProperty("java.class.path"), e);
      }
      while (resources.hasMoreElements()) {
        URL resource = resources.nextElement();
        log.info("Initializing process engine using Spring configuration '{}'", resource.toString());
        initProcessEngineFromSpringResource(resource);
      }

      setInitialized(true);
    } else {
      log.info("Process engines already initialized");
    }
  }

第四步：通过initProcessEngineFromResource方法来进行ProcessEngine实例以及其一系列相关属性的创建,核心是调用了buildProcessEngine来构建其实例

 /**
   * @author 郑小康
   *
   * 1.从processEngineInfosByResourceUrl中获取流程配置信息
   *
   * 2.如果processEngineInfo不为空，移除所有与ProcessEngine相关的信息
   *
   * 3.构建ProcessEngine实例，将其添加到processEngines
   *
   * 4.构建processEngineInfo实例，将其加入到processEngineInfosByName processEngineInfosByResourceUrl  processEngineInfos.add(processEngineInfo);
   *
   * */
  private static ProcessEngineInfo initProcessEngineFromResource(URL resourceUrl) {
    ProcessEngineInfo processEngineInfo = processEngineInfosByResourceUrl.get(resourceUrl.toString());
    // if there is an existing process engine info
    if (processEngineInfo != null) {
      // remove that process engine from the member fields
      processEngineInfos.remove(processEngineInfo);
      if (processEngineInfo.getException() == null) {
        String processEngineName = processEngineInfo.getName();
        processEngines.remove(processEngineName);
        processEngineInfosByName.remove(processEngineName);
      }
      processEngineInfosByResourceUrl.remove(processEngineInfo.getResourceUrl());
    }

    String resourceUrlString = resourceUrl.toString();
    try {
      log.info("initializing process engine for resource {}", resourceUrl);
      ProcessEngine processEngine = buildProcessEngine(resourceUrl);
      String processEngineName = processEngine.getName();
      log.info("initialised process engine {}", processEngineName);
      processEngineInfo = new ProcessEngineInfoImpl(processEngineName, resourceUrlString, null);
      processEngines.put(processEngineName, processEngine);
      processEngineInfosByName.put(processEngineName, processEngineInfo);
    } catch (Throwable e) {
      log.error("Exception while initializing process engine: {}", e.getMessage(), e);
      processEngineInfo = new ProcessEngineInfoImpl(null, resourceUrlString, getExceptionString(e));
    }
    processEngineInfosByResourceUrl.put(resourceUrlString, processEngineInfo);
    processEngineInfos.add(processEngineInfo);
    return processEngineInfo;
  }

第五步：buildProcessEngine方法来构建实例，先获取配置实例，在调用其的buildProcessEngine方法来实例化，具体实现类是ProcessEngineConfigurationImpl

 /**
   * @author 郑小康
   * 根据文件路径，构建其ProcessEngineConfiguration实例,调用buildProcessEngine方法创建ProcessEngine实例
   * */
  private static ProcessEngine buildProcessEngine(URL resource) {
    InputStream inputStream = null;
    try {
      inputStream = resource.openStream();
      ProcessEngineConfiguration processEngineConfiguration = ProcessEngineConfiguration.createProcessEngineConfigurationFromInputStream(inputStream);
      return processEngineConfiguration.buildProcessEngine();

    } catch (IOException e) {
      throw new ActivitiIllegalArgumentException("couldn't open resource stream: " + e.getMessage(), e);
    } finally {
      IoUtil.closeSilently(inputStream);
    }
  }

以上就是一个流程实例获取的过程，其实不难发现，我们不一定要获取默认的，我们也可以根据指定的processEngineName利用getProcessEngine来获取对应的流程实例，结合上文我们还能自己构建流程配置实例，直接进行获取

配置文件

<beans xmlns="http://www.springframework.org/schema/beans"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://www.springframework.org/schema/beans   
       http://www.springframework.org/schema/beans/spring-beans.xsd">

	<bean id="dataSource" class="com.alibaba.druid.pool.DruidDataSource">
		<property name="driverClassName">
			<value>com.mysql.jdbc.Driver</value>
		</property>
		<property name="url">
			<value>jdbc:mysql://127.0.0.1:3306/activiti-study?useUnicode=true&characterEncoding=UTF-8
			</value>
		</property>
		<property name="username">
			<value>root</value>
		</property>
		<property name="password" value="fadp" />
	</bean>

	<bean id="processEngine1" 
		class="org.activiti.engine.impl.cfg.StandaloneProcessEngineConfiguration">
		<property name="dataSource" ref="dataSource" />
		<property name="databaseSchemaUpdate" value="true" />
	</bean>

</beans>

获取的方法

	@Test
	public void getDefaultProcessEngine() {
		ProcessEngine processEngine = ProcessEngines.getDefaultProcessEngine();
		System.out.println(processEngine);
	}

但是这样就必须按照其要求的文件目录结构,我很不喜欢这样，我想自己定制，所以我实现的方式是,构建流程配置实例再创建流程实例

	private final String cfgXml =  System.getProperty("user.dir") + "/resource/activiti.cfg.xml";
	@Test
	public void createProcessEngineConfigurationFromResource() throws IOException {
        InputStream in = new FileInputStream(cfgXml);
		ProcessEngineConfiguration processEngineConfiguration = ProcessEngineConfiguration.createProcessEngineConfigurationFromInputStream(in,"processEngine1");
		System.out.println(processEngineConfiguration);
		ProcessEngine processEngine=processEngineConfiguration.buildProcessEngine();
		System.out.println(processEngine);
	}

activiti学习笔记(二) 获取流程实例

获取流程实例

流程实例获取的源码解析