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); }