一、介绍

使用saiku的人一定对他的元数据存储都特别感兴趣，特别是有分布式管理需求的项目，更是迫切需要了解。其实它是使用Apache的开源项目Jackrabbit管理文件的！

二、代码跟踪

我也是使用了一段时间，希望深入了解它的元数据存储，下面是代码跟踪：

2.1 ajax

首先还是从ajax入手：ajax请求：/saiku/rest/saiku/admin/datasources?_=1466478165922

对应的脚本：org.saiku.web.rest.resources.AdminResource，方法如下：

    @GET
    @Produces( {"application/json"})
    @Path("/datasources")
    @ReturnType("java.lang.List<SaikuDatasource>")
    public Response getAvailableDataSources() 

发现核心代码是：datasourceService.getDatasources().values() 不过看不出来什么，于是从代码注入开始查起！

2.2 代码注入

AdminResource对象注入：
    <bean id="adminBean" class="org.saiku.web.rest.resources.AdminResource">
        <property name="userService" ref="userServiceBean"/>
        <property name="datasourceService" ref="datasourceServiceBean"/>
        <property name="olapDiscoverService" ref="olapDiscoverServiceBean"/>
        <property name="repositoryDatasourceManager" ref="repositoryDsManager"/>
        <property name="logExtractor" ref="logwriterbean"/>
    </bean>
UserService对象注入：
    <bean id="userServiceBean" class="org.saiku.service.user.UserService">
        <property name="jdbcUserDAO" ref="userDAO"/>
        <property name="datasourceService" ref="datasourceServiceBean"/>
        <property name="iDatasourceManager" ref="repositoryDsManager"/>
        <property name="adminRoles">
            <list>
                <value>ROLE_ADMIN</value>
            </list>
        </property>
        <property name="sessionService" ref="sessionService"/>
    </bean>
DatasourceService对象注入：
    <bean id="datasourceServiceBean" class="org.saiku.service.datasource.DatasourceService">
        <property name="connectionManager" ref="connectionManager"/>
    </bean>

发现部分核心代码：

  private void readObject(ObjectInputStream stream)
      throws IOException, ClassNotFoundException {
    stream.defaultReadObject();
    datasources = connectionManager.getDataSourceManager();
  }

继续跟踪：

connectionManager对象注入：
    <bean id="connectionManager" class="org.saiku.web.core.SecurityAwareConnectionManager" init-method="init"
          destroy-method="destroy" depends-on="mondrianVFS">
        <property name="dataSourceManager" ref="repositoryDsManager"/> --这是注入执行setDataSourceManager方法，传入repositoryDsManager对象
        <property name="sessionService" ref="sessionService"/>
    </bean>
repositoryDsManager对象注入：
    <bean id="repositoryDsManager" class="org.saiku.service.datasource.RepositoryDatasourceManager" init-method="load" destroy-method="unload">
        <property name="userService" ref="userServiceBean"/>
        <property name="configurationpath" value="../../repository/configuration.xml"/>
        <property name="datadir" value="../../repository/data"/>
        <property name="foodmartdir" value="../../data"/>
        <property name="foodmartschema" value="../../data/FoodMart4.xml"/>
        <property name="foodmarturl" value="jdbc:h2:../../data/foodmart;MODE=MySQL"/>
        <property name="earthquakeDir" value="../../data"/>
        <property name="earthquakeSchema" value="../../data/Earthquakes.xml"/>
        <property name="earthquakeUrl" value="jdbc:h2:../../data/earthquakes;MODE=MySQL"/>
        <property name="repoPasswordProvider" ref ="repoPasswordProviderBean"/>
        <property name="defaultRole" value="ROLE_USER"/>
        <!-- If you change the repoPassword set this property for at least 1 restart to update the old repo password-->
        <!--<property name="oldRepoPassword" value="sa!kuanalyt!cs"/>-->
    </bean>

获取所有的元数据，就是获取RepositoryDatasourceManager对象的datasources对象，这个对象是由下面的代码生成的：

   public void load() {
        irm = JackRabbitRepositoryManager.getJackRabbitRepositoryManager(configurationpath, datadir, repopasswordprovider.getPassword(),
            oldpassword, defaultRole);
        try {
            irm.start(userService);
            this.saveInternalFile("/etc/.repo_version", "d20f0bea-681a-11e5-9d70-feff819cdc9f", null);
        } catch (RepositoryException e) {
            log.error("Could not start repo", e);
        }
        datasources.clear();
        try {

            List<DataSource> exporteddatasources = null;
            try {
                exporteddatasources = irm.getAllDataSources();
            } catch (RepositoryException e1) {
                log.error("Could not export data sources", e1);
            }

            if (exporteddatasources != null) {
                for (DataSource file : exporteddatasources) {
                    if (file.getName() != null && file.getType() != null) {
                        Properties props = new Properties();
                        SaikuDatasource.Type t = SaikuDatasource.Type.valueOf(file.getType().toUpperCase());
                        SaikuDatasource ds = new SaikuDatasource(file.getName(), t, props);
                        datasources.put(file.getName(), ds);
                    }
                }
            }
        } catch (Exception e) {
            throw new SaikuServiceException(e.getMessage(), e);
        }
    }

三、终极发现

saiku是使用JackRabbit管理树状元数据的，如果想要扩展，只能在JackRabbit基础上进行扩展，同志们继续努力！

JackRabbitIBM文档：http://www.ibm.com/developerworks/cn/java/j-jcr/
JackRabbit入门文档： http://suigara.iteye.com/blog/1454765