【小笔记】Activiti扩展数据库支持类型

r囧r小猫 2023-02-20 07:56 44阅读 0赞

### 场景 ###

项目需要使用GaussDB，Activiti默认支持的数据库中不包含GaussDB，需要对其进行扩展。

### 分析 ###

在其源码`org.activiti.engine.impl.cfg.ProcessEngineConfigurationImpl.getDefaultDatabaseTypeMappings()`中，写明了支持的数据库的类型：

h2、hsql、mysql、oracle、postgres、mssql、db2

并在初始化时进行了初始化：

protected static Properties databaseTypeMappings = getDefaultDatabaseTypeMappings();
    
    public void initDatabaseType() { 
    	...
    	省略内容
    	...
    }

如果获取到的数据库类型不在支持列表中，则会抛错：

connection = this.dataSource.getConnection();
                DatabaseMetaData databaseMetaData = connection.getMetaData();
                String databaseProductName = databaseMetaData.getDatabaseProductName();
    this.databaseType = databaseTypeMappings.getProperty(databaseProductName);
                if (this.databaseType == null) { 
                    throw new ActivitiException("couldn't deduct database type from database product name '" + databaseProductName + "'");
                }

查看它的实现类，发现有个Spring实现的：

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所以继承这个SpringProcesEnineConfiguration，重写一下`initDatabaseType()`，将其注入为Bean，即可进行扩展。

### 实现 ###

**重写`initDatabaseType()`：**

public class SpringProcessEngineConfigurationWithGauss extends SpringProcessEngineConfiguration { 
        private static Logger log = LoggerFactory.getLogger(SpringProcessEngineConfigurationWithGauss.class);
    
        private static Properties databaseTypeMappings = getDefaultDatabaseTypeMappings();
    
        public static Properties getDefaultDatabaseTypeMappings() { 
            Properties databaseTypeMappings = new Properties();
            ...
            省略其他
    		...
            databaseTypeMappings.setProperty("Zenith", "Zenith");
            return databaseTypeMappings;
        }
    
        @Override
        public void initDatabaseType() { 
            Connection connection = null;
    
            try { 
                connection = this.dataSource.getConnection();
                DatabaseMetaData databaseMetaData = connection.getMetaData();
                String databaseProductName = databaseMetaData.getDatabaseProductName();
                log.debug("database product name: '{}'", databaseProductName);
                this.databaseType = databaseTypeMappings.getProperty(databaseProductName);
                if (this.databaseType == null) { 
                    throw new ActivitiException("couldn't deduct database type from database product name '" + databaseProductName + "'");
                }
    
                log.debug("using database type: {}", this.databaseType);
                if ("mssql".equals(this.databaseType)) { 
                    this.maxNrOfStatementsInBulkInsert = this.DEFAULT_MAX_NR_OF_STATEMENTS_BULK_INSERT_SQL_SERVER;
                }
            } catch (SQLException var12) { 
                log.error("Exception while initializing Database connection", var12);
            } finally { 
                try { 
                    if (connection != null) { 
                        connection.close();
                    }
                } catch (SQLException var11) { 
                    log.error("Exception while closing the Database connection", var11);
                }
    
            }
        }
    }

**将其注入：**

@Bean
        public SpringProcessEngineConfigurationWithGauss processEngineConfiguration() { 
            SpringProcessEngineConfigurationWithGauss configuration = new SpringProcessEngineConfigurationWithGauss();
            ...
            省略其他配置
    		...
            return configuration;
    
        }

其次需要在activiti的包里新增一个文件：

`org\activiti\db\properties\`下新增Zenith.properties配置文件，主要作用是为不同数据库配置分页语法，GuassDB是支持类似Mysql的分页的，所以直接使用Mysql的即可。内容如下：

limitAfter=LIMIT #{maxResults} OFFSET #{firstResult}

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