问题

qa.md

问题点

DbStatusHelper.java

• 是否需要继承 DefCollectionHelperSupport 类？

  我的想法: 这个类在G1是用于用户界面的下拉框数据集合获取的

• 注入 ServletContext 这个对象？

  我的想法: 应该是不对，因为它只有是Web应用时，这个对象才会的。如果它不是Web应用时，这个DbStatusHelper 不就失效了。

  建议改成: 实现 ApplicationContextAwar接口

    public class DbStatusHelper  implements ApplicationContextAware {
  
      private ApplicationContext applicationContext;
  
      ...
  
            void setApplicationContext(ApplicationContext applicationContext) {
                   this.applicationContext = applicationContext
            }
  
     ... 
   } 

• apCheckSql这个属性是从外部注入，代码怎么没有使用它？

• getDbDao 这个方法里 final JdbcSupportDaoImpl dao = new JdbcSupportDaoImpl();，性能问题大。

  想一下，这个DBCheck方法一般是间隔1分钟左右被调用，多个数据源的情况下，内存开销确实有点大，性能问题。

  建议改成: 不要使用 JdbcSupportDaoImpl 这个类，而是直接把它里面调用的代码拿出来，参考：org.apache.commons.dbutils.QueryRunner.query(Connection, String, Object[], ResultSetHandler)

     public Object query(Connection conn, String sql, Object[] params,
            ResultSetHandler rsh) throws SQLException {
  
        PreparedStatement stmt = null;
        ResultSet rs = null;
        Object result = null;
  
        try {
            stmt = this.prepareStatement(conn, sql);
            this.fillStatement(stmt, params);
            rs = this.wrap(stmt.executeQuery());
            result = rsh.handle(rs);
  
        } catch (SQLException e) {
            this.rethrow(e, sql, params);
  
        } finally {
            try {
                close(rs);
            } finally {
                close(stmt);
            }
        }
  
        return result;
    }

• 针对多种数据库的检测语句的对应

  目录代码只定义了 Oracle、DB2、INFORMIX, 其它都走默认的select 1, 将来还有其它数据库怎么办？

  我的想法:

  • 定义一个接口

    public interface DatabaseDetectSQLDefine {
  
        String getDriverName();
        String getDetectSql();
    }

  • 如果有新增数据库且与现有的语句不同，则自定义实现类并把它暴露成Spring bean：

  @Component
  public class XXDetectSQLDefine implements DatabaseDetectSQLDefine  {
  
    public String getDriverName() {
        return "XX";
    }
  
     public String getDetectSql() {
        return "select 1 from dualx";
    }
  
  }

  • 修改 DbStatusHelper 类

   
  @Component("DbStatusHelper")
   public class DbStatusHelper implements ApplicationContextAware, InitializingBean{
    ...
  
       private final static Map<String, String> KNOWN_DB_DETECT_SQL = new HashMap<>();
       
  
           /* (non-Javadoc)
       * @see org.springframework.context.ApplicationContextAware#setApplicationContext(org.springframework.context.ApplicationContext)
       */
       @Override
       public void setApplicationContext(ApplicationContext applicationContext)
           throws BeansException {
           this.applicationContext = applicationContext;
       }
       
       /* (non-Javadoc)
       * @see org.springframework.beans.factory.InitializingBean#afterPropertiesSet()
       */
       @Override
       public void afterPropertiesSet() throws Exception {
               KNOWN_DB_DETECT_SQL.put(ORACLE_DRIVER, ORACLE_QUERY);
               KNOWN_DB_DETECT_SQL.put(INFORMIX_DRIVER, INFORMIX_QUERY);
               KNOWN_DB_DETECT_SQL.put(DB2_DRIVER, DB2_QUERY); 
  
               //Search from spring container.
               Map<String, DatabaseDetectSQLDefine> found = this.applicationContext.getBeansOfType(DatabaseDetectSQLDefine.class);
               for (DatabaseDetectSQLDefine item : found.values()) {
                   KNOWN_DB_DETECT_SQL.put(item.getDriverName(), item.getDetectSql);
               }
       }
  
  
       /**
       * @param ds
       * @return
       */
       private String checkStatus(DataSource ds) {
           Boolean exceptionFlg = false;
           
           try{
               String driverName = ds.getConnection().getMetaData().getDriverName();
               
               //Use different sql to check connection, depends on datasource type 
               // if(StringUtils.contains(StringUtils.lowerCase(driverName), ORACLE_DRIVER)){
               // 	Object[] ret = getDbDao(ds).getRecord(ORACLE_QUERY);
               // }else if(StringUtils.contains(StringUtils.lowerCase(driverName), INFORMIX_DRIVER)){
               // 	Object[] ret = getDbDao(ds).getRecord(INFORMIX_QUERY);
               // }else if(StringUtils.contains(StringUtils.lowerCase(driverName), DB2_DRIVER)){
               // 	Object[] ret = getDbDao(ds).getRecord(DB2_QUERY);
               // }else{
               // 	Object[] ret = getDbDao(ds).getRecord(DEFAULT_QUERY);
               // }
               this.getDetectSql(StringUtils.lowerCase(driverName !=null ? driverName : ""), );
  
           } catch(Exception e) {
               exceptionFlg = true;
           }
  
           String r_status;
           if(exceptionFlg){
               r_status = STATUS_STATUS_ERROR;
           } else {
               r_status = STATUS_STATUS_OK;
           }
           
           return r_status;
       } 
       
       private String getDetectSql(String driverName) {
           
           if(KNOWN_DB_DETECT_SQL.contains(driverName)) {
               return KNOWN_DB_DETECT_SQL.get(driverName);
           }  
           return DEFAULT_QUERY;
       } 
  
   ...
  
  
  
   }