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我想缓存一些数据在风暴螺栓,但不知道如果这是正确的方式来做到这一点。在下面的类中,员工ID和工作人员名称被缓存到哈希映射。为此,对Employee表进行了一次数据库调用,以选择所有员工,并在准备方法中填充哈希映射(这是初始化映射的正确位置?)。 (在运行风暴拓扑时),拓扑正在进行多个数据库连接并且多次初始化映射。当然,我想避免这种情况,这就是为什么我要缓存结果,以便它不会每次都进入数据库。请帮忙?在风暴螺栓缓存
public class TestBolt extends BaseRichBolt {
private static final long serialVersionUID = 2946379346389650348L;
private OutputCollector collector;
private Map<String, String> employeeIdToNameMap;
private static final Logger LOG = Logger.getLogger(TestBolt.class);
@Override
public void execute(Tuple tuple) {
String employeeId = tuple.getStringByField("employeeId");
String employeeName = employeeIdToNameMap.get(employeeId);
collector.emit(tuple, new Values(employeeId, employeeName));
collector.ack(tuple);
}
@Override
public void prepare(Map stormConf, TopologyContext context, OutputCollector collector) {
// TODO Auto-generated method stub
this.collector = collector;
try {
employeeIdToNameMap = createEmployeIdToNameMap();
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
@Override
public void declareOutputFields(OutputFieldsDeclarer declarer) {
declarer.declare(new Fields(/*some fields*/));
}
private Map<String, String> createEmployeIdToNameMap() throws SQLException {
final Map<String, String> employeeIdToNameMap = new HashMap<>();
final DatabaseManager dbm = new PostgresManager();
final String query = "select id, name from employee;";
final Connection conn = dbm.createDefaultConnection();
final ResultSet result = dbm.executeSelectQuery(conn, query);
while(result.next()) {
String employeId = result.getString("id");
String name = result.getString("name");
employeeIdToNameMap.put(employeId, name);
}
conn.close();
return employeeIdToNameMap;
}
}
SOLUTION 我创建同步映射及其对我
private static Map<String, String> employeeIdToNameMap = Collections
.synchronizedMap(new HashMap<String, String>());
代码看起来不错。您在prepare()中初始化HashMap的方法绝对正确。关于到数据库的多重连接:我假设在拓扑中有多个螺栓实例(即parallelim_hint> 1)。因此,每个实例都会打开它自己的连接,这是合理的。 –
我在此螺栓旁有多个其他螺栓,其平行度> 1,但对于此螺栓,其平行度为1 – big