Question

我想知道如何将Resultset对象强制转换为用户定义的列表类型或java中的用户定义对象。

我尝试过很多东西，但仍然卡住了。

**这是我迄今为止尝试过的方法的代码：

public List getOutBoundMessageListFromCassandra(){
   List<XchangeOutboundMessage> list=new ArrayList();
   try {

       cluster = Cluster.builder().addContactPoint(contactPoints).build();

       session = cluster.connect(keySpaceName);

       cassandraOps = new CassandraTemplate(session);

       Select s = QueryBuilder.select().from("XchangeOutboundMessage");
       ResultSet result = session.execute(s);
       list=result.all();
   } catch (Exception e) {
       e.printStackTrace();
   }
   return list;

}

Answer 1

让我们假设你有桌子：

CREATE TABLE xchangeoutboundmessage (
    id timeuuid PRIMARY KEY,
    message text,
    sender bigint
);

和Associated DTO

public class XchangeOutboundMessage {

    private UUID id;
    private String message;
    private long sender;

    public UUID getId() {
        return id;
    }

    public String getMessage() {
        return message;
    }

    public long getSender() {
        return sender;
    }

    public void setId(UUID id) {
        this.id = id;
    }

    public void setMessage(String message) {
        this.message = message;
    }

    public void setSender(long sender) {
        this.sender = sender;
    }

    @Override
    public String toString() {
        return "XchangeOutboundMessage{" + "id=" + id + ", message=" + message + ", sender=" + sender + '}';
    }

}

您可以手动从行获取日期并将值设置为dto，也可以使用cassandra-driver-mapping为您执行此操作。

使用手动映射：

for (Row row : result) {
    XchangeOutboundMessage message = new XchangeOutboundMessage();
    message.setId(row.getUUID("id"));
    message.setMessage(row.getString("message"));
    message.setSender(row.getLong("sender"));
    list.add(message);
}

使用cassandra驱动程序映射：

首先将@Table(name = "XchangeOutboundMessage")注释添加到XchangeOutboundMessage DTO

MappingManager manager = new MappingManager(session);
Mapper<XchangeOutboundMessage> mapper =  manager.mapper(XchangeOutboundMessage.class);
list = mapper.map(result).all();

注意：cassandra-driver-mapping需要添加为依赖

顺便说一下，这些类型的查询在cassandra中非常低效，总是尝试在where子句中提供分区键。

我如何在用户定义的java类对象或ArrayLIst中转换cassandra的Resultset对象

1 个答案: