1

我用 hector 插入数据并用 JDBC 取回数据。

除了索引列之外,数据没有任何意义,我知道这是因为 cassandra 将数据存储为字节,然后在读取时转换它(客户端转换它)

有谁知道如何在 JDBC for cassandra 中执行此操作?

我的代码:

public static void main(String[] args) throws SQLException
    {
        Connection con = null;
        String _KS = "StringMsg";
        String _CFDef = "Tweets";

        try 
        {
            Class.forName("org.apache.cassandra.cql.jdbc.CassandraDriver");
            con = DriverManager.getConnection("jdbc:cassandra://localhost:9160/" + _KS);

            String query = "SELECT username, email, msg, id FROM " + _CFDef + " WHERE 'username'='LTodorov'";

            Statement stmt = con.createStatement();
            ResultSet result = stmt.executeQuery(query);

            System.out.println("hi");
            int i=0;
            while (result.next())
            {
                System.out.println(result.getString("id"));
                System.out.println(result.getString("username"));
                System.out.println(result.getString("msg"));
                System.out.println(result.getString("email"));
                System.out.print("count:" + i + "\n\n");i++;
            }
        } 
        catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
        catch (SQLException e) {
            e.printStackTrace();
        }
        finally 
        {
            if (con != null) 
            {
                try 
                {
                    con.close();
                } 
                catch (SQLException e) 
                {
                    e.printStackTrace();
                }
                con = null;
            }
        }
    }

结果:

hi
java.nio.HeapByteBuffer[pos=237 lim=258 cap=798]
LTodorov
java.nio.HeapByteBuffer[pos=184 lim=209 cap=798]
java.nio.HeapByteBuffer[pos=144 lim=155 cap=798]
count:0

命令行结果:

GET Tweets Where username=LTodorov;
-------------------
RowKey: LTodorov1330045080096
=> (column=email, value=6c5f6c74404162762e6267, timestamp=1330045080214000)
=> (column=id, value=4c546f646f726f7631333330303435303830303936, timestamp=13300
45080098000)
=> (column=msg, value=54686973206973206d616b696e67206d652073616466616365, timest
amp=1330045080210000)
=> (column=username, value=LTodorov, timestamp=1330045080217000)

带有“假设推文验证器为 utf8”的 Cli 结果;

RowKey: LTodorov1330045080096
=> (column=email, value=l_ld@Abv.bg, timestamp=1330045080214000)
=> (column=id, value=LTodorov1330045080096, timestamp=1330045080098000)
=> (column=msg, value=This is making me sadface, timestamp=1330045080210000)
=> (column=username, value=LTodorov, timestamp=1330045080217000)

列族定义:

CREATE COLUMN FAMILY Tweets
WITH comparator = UTF8Type
AND key_validation_class=UTF8Type
AND column_metadata = [
{column_name: id, validation_class: UTF8Type}
{column_name: email, validation_class: UTF8Type}
{column_name: msg, validation_class: UTF8Type}
{column_name: user, validation_class: UTF8Type}

任何 cassandra 大师有任何指示吗?我正在取回数据,但它应该在 java 中进行转换,还是应该由 JDBC api 完成工作,还是 cassandra 的事情?(我认为这不能由 cassandra 解决)

4

2 回答 2

2

我认为你应该能够在你的java类中做到这一点。结果集返回一些数据类型,查看方法getBytes()。您可以将字节值重建为String。例如

String string_username = new String(result.getBytes("username"), "UTF-8");
System.out.println(string_username);
于 2012-02-24T03:15:03.433 回答
0

对我来说,这看起来像是 JDBC 驱动程序中的一个错误。如果 CLI 中的列是 UTF8Type(即 CQL 中的 text/varchar 类型),那么您应该能够只使用 ResultSet.getString。

您可以向http://code.google.com/a/apache-extras.org/p/cassandra-jdbc/issues/list报告 JDBC 错误

于 2012-02-27T22:09:14.820 回答