Question

上下文：Spring数据cassandra官方1.0.2.RELEASE来自Maven Central repo，CQL3，cassandra 2.0，datastax driver 2.0.4

背景：cassandra blob数据类型映射到Java ByteBuffer。

下面的示例代码演示了您不会使用等效插入旁边的select来检索正确的字节。实际检索的数据以许多垃圾字节为前缀，实际上看起来像是整行的序列化。与Cassandra 1.2相关的这个older post表明我们可能必须从长度为ByteBuffer.remaining（）的ByteBuffer.arrayOffset（）开始，但是arrayOffset值实际为0.

我发现了一个spring-data-cassandra 2.0.0。 SNAPSHOT但CassandraOperations API有很大的不同，它的包名也是：org.springdata ...与org.springframework ...

帮助解决这个问题但非常欢迎。

与此同时，我似乎必须将Base64的二进制数据编码/解码到文本数据类型列中。

---这里是我使用的简单表CQL元数据-------------

CREATE TABLE person (
  id text,
  age int,
  name text,
  pict blob,
  PRIMARY KEY (id)
) ;

---跟随映射到CQL表的简单数据对象---

package org.spring.cassandra.example; 

import java.nio.ByteBuffer;
import org.springframework.data.cassandra.mapping.PrimaryKey; 
import org.springframework.data.cassandra.mapping.Table; 

@Table 
public class Person { 

 @PrimaryKey 
 private String id; 

 private int age; 
 private String name; 
 private ByteBuffer pict; 

 public Person(String id, int age, String name, ByteBuffer pict) { 
  this.id = id; this.name = name; this.age = age; this.pict = pict;
 } 

 public String getId() { return id; } 
 public String getName() { return name; } 
 public int getAge() { return age; } 
 public ByteBuffer getPict() { return pict; } 

 } 

}

---以及简单地插入和检索人物对象的普通java应用程序代码 -

package org.spring.cassandra.example;

import java.nio.ByteBuffer;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
import org.springframework.data.cassandra.core.CassandraOperations;

import com.datastax.driver.core.ResultSet;
import com.datastax.driver.core.Row;
import com.datastax.driver.core.querybuilder.QueryBuilder;
import com.datastax.driver.core.querybuilder.Select;

public class CassandraApp {

    private static final Logger logger = LoggerFactory
            .getLogger(CassandraApp.class);

    public static String hexDump(ByteBuffer bb) {
        char[] hexArray = "0123456789ABCDEF".toCharArray();
        bb.rewind();
        char[] hexChars = new char[bb.limit() * 2];
        for ( int j = 0; j < bb.limit(); j++ ) {
            int v = bb.get() & 0xFF;
            hexChars[j * 2] = hexArray[v >>> 4];
            hexChars[j * 2 + 1] = hexArray[v & 0x0F];
        }
        bb.rewind();
        return new String(hexChars);
    }

    public static void main(String[] args) {

        ApplicationContext applicationContext = new ClassPathXmlApplicationContext("app-context.xml");

        try {

            CassandraOperations cassandraOps = applicationContext.getBean(
                    "cassandraTemplate", CassandraOperations.class);

            cassandraOps.truncate("person");
            // prepare data
            byte[] ba = { 0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x11, 0x22, 0x33, 0x44, 0x55, (byte) 0xAA, (byte) 0xCC, (byte) 0xFF };
            ByteBuffer myPict = ByteBuffer.wrap(ba);
            String myId = "1234567890";
            String myName = "mickey";
            int myAge = 50;

            logger.info("We try id=" + myId + ", name=" + myName + ", age=" + myAge +", pict=" + hexDump(myPict));

            cassandraOps.insert(new Person(myId, myAge, myName, myPict ));

            Select s = QueryBuilder.select("id","name","age","pict").from("person");
            s.where(QueryBuilder.eq("id", myId));

            ResultSet rs = cassandraOps.query(s);
            Row r = rs.one();

            logger.info("We got id=" + r.getString(0) + ", name=" + r.getString(1) + ", age=" + r.getInt(2) +", pict=" + hexDump(r.getBytes(3)));

        } catch (Exception e) {
            e.printStackTrace();
        }

    }
}

---假设您为cassandra配置了一个简单的Spring项目正如http://projects.spring.io/spring-data-cassandra/

所述

实际执行产生（滑动这些记录器跟踪以查看结束）：

[main] INFO org.spring.cassandra.example.CassandraApp - 我们尝试id = 1234567890，name = mickey，age = 50，pict = 0001020304051122334455AACCFF

[主要] INFO org.spring.cassandra.example.CassandraApp - 我们得到了ID = 1234567890，姓名=米奇，年龄= 50，PICT = 8200000800000073000000020000000100000004000A6D796B657973706163650006706572736F6E00026964000D00046E616D65000D000361676500090004706963740003000000010000000A31323334353637383930000000066D69636B657900000004000000320000000E的 0001020304051122334455AACCFF

虽然插件在数据库本身看起来是正确的，如cqlsh命令行所示：

cqlsh:mykeyspace> select * from person;

 id         | age | name   | pict
------------+-----+--------+--------------------------------
 1234567890 |  50 | mickey | 0x0001020304051122334455aaccff

(1 rows)

Answer 1

我有完全相同的问题，但幸运的是找到了解决方案。问题是ByteBuffer的使用令人困惑。尝试做类似的事情：

ByteBuffer bb = resultSet.one().getBytes("column_name");
byte[] data = new byte[bb.remaining()];
bb.get(data);

感谢Sylvain在此提出的建议：http://grokbase.com/t/cassandra/user/134brvqzd3/blobs-in-cql

Answer 2

查看Datastax Java Driver的Bytes类，它提供了对数据进行编码/解码所需的内容。

在this post中我写了一个用法示例。

HTH，卡罗

Spring数据Cassandra 2.0 Select BLOB列返回不正确的ByteBuffer数据

2 个答案: