cassandra的java操作（建表、插入数据、查询）

Cassandra是一个分布式NoSQL数据库系统，特别适合处理大量高并发的数据读写。在Java中操作Cassandra通常通过Thrift API或DataStax Java Driver（现称为DataStax Java SDK）进行。以下是基本的操作步骤：

1. **建立表** (CQL, Cassandra Query Language):

   String keyspace = "mykeyspace";
   String table = "mytable";
   String createTableQuery = "CREATE KEYSPACE IF NOT EXISTS " + keyspace + " WITH replication = {'class': 'SimpleStrategy', 'replication_factor': 3};";
   Session session = ... // 获取Session实例
   session.execute(createTableQuery);
   
   String createTableCql = "CREATE TABLE " + keyspace + "." + table + " (id UUID PRIMARY KEY, name text, age int);";
   session.execute(createTableCql);

2. **插入数据**:

   Map<String, Object> values = new HashMap<>();
   values.put("id", UUID.randomUUID());
   values.put("name", "Alice");
   values.put("age", 25);
   BatchStatement batch = new BatchStatement(BatchType.UNLOGGED);
   for (Map.Entry<String, Object> entry : values.entrySet()) {
       SimpleStatement insert = new SimpleStatement(String.format("INSERT INTO %s (%s) VALUES (%s)", table, entry.getKey(), entry.getValue()));
       batch.add(insert);
   }
   session.execute(batch);

3. **查询数据**:

   SelectStatement select = new SelectStatement(table).setConsistencyLevel(ConsistencyLevel.ONE);
   select.where(eq("id", idValue));
   ResultSet results = session.execute(select);
   Row row = results.one(); // 获取第一条数据
   System.out.println(row.getString("name")); // 输出名字