java实现cassandra高级操作之分页实例（有项目具体需求）

// At initialization:
Cluster cluster = Cluster.builder()
  .addContactPoint("127.0.0.1")
  .withQueryOptions(new QueryOptions().setFetchSize(2000))
  .build();

// Or at runtime:
cluster.getConfiguration().getQueryOptions().setFetchSize(2000);

Statement statement = new SimpleStatement("your query");
statement.setFetchSize(2000);

ResultSet rs = session.execute("your query");
for (Row row : rs) {
  if (rs.getAvailableWithoutFetching() == 100 && !rs.isFullyFetched())
    rs.fetchMoreResults(); // this is asynchronous
  // Process the row ...
  System.out.println(row);
}

ResultSet resultSet = session.execute("your query");
// iterate the result set...
PagingState pagingState = resultSet.getExecutionInfo().getPagingState();

// PagingState对象可以被序列化成字符串或字节数组
String string = pagingState.toString();
byte[] bytes = pagingState.toBytes();

PagingState.fromBytes(byte[] bytes);
PagingState.fromString(String str);

import java.util.Map;

import com.datastax.driver.core.PagingState;

public interface ICassandraPage
{
  Map<String, Object> page(PagingState pagingState);

}

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import com.datastax.driver.core.PagingState;
import com.datastax.driver.core.ResultSet;
import com.datastax.driver.core.Row;
import com.datastax.driver.core.Session;
import com.datastax.driver.core.SimpleStatement;
import com.datastax.driver.core.Statement;
import com.huawei.cassandra.dao.ICassandraPage;
import com.huawei.cassandra.factory.SessionRepository;
import com.huawei.cassandra.model.Teacher;

public class CassandraPageDao implements ICassandraPage
{
  private static final Session session = SessionRepository.getSession();
  
  private static final String CQL_TEACHER_PAGE = "select * from mycas.teacher;";
  
  @Override
  public Map<String, Object> page(PagingState pagingState)
  {
    final int RESULTS_PER_PAGE = 2;
    Map<String, Object> result = new HashMap<String, Object>(2);
    List<Teacher> teachers = new ArrayList<Teacher>(RESULTS_PER_PAGE);

    Statement st = new SimpleStatement(CQL_TEACHER_PAGE);
    st.setFetchSize(RESULTS_PER_PAGE);
    
    // 第一页没有分页状态
    if (pagingState != null)
    {      
      st.setPagingState(pagingState);
    }
    
    ResultSet rs = session.execute(st);
    result.put("pagingState", rs.getExecutionInfo().getPagingState());
    
    //请注意，我们不依赖RESULTS_PER_PAGE，因为fetch size并不意味着cassandra总是返回准确的结果集
    //它可能返回比fetch size稍微多一点或者少一点，另外，我们可能在结果集的结尾
    int remaining = rs.getAvailableWithoutFetching();
    for (Row row : rs)
    {
      Teacher teacher = this.obtainTeacherFromRow(row);
      teachers.add(teacher);
      
      if (--remaining == 0) 
      {
        break;
      }
    }
    result.put("teachers", teachers);
    return result;
  }

  private Teacher obtainTeacherFromRow(Row row)
  {
    Teacher teacher = new Teacher();
    teacher.setAddress(row.getString("address"));
    teacher.setAge(row.getInt("age"));
    teacher.setHeight(row.getInt("height"));
    teacher.setId(row.getInt("id"));
    teacher.setName(row.getString("name"));
    
    return teacher;
  }
 
}

import java.util.Map;

import com.datastax.driver.core.PagingState;
import com.huawei.cassandra.dao.ICassandraPage;
import com.huawei.cassandra.dao.impl.CassandraPageDao;

public class PagingTest
{
  
  public static void main(String[] args)
  {
    ICassandraPage cassPage = new CassandraPageDao();
    Map<String, Object> result = cassPage.page(null);
    PagingState pagingState = (PagingState) result.get("pagingState");
    System.out.println(result.get("teachers"));
    while (pagingState != null)
    {
      // PagingState对象可以被序列化成字符串或字节数组
      System.out.println("==============================================");
      result = cassPage.page(pagingState);
      pagingState = (PagingState) result.get("pagingState");
      System.out.println(result.get("teachers"));
    }
  }
  
}