接着上篇博客，我们来谈谈java操作cassandra; 上篇博客的环境：jdk1.7 + python2.7.10 + cassandra2.2.8; 由于2.2.8没有对应的驱动文档，那么我们就用3.0的驱动文档，而驱动则用2.1.10.3版本;
驱动文档：
一、驱动下载
老规矩，创建maven工程，让maven来维护我们的jar，maven最重要的pom文件内容如下：
4.0.0 com.huawei cassandra 0.0.1-SNAPSHOT jar cassandra http://maven.apache.org UTF-8 com.datastax.cassandra cassandra-driver-core 2.1.10.3
二、session获取
我们先来看看官方给的Quick start案例
Cluster cluster = null; try { cluster = Cluster.builder() // (1) .addContactPoint("127.0.0.1") // cassandra服务器ip .withCredentials("admin", "admin") // 若没有启用账号认证，此处可以去掉 .build(); Session session = cluster.connect(); // (2) ResultSet rs = session.execute("select release_version from system.local"); // (3) Row row = rs.one(); System.out.println(row.getString("release_version")); // (4) } finally { if (cluster != null) cluster.close(); // (5) } 我们来看看代码中的(1) ~ (5)分别表示或者代表什么
(1)：Cluster对象是驱动程序的主入口点，它保存着真实Cassandra集群的状态(尤其是元数据)；Cluster是线程安全的，一个Cassandra集群创建一个Cluster的单例，整个应用用这一个单例即可
(2)：Session用来执行查询的，而且它也是线程安全的，同样也应该重复利用
(3)：利用execute来发送一个查询到Cassandra，execute返回一个Resultset(结果集),这个结果集就是必要的列的行集合(二维表，行是满足条件的记录，列是我们关注的某些字段)
(4)：从row中提取数据
(5)：当任务完成后，关闭cluster，关闭cluster的同时将会关闭它创建的全部session；这一步很重要，它会释放潜在的资源(TCP连接、线程池等)，在真实的应用中，我们应该在应用关闭(或应用卸载)的时候关闭cluster
如若大家有jdbc开发的经验，就会发现，上述代码似曾相识，上述代码中的session就相当于jdbc中的connection，是整个数据库操作的基础，那么我们将session的获取单独抽出来
View Code 拿到session了，那么请随意操作Cassandra吧！
三、cassandra基本操作
1、 创建表
在mycas下创建表student
use mycas;create table student( id int, address text, name text, age int, height int, primary key(id,address,name));insert into student(id,address,name,age,height) values(1,'guangdong','lixiao',32,172);
2、 session直接执行cql
和jdbc类似，关键是cql的拼接，下例是插入一条记录，删、改、查和这类似，不一一列举了
// 字符串注意单引号' String cql = "insert into mycas.student(id,address,name,age,height) values(" + student.getId() + ",'" + student.getAddress() + "','" + student.getName() + "'," + student.getAge() + "," + student.getHeight() + ");"; System.out.println(cql); session.execute(cql); 3、 Querybuilder
利用Querybuilder可以减轻cql的拼接，sql语句的拼接由驱动完成
查询一个student：
@Override public Student getStudentByKeys(int id, String address, String name) { Student student = null; ResultSet rs = session.execute( QueryBuilder.select("id", "address", "name", "age", "height") .from("mycas", "student") .where(QueryBuilder.eq("id", id)) .and(QueryBuilder.eq("address", address)) .and(QueryBuilder.eq("name", name))); Iterator rsIterator = rs.iterator(); if (rsIterator.hasNext()) { Row row = rsIterator.next(); student = new Student(); student.setAddress(row.getString("address")); student.setAge(row.getInt("age")); student.setHeight(row.getInt("height")); student.setId(row.getInt("id")); student.setName(row.getString("name")); } return student; }
保存一个student：
@Override public void saveStudent(Student student) { session.execute( QueryBuilder.insertInto("mycas", "student") .values(new String[]{"id", "address", "name", "age", "height"}, new Object[]{student.getId(), student.getAddress(), student.getName(), student.getAge(), student.getHeight()})); } 修改一个student:
@Override public void updateStudent(Student student) { session.execute( QueryBuilder.update("mycas", "student") .with(QueryBuilder.set("age", student.getAge())) .and(QueryBuilder.set("height", student.getHeight())) .where(QueryBuilder.eq("id", student.getId())) .and(QueryBuilder.eq("address", student.getAddress())) .and(QueryBuilder.eq("name", student.getName()))); } 删除一个student：
@Override public void removeStudent(int id, String address, String name) { session.execute(QueryBuilder.delete() .from("mycas", "student") .where(QueryBuilder.eq("id", id)) .and(QueryBuilder.eq("address", address)) .and(QueryBuilder.eq("name", name))); } 注意：驱动版本不同，Querybuilder的用法有些许不同，有些版本的某些方法变成非静态的了！
4、 类似jdbc那样使用预编译占位符
预编译的原理是怎样的了，上面的链接是驱动官方的解释，我来谈谈我的理解
当我们预编译statement的时候，Cassandra会解析query语句，缓存解析的结果并返回一个唯一的标志(PreparedStatement对象保持着这个标志的内部引用，就相当于通过标志可以获取到query语句预编译后的内容)：
当你绑定并且执行预编译statement的时候，驱动只会发送这个标志，那么Cassandra就会跳过解析query语句的过程：
所以，我们应该保证query语句只应该被预编译一次，缓存PreparedStatement 到我们的应用中（PreparedStatement 是线程安全的）；如果我们对同一个query语句预编译了多次，那么驱动会打印警告日志；如果一个query语句只执行一次，那么预编译不会提供性能上的提高，反而会降低性能，因为它是两个来回(结合上面两张图)，那么此时可以考虑用 来代替
和jdbc的预编译非常类似，我们来看看实际代码
静态cql
private static final String GET_STUDENT = "select id,address,name,age,height from mycas.student where id=? and address=? and name=?;"; private static final String SAVE_STUDENT = "insert into mycas.student(id,address,name,age,height) values(?,?,?,?,?);"; private static final String UPDATE_STUDENT = "update mycas.student set age=?, height=? where id=? and address=? and name=?;"; private static final String REMOVE_STUDENT = "delete from mycas.student where id=? and address=? and name=?;";
查询一个student
Student student = null; PreparedStatement prepareStatement = session.prepare(GET_STUDENT); BoundStatement bindStatement = new BoundStatement(prepareStatement).bind(id, address, name); ResultSet rs = session.execute(bindStatement); IteratorrsIterator = rs.iterator(); if (rsIterator.hasNext()) { Row row = rsIterator.next(); student = new Student(); student.setAddress(row.getString("address")); student.setAge(row.getInt("age")); student.setHeight(row.getInt("height")); student.setId(row.getInt("id")); student.setName(row.getString("name")); } return student;
保存一个student
PreparedStatement prepareStatement = session.prepare(SAVE_STUDENT); BoundStatement bindStatement = new BoundStatement(prepareStatement) .bind(student.getId(), student.getAddress(), student.getName(), student.getAge(), student.getHeight()); session.execute(bindStatement);
修改一个student
PreparedStatement prepareStatement = session.prepare(UPDATE_STUDENT); BoundStatement bindStatement = new BoundStatement(prepareStatement) .bind(student.getAge(), student.getHeight(), student.getId(), student.getAddress(), student.getName()); session.execute(bindStatement);
删除一个student
PreparedStatement prepareStatement = session.prepare(REMOVE_STUDENT); BoundStatement bindStatement = new BoundStatement(prepareStatement) .bind(id, address, name); session.execute(bindStatement);
5、 批量batch
public static void batch() { Session session = SessionRepository.getSession(); BoundStatement insertBind1 = new BoundStatement( session.prepare("insert into mycas.student(id,address,name,age,height) values(?,?,?,?,?);")) .bind(3, "guangxi", "huangfeihong", 67, 175); BoundStatement insertBind2 = new BoundStatement( session.prepare("insert into mycas.student(id,address,name,age,height) values(?,?,?,?,?);")) .bind(4, "hunan", "youzhibing", 26, 160); BoundStatement updateBind = new BoundStatement( session.prepare("update mycas.student set age=?, height=? where id=? and address=? and name=?;")) .bind(72, 173, 3, "guangxi", "huangfeihong"); BoundStatement deleteBind = new BoundStatement( session.prepare("delete from mycas.student where id=? and address=? and name=?;")) .bind(4, "hunan", "youzhibing"); BatchStatement batchStatement = new BatchStatement(); batchStatement.add(insertBind1); batchStatement.add(insertBind2); batchStatement.add(updateBind); batchStatement.add(deleteBind); session.execute(batchStatement); }