This is the jdbc wrapper of the DataStax Java Driver for Apache Cassandra (C*), which offers a simple JDBC compliant API to work with CQL3.
- The JDBC wrapper offers access to most of the core module features:
- Asynchronous: the driver uses the new CQL binary protocol asynchronous capabilities. Only a relatively low number of connections per nodes needs to be maintained open to achieve good performance.
- Nodes discovery: the driver automatically discovers and uses all nodes of the C* cluster, including newly bootstrapped ones.
- Configurable load balancing: the driver allows for custom routing and load balancing of queries to C* nodes. Out of the box, round robin is provided with optional data-center awareness (only nodes from the local data-center are queried (and have connections maintained to)) and optional token awareness (that is, the ability to prefer a replica for the query as coordinator).
- Transparent fail-over: if C* nodes fail or become unreachable, the driver automatically and transparently tries other nodes and schedules reconnection to the dead nodes in the background.
- Convenient schema access: the driver exposes a C* schema in a usable way.
The driver uses Cassandra's native protocol which is available starting from Cassandra 1.2. Some of the features (result set paging, BatchStatement, ...) of this version 2.0 of the driver require Cassandra 2.0 however and will throw 'unsupported feature' exceptions if used against a Cassandra 1.2 cluster.
If you are having issues connecting to the cluster (seeing NoHostAvailableConnection
exceptions) please check the connection requirements.
If you want to run the unit tests provided with this driver, you will also need to have ccm installed (http://github.com/pcmanus/ccm) as the tests use it. Also note that the first time you run the tests, ccm will download/compile the source of C* under the hood, which may require some time (that depends on your Internet connection or machine).
The last release of the driver is available on Maven Central. You can install it in your application using the following Maven dependency:
<dependency>
<groupId>com.github.adejanovski</groupId>
<artifactId>cassandra-jdbc-wrapper</artifactId>
<version>3.1.0</version>
</dependency>
Or get the fat jar with all dependencies included.
Connect to a Cassandra cluster using the following arguments:
JDBC driver class : com.github.adejanovski.cassandra.jdbc.CassandraDriver JDBC URL : jdbc:cassandra://host1--host2--host3:9042/keyspace
You can give the driver any number of host you want seperated by "--". They will be used as contact points for the driver to discover the entire cluster. Give enough hosts taking into account that some nodes may be unavailable upon establishing the JDBC connection.
Statements and prepared statements can be executed as with any JDBC driver, but queries must be expressed in CQL3.
Java sample:
Class.forName("com.github.adejanovski.cassandra.jdbc.CassandraDriver");
String URL = "jdbc:cassandra://host1--host2--host3:9042/keyspace1";
connection = DriverManager.getConnection(URL);
The default load balancing policy if not specified otherwise is TokenAwarePolicy(RoundRobinPolicy()). If you want to use another policy, add a "loadbalancing" argument to the jdbc url as follows:
jdbc:cassandra://host1--host2--host3:9042/keyspace1?loadbalancing=TokenAwarePolicy(DCAwareRoundRobinPolicy("DC1"))
Or for a Round Robin Policy:
jdbc:cassandra://host1--host2--host3:9042/keyspace1?loadbalancing=RoundRobinPolicy()
If you want to use a custom policy, give the full package of the policy's class:
jdbc:cassandra://host1--host2--host3:9042/keyspace1?loadbalancing=com.company.package.CustomPolicy()
If you want to use a policy with arguments, cast them appropriately so that the driver can use the correct types:
jdbc:cassandra://host1--host2--host3:9042/keyspace1?loadbalancing=LatencyAwarePolicy(TokenAwarePolicy(RoundRobinPolicy()),(double)10.5,(long)1,(long)10,(long)1,10)
If you want to use a retry policy, add a "retry" argument to the jdbc url as follows:
jdbc:cassandra://host1--host2--host3:9042/keyspace1?retry=DowngradingConsistencyRetryPolicy
Or for a Fallthrough Retry Policy:
jdbc:cassandra://host1--host2--host3:9042/keyspace1?retry=FallthroughRetryPolicy
If you want to use a reconnection policy, add a "reconnection" argument to the jdbc url as follows:
jdbc:cassandra://host1--host2--host3:9042/keyspace1?reconnection=ConstantReconnectionPolicy((long)10)
Make sure you cast the policy's arguments appropriately.
Consistency level can be specified per connection (not per query). To do so, add a consistency argument to the JDBC url:
jdbc:cassandra://host1--host2--host3:9042/keyspace1?consistency=LOCAL_QUORUM
Consistency level defaults to ONE if not specified.
To issue a simple select and get data from it:
statement = connection.createStatement();
ResultSet result = statement.executeQuery("SELECT bValue,iValue FROM test_table WHERE keyname='key0';");
while(result.next()){
System.out.println("bValue = " + result.getBoolean("bValue"));
System.out.println("iValue = " + result.getInt("iValue"));
};
Considering the following table:
CREATE TABLE table1
(bigint_col bigint PRIMARY KEY, ascii_col ascii , blob_col blob, boolean_col boolean,
decimal_col decimal, double_col double, float_col float, inet_col inet, int_col int,
text_col text, timestamp_col timestamp, uuid_col uuid,
timeuuid_col timeuuid, varchar_col varchar, varint_col varint,string_set_col set<text>,
string_list_col list<text>, string_map_col map<text,text>
);
Prepared statements to insert a record in "table1":
String insert = "INSERT INTO table1(bigint_col , ascii_col , blob_col , boolean_col , decimal_col , double_col , "
+ "float_col , inet_col , int_col , text_col , timestamp_col , uuid_col , timeuuid_col , varchar_col , varint_col, string_set_col, string_list_col, string_map_col) "
+ " values(?, ?, ?, ?, ?, ? , ?, ? , ? , ?, ? , ? , now(), ? , ?, ?, ?, ? );";
PreparedStatement pstatement = connection.prepareStatement(insert);
pstatement.setObject(1, 1L); // bigint
pstatement.setObject(2, "test"); // ascii
pstatement.setObject(3, new ByteArrayInputStream("test".getBytes("UTF-8"))); // blob
pstatement.setObject(4, true); // boolean
pstatement.setObject(5, new BigDecimal(5.1)); // decimal
pstatement.setObject(6, (double)5.1); // decimal
pstatement.setObject(7, (float)5.1); // inet
InetAddress inet = InetAddress.getLocalHost();
pstatement.setObject(8, inet); // inet
pstatement.setObject(9, (int)1); // int
pstatement.setObject(10, "test"); // text
pstatement.setObject(11, new Timestamp(now.getTime())); // text
UUID uuid = UUID.randomUUID();
pstatement.setObject(12, uuid ); // uuid
pstatement.setObject(13, "test"); // varchar
pstatement.setObject(14, 1);
HashSet<String> mySet = new HashSet<String>();
mySet.add("test");
mySet.add("test");
pstatement.setObject(15, mySet);
ArrayList<String> myList = new ArrayList<String>();
myList.add("test");
myList.add("test");
pstatement.setObject(16, myList);
HashMap<String,String> myMap = new HashMap<String,String>();
myMap.put("1","test");
myMap.put("2","test");
pstatement.setObject(17, myMap);
pstatement.execute();
INSERT/UPDATE
There are 2 ways to insert/update data using asynchronous queries. The first is to use JDBC batches (we're not talking about Cassandra atomic batches here).
With simple statements:
Statement statement = con.createStatement();
for(int i=0;i<10;i++){
statement.addBatch("INSERT INTO testcollection (k,L) VALUES( " + i + ",[1, 3, 12345])");
}
int[] counts = statement.executeBatch();
statement.close();
With prepared statements:
PreparedStatement statement = con.prepareStatement("INSERT INTO testcollection (k,L) VALUES(?,?)");
for(int i=0;i<10;i++){
statement.setInt(1, i);
statement.setString(2, "[1, 3, 12345]");
statement.addBatch();
}
int[] counts = statement.executeBatch();
statement.close();
The second one is to put all the queries in a single CQL statement, each ended with a semicolon (;):
Statement statement = con.createStatement();
StringBuilder queryBuilder = new StringBuilder();
for(int i=0;i<10;i++){
queryBuilder.append("INSERT INTO testcollection (k,L) VALUES( " + i + ",[1, 3, 12345]);");
}
statement.execute(queryBuilder.toString());
statement.close();
SELECT
As JDBC batches do not support returning result sets, there is only one way to send asynchronous selects through the JDBC driver:
StringBuilder queries = new StringBuilder();
for(int i=0;i<10;i++){
queries.append("SELECT * FROM testcollection where k = "+ i + ";");
}
//send all select queries at onces
ResultSet result = statement.executeQuery(queries.toString());
int nbRow = 0;
ArrayList<Integer> ids = new ArrayList<Integer>();
// get all results from all the select queries in a single result set
while(result.next()){
ids.add(result.getInt("k"));
}
Make sure you send selects that return the exact same columns or you might get pretty unpredictable results.
To create a new Tuple object in Java, use the TupleType.of().newValue() method. UDT fields cannot be instantiated outside of the Datastax Java driver core. If you want to use prepared statements, you must proceed as in the following example:
String createUDT = "CREATE TYPE IF NOT EXISTS fieldmap (key text, value text )";
String createCF = "CREATE COLUMNFAMILY t_udt (id bigint PRIMARY KEY, field_values frozen<fieldmap>, the_tuple frozen<tuple<int, text, float>>, the_other_tuple frozen<tuple<int, text, float>>);";
stmt.execute(createUDT);
stmt.execute(createCF);
stmt.close();
String insert = "INSERT INTO t_udt(id, field_values, the_tuple, the_other_tuple) values(?,{key : ?, value : ?}, (?,?,?),?);";
TupleValue t = TupleType.of(DataType.cint(), DataType.text(), DataType.cfloat()).newValue();
t.setInt(0, 1).setString(1, "midVal").setFloat(2, (float)2.0);
PreparedStatement pstatement = con.prepareStatement(insert);
pstatement.setLong(1, 1L);
pstatement.setString(2, "key1");
pstatement.setString(3, "value1");
pstatement.setInt(4, 1);
pstatement.setString(5, "midVal");
pstatement.setFloat(6, (float) 2.0);
pstatement.setObject(7, (Object)t);
pstatement.execute();
pstatement.close();
When working on collections of UDT types, it is not possible to use prepared statements. You then have to use simple statements as follows:
String createUDT = "CREATE TYPE IF NOT EXISTS fieldmap (key text, value text )";
String createCF = "CREATE COLUMNFAMILY t_udt_tuple_coll (id bigint PRIMARY KEY, field_values set<frozen<fieldmap>>, the_tuple list<frozen<tuple<int, text, float>>>, field_values_map map<text,frozen<fieldmap>>, tuple_map map<text,frozen<tuple<int,int>>>);";
stmt.execute(createUDT);
stmt.execute(createCF);
stmt.close();
System.out.println("con.getMetaData().getDatabaseProductName() = " + con.getMetaData().getDatabaseProductName());
System.out.println("con.getMetaData().getDatabaseProductVersion() = " + con.getMetaData().getDatabaseProductVersion());
System.out.println("con.getMetaData().getDriverName() = " + con.getMetaData().getDriverName());
Statement statement = con.createStatement();
String insert = "INSERT INTO t_udt_tuple_coll(id,field_values,the_tuple, field_values_map, tuple_map) values(1,{{key : 'key1', value : 'value1'},{key : 'key2', value : 'value2'}}, [(1, 'midVal1', 1.0),(2, 'midVal2', 2.0)], {'map_key1':{key : 'key1', value : 'value1'},'map_key2':{key : 'key2', value : 'value2'}}, {'tuple1':(1, 2),'tuple2':(2,3)} );";
statement.execute(insert);
statement.close();