The purpose of this guide is to detail the changes made by the version 2.0 of the Java Driver that are relevant to an upgrade from version 1.0.

We used the opportunity of a major version bump to incorporate your feedback and improve the API, to fix a number of inconsistencies and remove cruft. Unfortunately this means there are some breaking changes, but the new API should be both simpler and more complete.

The first part goes into the breaking changes made to the API (upgraders from 1.0 should review this section carefully), while the second part lists noteworthy but backward incompatible changes.

The following describes the changes for 2.0 that are breaking changes of the 1.0 API. For ease of use, we distinguish two categories of API changes: the "main" ones and the "other" ones.

The "main" API changes are the ones that are either likely to affect most upgraded apps or are incompatible changes that, even if minor, will not be detected at compile time. Upgraders are highly encouraged to check this list of "main" changes while upgrading their application to 2.0 (even though most applications are likely to be affected by only a handful of changes).

The "other" list is, well, other changes: those that are likely to affect a minor number of applications and will be detected by compile time errors anyway. It is ok to skip those initially and only come back to them if you have trouble compiling your application after an upgrade.

1. The Query class has been renamed into Statement (it was confusing to some that the BoundStatement was not a Statement).

   To allow this, the old Statement class has been renamed to RegularStatement.

2. The Cluster and Session shutdown API has changed. There is now a closeAsync that is asynchronous but returns a Future on the completion of the shutdown process.

   There is also a close shortcut that does the same but blocks. Also, close now waits for ongoing queries to complete by default (but you can force the closing of all connections if you want to).

3. NoHostAvailableException#getErrors now returns the full exception objects for each node instead of just a message. In other words, it returns a Map<InetAddress, Throwable> instead of a Map<InetAddress, String>.

4. Statement#getConsistencyLevel (previously Query#getConsistencyLevel, see first point) will now return null by default (instead of CL.ONE), with the meaning of "use the default consistency level".

   The default consistency level can now be configured through the new QueryOptions object in the cluster Configuration.

5. The Metrics class now uses the Codahale metrics library version 3 (version 2 was used previously). This new major version of the library has many API changes compared to its version 2 (see http://metrics.codahale.com/about/release-notes/ for details), which can thus impact consumers of the Metrics class. Furthermore, the default JmxReporter now includes a name specific to the cluster instance (to avoid conflicts when multiple Cluster instances are created in the same JVM). As a result, tools that were polling JMX info will have to be updated accordingly.

6. The QueryBuilder#in method now has the following special case: using QueryBuilder.in(QueryBuilder.bindMarker()) will generate the string IN ?, not IN (?) as was the case in 1.0. The reasoning being that the former syntax, made valid by https://issues.apache.org/jira/browse/CASSANDRA-4210 is a lot more useful than "IN (?)", as the latter can more simply use an equality.

   Note that if you really want to output "IN (?)" with the query builder, you can use QueryBuilder.in(QueryBuilder.raw("?")).

7. When binding values by name in BoundStatement (i.e. using the setX(String, X) methods), if more than one variable have the same name, then all values corresponding to that variable name are set instead of just the first occurrence.

8. The QueryBuilder#raw method does not automatically add quotes anymore, but rather output its result without any change (as the raw name implies).

   This means for instance that eq("x", raw(foo)) will output x = foo, not x = 'foo' (you don't need the raw method to output the latter string).

9. The QueryBuilder will now sometime use the new ability to send value as bytes instead of serializing everything to string. In general the QueryBuilder will do the right thing, but if you were calling the getQueryString() method on a Statement created with a QueryBuilder (for other reasons than to prepare a query) then the returned string may contain bind markers in place of some of the values provided (and in that case, getValues() will contain the values corresponding to those markers). If need be, it is possible to force the old behavior by using the new setForceNoValues() method.

1. Creating a Cluster instance (through Cluster#buildFrom or the Cluster.Builder#build method) does not create any connection right away anymore (and thus cannot throw a NoHostAvailableException or an AuthenticationException). Instead, the initial contact points are checked the first time a call to Cluster#connect is done. If for some reason you want to emulate the previous behavior, you can use the new method Cluster#init: Cluster.builder().build() in 1.0 is equivalent to Cluster.builder().build().init() in 2.0.
2. Methods from Metadata, KeyspaceMetadata and TableMetadata now use by default case insensitive identifiers (for keyspace, table and column names in parameter). You can double-quote an identifier if you want it to be a case sensitive one (as you would do in CQL) and there is a Metadata.quote helper method for that.
3. The TableMetadata#getClusteringKey method has been renamed TableMetadata#getClusteringColumns to match the "official" vocabulary.
4. The UnavailableException#getConsistency method has been renamed to UnavailableException#getConsistencyLevel for consistency with the method of QueryTimeoutException.
5. The RegularStatement class (ex-Statement class, see above) must now implement two additional methods: RegularStatement#getKeyspace and RegularStatement#getValues. If you had extended this class, you will have to implement those new methods, but both can return null if they are not useful in your case.
6. The Cluster.Initializer interface should now implement 2 new methods: Cluster.Initializer#getInitialListeners (which can return an empty collection) and Cluster.Initializer#getClusterName (which can return null).
7. The Metadata#getReplicas method now takes 2 arguments. On top of the partition key, you must now provide the keyspace too. The previous behavior was buggy: it's impossible to properly return the full list of replica for a partition key without knowing the keyspace since replication may depend on the keyspace).
8. The method LoadBalancingPolicy#newQueryPlan() method now takes the currently logged keyspace as 2nd argument. This information is necessary to do proper token aware balancing (see preceding point).
9. The ResultSetFuture#set and ResultSetFuture#setException methods have been removed (from the public API at least). They were never meant to be exposed publicly: a resultSetFuture is always set by the driver itself and should not be set manually.
10. The deprecated since 1.0.2 Host.HealthMonitor class has been removed. You will now need to use Host#isUp and Cluster#register if you were using that class.

This section details the biggest additions to 2.0 API wise. It is not an exhaustive list of new features in 2.0.

1. The new BatchStatement class allows to group any type of insert Statements (BoundStatement or RegularStatement) for execution as a batch. For instance, you can do something like:

   List<String> values = ...;
   PreparedStatement ps = session.prepare("INSERT INTO myTable(value) VALUES (?)");
   BatchStatement bs = new BatchStatement();
   for (String value : values)
       bs.add(ps.bind(value));
   session.execute(bs);
   

2. SimpleStatement can now take a list of values in addition to the query. This allows to do the equivalent of a prepare+execute but with only one round-trip to the server and without keeping the prepared statement after the execution.

   This is typically useful if a given query should be executed only once (i.e. you don't want to prepare it) but you also don't want to serialize all values into strings. Shortcut Session#execute() and Session#executeAsync() methods are also provided so you that you can do:

   String imgName = ...;
   ByteBuffer imgBytes = ...;
   session.execute("INSERT INTO images(name, bytes) VALUES (?, ?)", imgName, imgBytes);
   

3. SELECT queries are now "paged" under the hood. In other words, if a query yields a very large result, only the beginning of the ResultSet will be fetch initially, the rest being fetch "on-demand". In practice, this means that:

   for (Row r : session.execute("SELECT * FROM mytable"))
       ... process r ...
   

   should not timeout or OOM the server anymore even if "mytable" contains a lot of data. In general paging should be transparent for the application (as in the example above), but the implementation provides a number of knobs to fine tune the behavior of that paging:

   • the size of each "page" can be set per-query (Statement#setFetchSize())
   • the ResultSet object provides 2 methods to check the state of paging (ResultSet#getAvailableWithoutFetching and ResultSet#isFullyFetched) as well as a mean to force the pre-fetching of the next page (ResultSet#fetchMoreResults).