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ScyllaDB Docs Scylla Java Driver Manual Core driver Integration

Integration¶

Quick overview¶

sample project structures for Maven and Gradle.
explanations about driver dependencies and when they can be manually excluded.

Note: guidelines to build a GraalVM native image can be found here.

Which artifact(s) should I use?¶

There are multiple driver artifacts under the group id com.datastax.oss. Here’s how to pick the right dependencies:

Feature	Artifact(s)	Comments
Core functionality: executing queries with `CqlSession.execute()`, processing the results with `ResultSet`, etc.	`java‑driver‑core`
Same as the above, but without explicit dependencies to Netty, Jackson or ESRI.	`java‑driver‑core‑shaded`	Replaces `java‑driver‑core`. See this page.
Query builder: generating CQL query strings programmatically.	`java‑driver‑query‑builder`
Object mapper: generating the boilerplate to execute queries and convert the results into your own domain classes.	`java‑driver‑mapper‑processor` `java‑driver‑mapper‑runtime`	Both artifacts are needed. See this page.
Instrumenting the driver and gathering metrics using the Micrometer metrics library.	`java‑driver‑metrics‑micrometer`	See this page.
Instrumenting the driver and gathering metrics using the MicroProfile Metrics library.	`java‑driver‑metrics‑microprofile`	See this page.
"Bill Of Materials": can help manage versions if you use multiple driver artifacts.	`java‑driver‑bom`	See this page.
Writing integration tests that run the driver against Cassandra or Simulacron.	`java‑driver‑test‑infra`	Those APIs are not covered in this manual, but you can look at the driver's contribution guidelines and internal tests for guidance.

Minimal project structure¶

We publish the driver to Maven central. Most modern build tools can download the dependency automatically.

Maven¶

Create the following 4 files:

$ find . -type f
./pom.xml
./src/main/resources/application.conf
./src/main/resources/logback.xml
./src/main/java/Main.java

Project descriptor¶

pom.xml is the Project Object Model that describes your application. We declare the dependencies, and tell Maven that we’re going to use Java 8:

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>

  <groupId>com.example.yourcompany</groupId>
  <artifactId>yourapp</artifactId>
  <version>1.0.0-SNAPSHOT</version>

  <dependencies>
    <dependency>
      <groupId>com.scylladb</groupId>
      <artifactId>java-driver-core</artifactId>
      <version>${driver.version}</version>
    </dependency>
    <dependency>
      <groupId>ch.qos.logback</groupId>
      <artifactId>logback-classic</artifactId>
      <version>1.2.3</version>
    </dependency>
  </dependencies>

  <build>
    <plugins>
      <plugin>
        <artifactId>maven-compiler-plugin</artifactId>
        <configuration>
          <source>1.8</source>
          <target>1.8</target>
        </configuration>
      </plugin>
    </plugins>
  </build>
</project>

Application configuration¶

application.conf is not stricly necessary, but it illustrates an important point about the driver’s configuration: you override any of the driver’s default options here.

datastax-java-driver {
  basic.session-name = poc
}

In this case, we just specify a custom name for our session, it will appear in the logs.

Logging configuration¶

For this example, we choose Logback as our logging framework (we added the dependency in pom.xml). logback.xml configures it to send the driver’s INFO logs to the console.

<configuration>
  <appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
    <encoder>
      <pattern>%d{HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n</pattern>
    </encoder>
  </appender>
  <root level="WARN">
    <appender-ref ref="STDOUT"/>
  </root>
  <logger name="com.datastax.oss.driver" level= "INFO"/>
</configuration>

Again, this is not strictly necessary: a truly minimal example could run without the Logback dependency, or this file; but the default behavior is a bit verbose.

Main class¶

Main.java is the canonical example introduced in our quick start; it connects to Cassandra, queries the server version and prints it:

import com.datastax.oss.driver.api.core.CqlSession;
import com.datastax.oss.driver.api.core.cql.ResultSet;

public class Main {
  public static void main(String[] args) {
    try (CqlSession session = CqlSession.builder().build()) {
      ResultSet rs = session.execute("SELECT release_version FROM system.local");
      System.out.println(rs.one().getString(0));
    }
  }
}

Make sure you have a Cassandra instance running on 127.0.0.1:9042 (otherwise, you use CqlSession.builder().addContactPoint() to use a different address).

Running¶

To launch the program from the command line, use:

$ mvn compile exec:java -Dexec.mainClass=Main

You should see output similar to:

...
[INFO] ------------------------------------------------------------------------
[INFO] Building yourapp 1.0.0-SNAPSHOT
[INFO] ------------------------------------------------------------------------
... (at this point, Maven will download the dependencies the first time) 
[INFO] --- maven-resources-plugin:2.6:resources (default-resources) @ yourapp ---
[WARNING] Using platform encoding (UTF-8 actually) to copy filtered resources, i.e. build is platform dependent!
[INFO] Copying 1 resource
[INFO]
[INFO] --- maven-compiler-plugin:2.5.1:compile (default-compile) @ yourapp ---
[INFO] Nothing to compile - all classes are up to date
[INFO]
[INFO] --- exec-maven-plugin:1.3.1:java (default-cli) @ yourapp ---
11:39:45.355 [Main.main()] INFO  c.d.o.d.i.c.DefaultMavenCoordinates - DataStax Java driver for Apache Cassandra(R) (com.datastax.oss:java-driver-core) version 4.0.1
11:39:45.648 [poc-admin-0] INFO  c.d.o.d.internal.core.time.Clock - Using native clock for microsecond precision
11:39:45.649 [poc-admin-0] INFO  c.d.o.d.i.c.metadata.MetadataManager - [poc] No contact points provided, defaulting to /127.0.0.1:9042
3.11.2
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 11.777 s
[INFO] Finished at: 2018-06-18T11:32:49-08:00
[INFO] Final Memory: 16M/277M
[INFO] ------------------------------------------------------------------------

Gradle¶

Initialize a new project with Gradle.

Modify build.gradle to add the dependencies:

group 'com.example.yourcompany'
version '1.0.0-SNAPSHOT'

apply plugin: 'java'

sourceCompatibility = 1.8

repositories {
    mavenCentral()
}

dependencies {
    compile group: 'com.datastax.oss', name: 'java-driver-core', version: '${driver.version}'
    compile group: 'ch.qos.logback', name: 'logback-classic', version: '1.2.3'
}

Then place application.conf, logback.xml and Main.java in the same locations, and with the same contents, as in the Maven example:

./src/main/resources/application.conf
./src/main/resources/logback.xml
./src/main/java/Main.java

Optionally, if you want to run from the command line, add the following at the end of build.gradle:

task execute(type:JavaExec) {
    main = 'Main'
    classpath = sourceSets.main.runtimeClasspath
}

Then launch with:

$ ./gradlew execute

You should see output similar to:

$ ./gradlew execute
:compileJava
:processResources
:classes
:execute
13:32:25.339 [main] INFO  c.d.o.d.i.c.DefaultMavenCoordinates - DataStax Java driver for Apache Cassandra(R) (com.datastax.oss:java-driver-core) version 4.0.1-alpha4-SNAPSHOT
13:32:25.682 [poc-admin-0] INFO  c.d.o.d.internal.core.time.Clock - Using native clock for microsecond precision
13:32:25.683 [poc-admin-0] INFO  c.d.o.d.i.c.metadata.MetadataManager - [poc] No contact points provided, defaulting to /127.0.0.1:9042
3.11.2

BUILD SUCCESSFUL

Manually (from the binary tarball)¶

If your build tool can’t fetch dependencies from Maven central, we publish a binary tarball on the DataStax download server.

The driver and its dependencies must be in the compile-time classpath. Application resources, such as application.conf and logback.xml in our previous examples, must be in the runtime classpath.

JPMS support¶

All the driver’s artifacts are JPMS automatic modules.

Driver dependencies¶

The driver depends on a number of third-party libraries; some of those dependencies are opt-in, while others are present by default, but may be excluded under specific circumstances.

Here’s a rundown of what you can customize:

Netty¶

Netty is the NIO framework that powers the driver’s networking layer.

It is a required dependency, but we provide a a shaded JAR that relocates it to a different Java package; this is useful to avoid dependency hell if you already use Netty in another part of your application.

Typesafe config¶

Typesafe config is used for our file-based configuration.

It is a required dependency if you use the driver’s built-in configuration loader, but this can be completely overridden with your own implementation, that could use a different framework or an ad-hoc solution.

In that case, you can exclude the dependency:

<dependency>
  <groupId>com.scylladb</groupId>
  <artifactId>java-driver-core</artifactId>
  <version>${driver.version}</version>
  <exclusions>
    <exclusion>
      <groupId>com.typesafe</groupId>
      <artifactId>config</artifactId>
    </exclusion>
  </exclusions>
</dependency>

Native libraries¶

The driver performs native calls with JNR. This is used in two cases:

to access a microsecond-precision clock in timestamp generators;
to get the process ID when generating UUIDs.

In both cases, this is completely optional; if system calls are not available on the current platform, or the library fails to load for any reason, the driver falls back to pure Java workarounds.

If you don’t want to use system calls, or already know (from looking at the driver’s logs) that they are not available on your platform, you can exclude the following dependency:

<dependency>
  <groupId>com.scylladb</groupId>
  <artifactId>java-driver-core</artifactId>
  <version>${driver.version}</version>
  <exclusions>
    <exclusion>
      <groupId>com.github.jnr</groupId>
      <artifactId>jnr-posix</artifactId>
    </exclusion>
  </exclusions>
</dependency>

Compression libraries¶

The driver supports compression with either LZ4 or Snappy.

These dependencies are optional; you have to add them explicitly in your application in order to enable compression. See the Compression page for more details.

Metrics¶

The driver exposes metrics through the Dropwizard library.

The dependency is declared as required, but metrics are optional. If you’ve disabled all metrics, or if you are using a different metrics library, and you never call Session.getMetrics anywhere in your application, then you can remove the dependency:

<dependency>
  <groupId>com.scylladb</groupId>
  <artifactId>java-driver-core</artifactId>
  <version>${driver.version}</version>
  <exclusions>
    <exclusion>
      <groupId>io.dropwizard.metrics</groupId>
      <artifactId>metrics-core</artifactId>
    </exclusion>
  </exclusions>
</dependency>

In addition, when using Dropwizard, “timer” metrics use HdrHistogram to record latency percentiles. At the time of writing, these metrics are: cql-requests, throttling.delay and cql-messages; you can also identify them by reading the comments in the configuration reference (look for “exposed as a Timer”).

If all of these metrics are disabled, or if you use a different metrics library, you can remove the dependency:

<dependency>
  <groupId>com.scylladb</groupId>
  <artifactId>java-driver-core</artifactId>
  <version>${driver.version}</version>
  <exclusions>
    <exclusion>
      <groupId>org.hdrhistogram</groupId>
      <artifactId>HdrHistogram</artifactId>
    </exclusion>
  </exclusions>
</dependency>

Jackson¶

Jackson is used:

when Insights monitoring is enabled;
when Json codecs are being used.

Jackson is declared as a required dependency, but the driver can operate normally without it. If you don’t use any of the above features, you can safely exclude the dependency:

<dependency>
  <groupId>com.scylladb</groupId>
  <artifactId>java-driver-core</artifactId>
  <version>${driver.version}</version>
  <exclusions>
    <exclusion>
      <groupId>com.fasterxml.jackson.core</groupId>
      <artifactId>*</artifactId>
    </exclusion>
  </exclusions>
</dependency>

Esri¶

The geospatial types implementation is based on the Esri Geometry API.

For driver versions >= 4.4.0 and < 4.14.0 Esri is declared as a required dependency, although the driver can operate normally without it. If you don’t use geospatial types anywhere in your application you can exclude the dependency:

<dependency>
  <groupId>com.scylladb</groupId>
  <artifactId>java-driver-core</artifactId>
  <version>${driver.version}</version>
  <exclusions>
   <exclusion>
     <groupId>com.esri.geometry</groupId>
     <artifactId>*</artifactId>
   </exclusion>
  </exclusions>
</dependency>

Starting with driver 4.14.0 Esri has been changed to an optional dependency. You no longer have to explicitly exclude the dependency if it’s not used, but if you do wish to make use of the Esri library you must now explicitly specify it as a dependency :

<dependency>
  <groupId>com.esri.geometry</groupId>
  <artifactId>esri-geometry-api</artifactId>
  <version>${esri.version}</version>
</dependency>

In the dependency specification above you should use any 1.2.x version of Esri (we recommend 1.2.1). These versions are older than the current 2.x versions of the library but they are guaranteed to be fully compatible with DSE.

TinkerPop¶

Apache TinkerPop™ is used in the graph API.

For driver versions ranging from 4.4.0 to 4.9.0 inclusive, TinkerPop is declared as a required dependency, but the driver can operate normally without it. If you don’t use the graph API at all, you can exclude the TinkerPop dependencies:

<dependency>
  <groupId>com.scylladb</groupId>
  <artifactId>java-driver-core</artifactId>
  <version>${driver.version}</version>
  <exclusions>
    <exclusion>
      <groupId>org.apache.tinkerpop</groupId>
      <artifactId>*</artifactId>
    </exclusion>
  </exclusions>
</dependency>

Starting with driver 4.10 however, TinkerPop switched to an optional dependency. Excluding TinkerPop explicitly is not required anymore if you don’t use it. If you do use the graph API though, you now need to explicitly include the dependencies below in your application:

<dependency>
  <groupId>org.apache.tinkerpop</groupId>
  <artifactId>gremlin-core</artifactId>
  <version>${tinkerpop.version}</version>
</dependency>
<dependency>
  <groupId>org.apache.tinkerpop</groupId>
  <artifactId>tinkergraph-gremlin</artifactId>
  <version>${tinkerpop.version}</version>
</dependency>

Reactive Streams¶

Reactive Streams types are referenced in our reactive API.

The Reactive Streams API is declared as a required dependency, but the driver can operate normally without it. If you never call any of the executeReactive methods, you can exclude the dependency:

<dependency>
  <groupId>com.scylladb</groupId>
  <artifactId>java-driver-core</artifactId>
  <version>${driver.version}</version>
  <exclusions>
    <exclusion>
      <groupId>org.reactivestreams</groupId>
      <artifactId>reactive-streams</artifactId>
    </exclusion>
  </exclusions>
</dependency>

Documenting annotations¶

The driver team uses annotations to document certain aspects of the code:

thread safety with Java Concurrency in Practice annotations @Immutable, @ThreadSafe, @NotThreadSafe and @GuardedBy;
nullability with SpotBugs annotations @Nullable and @NonNull.

This is mostly used during development; while these annotations are retained in class files, they serve no purpose at runtime. If you want to minimize the number of JARs in your classpath, you can exclude them:

<dependency>
  <groupId>com.scylladb</groupId>
  <artifactId>java-driver-core</artifactId>
  <version>${driver.version}</version>
  <exclusions>
    <exclusion>
      <groupId>com.github.stephenc.jcip</groupId>
      <artifactId>jcip-annotations</artifactId>
    </exclusion>
    <exclusion>
      <groupId>com.github.spotbugs</groupId>
      <artifactId>spotbugs-annotations</artifactId>
    </exclusion>
  </exclusions>
</dependency>

However, there is one case when excluding those dependencies won’t work: if you use annotation processing in your build, the Java compiler scans the entire classpath – including the driver’s classes – and tries to load all declared annotations. If it can’t find the class for an annotation, you’ll get a compiler error:

error: cannot access ThreadSafe
  class file for net.jcip.annotations.ThreadSafe not found
1 error

The workaround is to keep the dependencies.

Sometimes annotation scanning can be triggered involuntarily, if one of your dependencies declares a processor via the service provider mechanism (check the META-INF/services directory in the JARs). If you are sure that you don’t need any annotation processing, you can compile with the -proc:none option and still exclude the dependencies.

Mandatory dependencies¶

The remaining core driver dependencies are the only ones that are truly mandatory:

the native protocol layer. This is essentially part of the driver code, but was externalized for reuse in other projects;
java-driver-shaded-guava, a shaded version of Guava. It is relocated to a different package, and only used by internal driver code, so it should be completely transparent to third-party code;
the SLF4J API for logging.

ScyllaDB Java Driver is available under the Apache v2 License. ScyllaDB Java Driver is a fork of DataStax Java Driver. See Copyright here.