Manipulating the Java Classpath and Imports

The magic %classpath adds jars to the kernel. And the magics %import and %unimport control which classes are visible by default in your code (the regular import command is local to the cell where it runs.

These magics work in all the BeakerX JVM kernels.

Example

This first cell shows that you get an error if you try to import a class not built-in to BeakerX:



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import com.example.Demo

Then load a jar into the kernel:



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%classpath add jar ../resources/jar/demo.jar

After that, it imports and runs:



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import com.example.Demo
Demo demo = new Demo();
println demo.getObjectTest()

You can add multiple jars. Wildcards also work, like they normally do in the classpath (in this case the code could say ../resources/jar/*).



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%classpath add jar ../resources/jar/demo.jar
%classpath add jar ../resources/jar/BeakerXClasspathTest.jar

println com.example.Demo.staticTest();

import com.example.Demo

Demo demo = new Demo();
println demo.getObjectTest()

import com.beaker.BeakerXClasspathTest
BeakerXClasspathTest t = new BeakerXClasspathTest();
println com.beaker.BeakerXClasspathTest.staticTest;
println t.getObjectTest();
OutputCell.HIDDEN

The source code for these jars is in the repository. See Demo.java, and BeakerXClasspathTest.java

With no arguments the classpath magic prints-out all loaded jars:



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%classpath

Loading a Single Dependency with Grapes and Maven

Groovy has a dependency manager called Grape built-in and you can access it as follows:



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@Grab(group='com.google.code.gson', module='gson', version='2.2.4')
import com.google.gson.GsonBuilder
new GsonBuilder().create().toJson("Hello", System.out)

The %classpath magic also supports loading from maven central:



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%classpath add mvn com.google.code.gson gson 2.2.4
new com.google.gson.GsonBuilder().create().toJson("Hello", System.out)

You can also use gradle-like syntax to load dependencies:



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%classpath add mvn com.sun.jersey:jersey-core:1.19.4
import com.sun.jersey.api.uri.UriBuilderImpl
return new UriBuilderImpl()
            .path("http://beakerx.com/")
            .path("documentation")
            .build();

POM-Type Dependencies

Most dependencies are JARs, but a few such as Jena are POMs. They can be loaded like this:



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%classpath add mvn org.apache.jena apache-jena-libs 3.6.0 pom
model = org.apache.jena.rdf.model.ModelFactory.createDefaultModel()



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Custom Repository

The %classpath config resolver gives you able to define custom repository:



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%classpath config resolver repository.spring.snapshot http://repo.spring.io/snapshot



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%classpath add mvn org.springframework spring-context 5.0.3.BUILD-SNAPSHOT

Loading Multiple Dependencies with Maven

Use the %%classpath cell magic to load multiple dependencies at once. This magic creates a POM file containing all the dependencies listed in the cell, solves them together with Maven, and adds the result to the classpath.



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%%classpath add mvn
org.slf4j slf4j-api 1.7.25
org.slf4j slf4j-nop 1.7.25

Loading Jars from a Dynamic Location

The above magics work on literal strings. If you need to compute the location of a jar, use the dynamic classpath magic. It has two versions one that works with a single string, and another that takes a list of strings:



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location = "../resources/jar/"



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%classpath add dynamic location + "demo.jar"



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%classpath add dynamic [location + "demo.jar", location + "BeakerXClasspathTest.jar"]

Location of the Maven Cache and Using a Local Repository

Maven normally downloads jars to ~/.m2/repository/. But unfortunately this cache is not safe for concurrent access. To avoid corrupting it, BeakerX by default uses its own Maven cache in the conda environment at $(CONDA_PREFIX)/share/beakerx/maven. The M2_HOME environment variable overrides the default if set.

If you want to use a normal IDE to develop a library, publish it to your local Maven repository, and then load that library into BeakerX, you can, like this:



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%classpath config resolver mvnLocal

That is shorthand for a %classpath config resolver local magic with a file: path to the local repository.

Clearing the Maven Cache

If you have painted yourself into a corner, you can clear the contents of the maven cache as follows. This is useful for example if you have locally published non-snapshot artifacts. After resetting the cache, you will be prompted to restart your kernel.



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%classpath reset

Import and Unimport

Normally import in Groovy only works in the cell where you use it. To make a class import automatically into all cells, use %import magic.



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%import com.twosigma.beakerx.widget.IntSlider
w = new IntSlider()
w.value = 60
w



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w2 = new IntSlider()



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%unimport com.twosigma.beakerx.widget.IntSlider



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w3 = new IntSlider()



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%import static java.lang.Math.PI



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PI

More details of the implementation:



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%classpath add jar ../resources/jar/demo.jar
%classpath
5+5



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%classpath
%classpath add jar ../resources/jar/demo.jar



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%classpath add jar ../resources/jar/demo.jar
%classpath



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%import static com.example.Demo.staticTest



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staticTest()



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%import static com.example.Demo.STATIC_TEST_123



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STATIC_TEST_123



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%import static com.example.Demo.*



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STATIC_TEST_123



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staticTest()