How do I get Eclipse to resolve classes generated with Maven 2? - eclipse

Question

I'm using Google Protocol Buffers to generate some Java classes for my project. Using Maven 2 and its "antrun" plugin, these classes are freshly generated before compile, output to target/generated-sources and put on the classpath during the build. So building the project from the POM is no problem.
However, Eclipse doesn't know how to resolve the generated class, because the folder it's in doesn't seem to be on the IDE's classpath during development. I'm using m2eclipse and have it manage dependencies for me, so I had expected Maven to take care of this.
How can I get IDE support (code completion etc.) for the generated code?

Answer 1

m2eclipse supports this. First, add the path to your build path:
<plugin>
<groupId>org.codehaus.mojo</groupId>
<artifactId>build-helper-maven-plugin</artifactId>
<version>1.8</version>
<executions>
<execution>
<id>add-source</id>
<phase>generate-sources</phase>
<goals>
<goal>add-source</goal>
</goals>
<configuration>
<sources>
<source>${project.build.directory}/generated-sources/java/</source>
</sources>
</configuration>
</execution>
</executions>
</plugin>
Second, add support for that to m2e:
<pluginManagement>
<plugins>
<plugin>
<groupId>org.eclipse.m2e</groupId>
<artifactId>lifecycle-mapping</artifactId>
<version>1.0.0</version>
<configuration>
<lifecycleMappingMetadata>
<pluginExecutions>
<pluginExecution>
<pluginExecutionFilter>
<groupId>org.codehaus.mojo</groupId>
<artifactId>build-helper-maven-plugin</artifactId>
<versionRange>[1.0,)</versionRange>
<goals>
<goal>parse-version</goal>
<goal>add-source</goal>
<goal>maven-version</goal>
<goal>add-resource</goal>
<goal>add-test-resource</goal>
<goal>add-test-source</goal>
</goals>
</pluginExecutionFilter>
<action>
<execute>
<runOnConfiguration>true</runOnConfiguration>
<runOnIncremental>true</runOnIncremental>
</execute>
</action>
</pluginExecution>
</pluginExecutions>
</lifecycleMappingMetadata>
</configuration>
</plugin>
</plugins>
</pluginManagement>
The second step might not be necessary, if your eclipse installation has installed the "org.eclipse.m2e.discovery.lifecyclemapping.buildhelper.xml" plugin. This plugin is available via Window -> Preferences -> Maven -> Discovery. Currently, that does not work here at Eclipse Kepler, therefore, I fetched the JAR (linked from the xml shown in the Catalog URL) and extracted the fragments from org.eclipse.m2e.discovery.lifecyclemapping.buildhelper.xml by hand.

Answer 2

m2eclipse doesn't support this. You must manually add the folder target/generated-sources as a source folder. When you tell m2eclipse to "Update Project Configuration", this will be overwritten and you have to restore it.
Also, make sure that Eclipse looks for changes in the workspace.
There might be some issues, though. Eventually, you'll run into errors that some class can't be compiled because some other class can't be resolved. Code completion will work, though. The root cause of this issue is that Eclipse gets confused when Maven changes class files in target.
To solve this, you must tell Eclipse to compile to a different place than Maven.

Answer 3

What you should see in your project explorer is a container named "Maven Dependencies" in place of the usual "Referenced libraries". This means m2eclipse is managing your build path.
In my case, to achieve this, I checked "Include Modules" and unchecked "Skip Maven compiler plugin when processing resources" on the "Maven" section of Project->Properties.

Answer 4

Personally I resolved this problem by setting up the generated classes as a seperate project and made it a dependency in my main (non-generated) project. I was using wsdl2java to generate webservice classes so the "source" in my sub-project was the wdsl and xsds. Worked well even when the wsdl was changing regularly.

Answer 5

I had this issue with code generated using Maven and wsdl2java and here's what I did in Eclipse Juno to resolve it. Assume my project is named project1:
Right-click project1 and select Properties
Choose Java Build Path from the left and select the Libraries tab
Click Add Class Folder
Select the bin directory and click OK (project1/target/generated-sources/bin)
Click OK and Refresh the project
As an added bonus you can also attach the source code:
Click the arrow next to the new class folder you just created
Click on Source attachment
Click the Edit button
Set the Path to /project1/target/generated-sources/axis2/src
Click OK

Answer 6

Right-click project and select Properties
Choose Java Build Pathfrom the left and select the Source tab
Click Add Folder
Select the bin directory and click OK
(project/target/generated-sources/xxxx) Click OK and Refresh the project

Answer 7

How can I get IDE support (code completion etc.) for the generated code?
Typically I would add the m2e lifecycle-mapping plugin to the pom.xml file as described in #koppor's answer. However adding per-eclipse code to my pom.xml files is not an option at work which is mostly an IntelliJ shop.
My solution first adds the build-helper-maven-plugin to the pom.xml which works fine from the command line but not in eclipse.
<plugin>
<groupId>org.codehaus.mojo</groupId>
<artifactId>build-helper-maven-plugin</artifactId>
<executions>
<execution>
<phase>generate-sources</phase>
<goals>
<goal>add-source</goal>
</goals>
<configuration>
<sources>
<source>${project.build.directory}/generated-sources/</source>
</sources>
</configuration>
</execution>
</executions>
</plugin>
To fix eclipse I installed the Apt M2E Connector from the Eclipse Marketplace. I think things started working right after I restarted and then rebuilt all of my projects. I now see the following in my source dirs:
src/main/java
target/generated-sources
...
Feature!

Answer 8

Did you try to refresh the Eclipse project?
(source: oyvindhauge.com)
When an external tool generate new files or updates old ones, Eclipse will not be able to detect the change until the next request.
Another option would be to define a new Custom builder, specifying for that builder to "refresh resources upon completion":
alt text http://www.cs.lth.se/EDA180/2005/Verktyg/eclipse_refresh.gif

Answer 9

Worked for me (But you will to have to follow this every time so you can add this path in pom.xml)
Right click on your project > Build Path > Configure Build Path
In sources tag, click on [Add Folder] button
Check target/generated-sources/annotations

Answer 10

To generate Java source files from .proto files use Protocol Buffers Plugin which works out-of-the-box in eclipse Oxygen.
Basic usage (see here for detailed description):
make sure that native protoc compiler is installed on your system
update your pom.xml file:
make sure you use at least Java 6 (Java 7+ is recommended)
add plugin invocation
add the corresponding dependency for com.google.protobuf:protobuf-java
put your .proto files inside project's src/main/proto directory
update the project (via Maven -> Update project...)
Example pom.xml:
<project>
...
<build>
<plugins>
<!-- Require at least Java 6 -->
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.7.0</version>
<configuration>
<source>1.6</source>
<target>1.6</target>
</configuration>
</plugin>
<!-- Generate .java files from .proto definitions -->
<plugin>
<groupId>org.xolstice.maven.plugins</groupId>
<artifactId>protobuf-maven-plugin</artifactId>
<version>0.5.1</version>
<configuration>
<protocExecutable>/usr/local/bin/protoc</protocExecutable>
</configuration>
<executions>
<execution>
<goals>
<goal>compile</goal>
<goal>test-compile</goal>
</goals>
</execution>
</executions>
</plugin>
...
</plugins>
</build>
<dependencies>
<dependency>
<groupId>com.google.protobuf</groupId>
<artifactId>protobuf-java</artifactId>
<version>3.5.1</version>
</dependency>
...
</dependencies>
...
</project>
Some additional notes:
if protoc executable is in the PATH the protocExecutable configuration entry can be omitted
test-only protobuf message definitions can be put into project's src/test/proto directory
I recommend installing Protocol Buffer Descriptor Editor (marketplace link)
Good luck!