Update docs with Bazel Maven workflow

docs/bazel_maven_workflow.md

@@ -0,0 +1,86 @@
+# Working across Bazel and Maven
+
+Some users may need to work across Bazel and Maven projects. Particularly there are two common use cases.
+
+## Use SNAPSHOT jars produced by Maven in a Bazel project
+
+To use SNAPSHOT jars in a Bazel project just like one would in Maven, the following steps need to be taken.
+
+### The process for using SNAPSHOT jars produced by Maven
+
+1. Copy or link SNAPSHOT jar to same directory as or relative to Bazel BUILD file.
+2. Create a java_import rule that points to the SNAPSHOT jar.
+3. Replace maven_install rule in dependency list with java_import.
+4. Build and profit.
+
+#### Example
+Copy the SNAPSHOT jar.
+```
+cd $BUILD_DIR
+cp ~/.m2/repository/org/slf4j/slf4j-api/1.7.29/slf4j-api-1.7.30-SNAPSHOT.jar .
+```
+Or symlink to it. The advantage of using a link is that the jar can be updated by Maven and re-run build in Bazel.
+```
+cd $BUILD_DIR
+ln -s ~/.m2/repository/org/slf4j/slf4j-api/1.7.29/slf4j-api-1.7.30-SNAPSHOT.jar .
+```
+Create java_import rule in BUILD file. In this example, we'll use slf4j-api. This assumes that the location of the SNAPSHOT has been copied or symlinked to the same directory as the BUILD file.
+```
+java_import(
+    name = "org_slf4j_slf4j_api",
+    jars = [":slf4j-api-1.7.30-SNAPSHOT.jar"],
+)
+```
+Then, in the deps attribute replace maven_install rule for slf4j-api with the java_import that was just created.
+```
+java_library(
+    name = "fruit-api",
+    srcs = glob(["src/main/java/**/*.java"]),
+    visibility = ["//visibility:public"],
+    deps = [
+      ...
+      ":org_slf4j_slf4j_api", # instead of "@maven//:org_slf4j_slf4j_api"
+      ...
+    ],
+)
+```
+
+## Build SNAPSHOT jars with Bazel and use them in a Maven project
+Similar to above, we can generate SNAPSHOT jars using Bazel, so that they can be used in Maven projects. See below for detailed steps.
+
+#### The process for generating SNAPSHOT jars using Bazel
+1. Make code changes to the library which you want to release SNAPSHOT jar for.
+2. Build your library by running `bazel build <path to the library>`.
+3. Run `bazel run @pomgen//:update -- --package <path to the library>` to update version of your library artifact.
+4. Run `bazel run @pomgen//maven -- -a pomgen` to generate poms
+5. Run `bazel run @pomgen//maven -- -a install` to install the libraries into `~/.m2/repository`.
+6. Update the pom.xml in the consuming Maven project to use <new version>-SNAPSHOT of your library.
+
+#### Example
+Make some code changes in `examples/hello-world/healthyfoods/fruit-api`.
+
+Run bazel build.
+```
+bazel build //examples/hello-world/healthyfoods/fruit-api
+```
+Update artifact version.
+```
+bazel run @pomgen//:update -- --package examples/hello-world/healthyfoods/fruit-api
+```
+Generate pom(s).
+```
+bazel run @pomgen//maven -- -a pomgen
+```
+Install the built library into `~/.m2/repository`.
+```
+bazel run @pomgen//maven -- -a install
+```
+Then, update the pom.xml of the consuming Maven project.
+```
+<dependency>
+    <groupId>com.pomgen.example</groupId>
+    <artifactId>fruit-api</artifactId>
+    <version>1.0.0-SNAPSHOT</version>
+</dependency>
+```
+Now you can compile your Maven project, it should be using the latest SNAPSHOT jars produced by Bazel.

docs/change_detection.md

@@ -55,6 +55,8 @@ bazel run @pomgen//:update -- --package examples/hello-world \
     --new_released_version 1.0.0
 ```
 
+For more details on working with snapshot jars, see [this doc](./bazel_maven_workflow.md).
+
 ## Release Reasons
 
 pomgen query can show information about the Libraries being relased and their "release reason".  For example: