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Add example project
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‎.gitignore

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target/
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.idea/
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.mvn/.gradle-enterprise/
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.mvn/.develocity/
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data/timing.txt

‎.mvn/develocity.xml

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<develocity xmlns="https://www.gradle.com/develocity-maven"
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xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
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xsi:schemaLocation="https://www.gradle.com/develocity-maven https://www.gradle.com/schema/develocity-maven.xsd">
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<server>
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<url>https://dpeuniversity-develocity.gradle.com</url>
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</server>
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<buildScan>
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<!-- Optional, Add tags and values that make it easier to find the Build Scan related to this lab. -->
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<!-- See https://docs.gradle.com/develocity/maven-extension/current/#extending_build_scans -->
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<!-- for more information about adding custom information to a Build Scan -->
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<tags>
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<tag>dpeuni-maven-build-cache-deep-dive-outputs-overwrite-inputs</tag>
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</tags>
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<values>
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<value>
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<name>Course</name>
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<value>Maven Build Cache Deep Dive</value>
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</value>
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</values>
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</buildScan>
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<buildCache>
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<remote>
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<enabled>false</enabled>
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</remote>
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</buildCache>
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</develocity>

‎.mvn/extensions.xml

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<extensions>
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<extension>
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<groupId>com.gradle</groupId>
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<artifactId>develocity-maven-extension</artifactId>
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<version>1.21.4</version>
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</extension>
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</extensions>

‎.mvn/wrapper/maven-wrapper.properties

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# Licensed to the Apache Software Foundation (ASF) under one
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# or more contributor license agreements. See the NOTICE file
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# distributed with this work for additional information
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# regarding copyright ownership. The ASF licenses this file
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# to you under the Apache License, Version 2.0 (the
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# "License"); you may not use this file except in compliance
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# with the License. You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing,
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# software distributed under the License is distributed on an
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# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
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# KIND, either express or implied. See the License for the
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# specific language governing permissions and limitations
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# under the License.
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distributionUrl=https://repo.maven.apache.org/maven2/org/apache/maven/apache-maven/3.9.5/apache-maven-3.9.5-bin.zip

‎README.md

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# DPE University Training
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[<img width="10%" height="10%" src="https://user-images.githubusercontent.com/120980/174325546-8558160b-7f16-42cb-af0f-511849f22ebc.png">](https://dpeuniversity.gradle.com/)
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Checkout all the **free** Maven, Gradle, and DPE courses at the [DPE University][dpe-university]!
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## Maven Build Cache Deep Dive - Lab 05: Outputs Overwrite Inputs
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This is a hands-on exercise to go along with the [Maven Build Cache Deep Dive][course-url] training module. In this exercise you will go over the following:
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- How to deal with cache misses caused by outputs that overwrite inputs of a previously run goal.
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## Prerequisites
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- Finished going through the _Troubleshooting Build Cache Misses_ section in Maven Build Cache Deep Dive.
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- Java 11+
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Steps
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-----
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1. If you have not completed the previous labs, authenticate Maven with the Develocity server.
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> [!NOTE]
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> As part of taking this **free** course, you have access to a training instance of Develocity located at:
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> ```
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> https://dpeuniversity-develocity.gradle.com/
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> ```
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> [Sign in][develocity-url] to this Develocity server using the same account you use for the DPE University.
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>
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> This server is configured so users can only access the Build Scan® and Build Cache entries they publish.
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Run the following command and follow the instructions in your terminal:
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```shell
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./mvnw com.gradle:develocity-maven-extension:provision-access-key
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```
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> [!NOTE]
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> For more ways to authenticate, see the [authentication guide](https://docs.gradle.com/enterprise/maven-extension/#authenticating_with_gradle_enterprise) to see how to provide credentials.
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2. In this example the `data` directory represents content used by the build that _may_ be in another repository, a external application, or other resources needed by the build.
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This directory has already been added as an input, see the `pom.xml`.
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3. Run the build **multiple times**:
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```shell
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./mvnw clean install
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```
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4. Notice how the test goal was not cached (the tests run on every build). Open the Build Scan to see more details.
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Open `HelloWorldTest.java` and look at the `writeToResourcesDir` test method, this test writes to a directory that is used as an input. This changed input will cause a cache miss on the next build.
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5. Fix the test.
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While it is possible to configure Develocity to [ignore a whole file](https://docs.gradle.com/enterprise/maven-extension/#ignoring_arbitrary_files), when possible it's best to fix the cause of the problem. In this case, update the test to write to a different location (a temp directory or the `target/` dir).
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```diff
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- // resolve a file in the data dir (data/timing.txt)
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- Path timingFile = Paths.get("data/timing.txt");
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+ // resolve a file relative to the `target` directory
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+ Path timingFile = Paths.get("./target/test-output/timing.txt");
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+ Files.createDirectories(timingFile.getParent());
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```
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6. Run the build **multiple times**:
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```shell
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./mvnw clean install
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```
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After the first run the test goal will have a cache hit!
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## Solution Reference
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To see the solution to the lab, check out the [`solution`](https://github.com/gradle/outputs-overwrite-inputs-maven-build-cache-lab/commit/solution) branch of this project.
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## More Free Labs & Courses
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Be sure to check out our other **free** [courses][dpe-university] and [labs](https://github.com/gradle?q=dpe-university)!
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**Related courses:**
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- [Maven - Build Cache Deep Dive][course-url]
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- [Maven - Maintaining an Optimized Build Cache](https://dpeuniversity.gradle.com/c/42cf9d626302011526c4a0536b26af929b5bef58)
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- [Develocity - How to Use Build Scans](https://dpeuniversity.gradle.com/c/0b0b3e4a8d21709ff39074e9962eee6ca4276dc1)
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**Related labs:**
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- [Lab 01 - Using the local build cache](https://github.com/gradle/getting-started-maven-build-cache-lab)
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- [Lab 02 - Missing Inputs With Build Caching](https://github.com/gradle/missing-inputs-maven-build-cache-lab)
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- [Lab 03 - Add Build Cache Support to any Maven Plugin](https://github.com/gradle/caching-any-plugin-maven-build-cache-lab)
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- [Lab 04 - Handling Cache Misses with Normalization](https://github.com/gradle/cache-misses-maven-build-cache-lab)
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- [Lab 05 - Outputs Overwrite Inputs](https://github.com/gradle/outputs-overwrite-inputs-maven-build-cache-lab)
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- [Lab 06 - Maintaining an Optimized Build Cache](https://github.com/gradle/maintaining-optimized-cache-maven-build-cache-lab)
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[course-url]: https://dpeuniversity.gradle.com/c/47262fea1e74b719afb590d8cb3f8280bf2af732
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[dpe-university]: https://dpeuniversity.gradle.com/
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[develocity-url]: https://dpeuniversity-develocity.gradle.com/

‎data/hello.txt

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Hello Brent Spiner!

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