# Configuration Cache Requirements for your Build Logic

version 9.4.0

To capture and reload the task graph state using the Configuration Cache, Gradle enforces specific requirements on tasks and build logic. Any violation of these requirements is reported as a Configuration Cache "problem," which causes the build to fail.

In most cases, these requirements expose undeclared inputs, making builds more strict, correct, and reliable. Using the Configuration Cache is effectively an opt-in to these improvements.

The following sections describe each requirement and provide guidance on resolving issues in your build.

## Certain Types must not be Referenced by Tasks

Some types must not be referenced by task fields or in task actions (methods annotated `@TaskAction`, or the `doFirst {}` and `doLast {}` DSL blocks).

These types fall into the following categories:

- Live JVM state types

- Gradle model types

- Dependency management types

These restrictions exist because these types cannot easily be stored or reconstructed by the Configuration Cache.

### Live JVM State Types

Live JVM state types (e.g., `ClassLoader`, `Thread`, `OutputStream`, `Socket`) are disallowed, as they do not represent task inputs or outputs.

The only exceptions are standard streams (`System.in`, `System.out`, `System.err`), which can be used, for example, as parameters for `Exec` and `JavaExec` tasks.

### Gradle Model Types

Gradle model types (e.g., `Gradle`, `Settings`, `Project`, `SourceSet`, `Configuration`) are often used to pass task inputs that should instead be explicitly declared.

For example, instead of referencing a Project to retrieve `project.version` at execution time, declare the project version as a `Property<String>` input. Similarly, instead of referencing a `SourceSet` for source files or classpath resolution, declare these as a `FileCollection` input.

### Dependency Management Types

The same requirement applies to dependency management types with some nuances.

Some dependency management types, such as `Configuration` and `SourceDirectorySet`, should not be used as task inputs because they contain unnecessary state and are not precise. Use a less specific type that gives necessary features instead:

- If referencing a `Configuration` to get resolved files, declare a `FileCollection` input.

- If referencing a `SourceDirectorySet`, declare a `FileTree` input.

Additionally, referencing resolved dependency results is disallowed (e.g., `ArtifactResolutionQuery`, `ResolvedArtifact`, `ArtifactResult`). Instead:

- Use a `Provider<ResolvedComponentResult>` from `ResolutionResult.getRootComponent()`.

- Use `ArtifactCollection.getResolvedArtifacts()`, which returns a `Provider<Set<ResolvedArtifactResult>>`.

Tasks should avoid referencing resolved results and instead rely on lazy specifications to defer dependency resolution until execution time.

Some types, such as `Publication` or `Dependency`, are not serializable but could be made so in the future. Gradle may allow them as task inputs if necessary.

The following task references a `SourceSet`, which is not allowed:

build.gradle.kts

    abstract class SomeTask : DefaultTask() {

        @get:Input lateinit var sourceSet: SourceSet (1)

        @TaskAction
        fun action() {
            val classpathFiles = sourceSet.compileClasspath.files
            // ...
        }
    }

build.gradle

    abstract class SomeTask extends DefaultTask {

        @Input SourceSet sourceSet (1)

        @TaskAction
        void action() {
            def classpathFiles = sourceSet.compileClasspath.files
            // ...
        }
    }

1 | This will be reported as a problem because referencing `SourceSet` is not allowed

The following is the fixed version:

build.gradle.kts

    abstract class SomeTask : DefaultTask() {

        @get:InputFiles @get:Classpath
        abstract val classpath: ConfigurableFileCollection (1)

        @TaskAction
        fun action() {
            val classpathFiles = classpath.files
            // ...
        }
    }

build.gradle

    abstract class SomeTask extends DefaultTask {

        @InputFiles @Classpath
        abstract ConfigurableFileCollection getClasspath() (1)

        @TaskAction
        void action() {
            def classpathFiles = classpath.files
            // ...
        }
    }

1 | No more problems reported, the task now uses the supported type `ConfigurableFileCollection`

If an ad-hoc task in a script captures a disallowed reference in a `doLast {}` closure:

build.gradle.kts

    tasks.register("someTask") {
        doLast {
            val classpathFiles = sourceSets.main.get().compileClasspath.files (1)
        }
    }

build.gradle

    tasks.register('someTask') {
        doLast {
            def classpathFiles = sourceSets.main.compileClasspath.files (1)
        }
    }

1 | This will be reported as a problem because the `doLast {}` closure is capturing a reference to the `SourceSet`

You still need to fulfill the same requirement, that is, do not reference the disallowed type during task execution.

This is how the task declaration above can be fixed:

build.gradle.kts

    tasks.register("someTask") {
        val classpath = sourceSets.main.get().compileClasspath (1)
        doLast {
            val classpathFiles = classpath.files
        }
    }

build.gradle

    tasks.register('someTask') {
        def classpath = sourceSets.main.compileClasspath (1)
        doLast {
            def classpathFiles = classpath.files
        }
    }

1 | No more problems reported, the `doLast {}` closure now only captures `classpath` which is of the supported `FileCollection` type

Sometimes, a disallowed type is indirectly referenced through another type. For example, a task may reference an allowed type that, in turn, references a disallowed type. The hierarchical view in the HTML problem report can help you trace such issues and identify the offending reference.

## Using the `Project` Object at Execution Time

Tasks must not use any `Project` objects during execution. This includes calling `Task.getProject()` while a task is running.

Some cases can be resolved similarly to those described in disallowed types.

Often, equivalent functionality is available on both `Project` and `Task`. For example:

- If you need a `Logger`, use `Task.logger` instead of `Project.logger`.

- For file operations, use injected services rather than `Project` methods.

The following task incorrectly references the `Project` object at execution time:

build.gradle.kts

    abstract class SomeTask : DefaultTask() {
        @TaskAction
        fun action() {
            project.copy { (1)
                from("source")
                into("destination")
            }
        }
    }

build.gradle

    abstract class SomeTask extends DefaultTask {
        @TaskAction
        void action() {
            project.copy { (1)
                from 'source'
                into 'destination'
            }
        }
    }

1 | This will be reported as a problem because the task action is using the `Project` object at execution time

Fixed version:

build.gradle.kts

    abstract class SomeTask : DefaultTask() {

        @get:Inject abstract val fs: FileSystemOperations (1)

        @TaskAction
        fun action() {
            fs.copy {
                from("source")
                into("destination")
            }
        }
    }

build.gradle

    abstract class SomeTask extends DefaultTask {

        @Inject abstract FileSystemOperations getFs() (1)

        @TaskAction
        void action() {
            fs.copy {
                from 'source'
                into 'destination'
            }
        }
    }

1 | No more problem reported, the injected `FileSystemOperations` service is supported as a replacement for `project.copy {}`

If the same problem occurs in an ad-hoc task in a script:

build.gradle.kts

    tasks.register("someTask") {
        doLast {
            project.copy { (1)
                from("source")
                into("destination")
            }
        }
    }

build.gradle

    tasks.register('someTask') {
        doLast {
            project.copy { (1)
                from 'source'
                into 'destination'
            }
        }
    }

1 | This will be reported as a problem because the task action is using the `Project` object at execution time

Fixed version:

build.gradle.kts

    interface Injected {
        @get:Inject val fs: FileSystemOperations (1)
    }
    tasks.register("someTask") {
        val injected = project.objects.newInstance<Injected>() (2)
        doLast {
            injected.fs.copy { (3)
                from("source")
                into("destination")
            }
        }
    }

build.gradle

    interface Injected {
        @Inject FileSystemOperations getFs() (1)
    }
    tasks.register('someTask') {
        def injected = project.objects.newInstance(Injected) (2)
        doLast {
            injected.fs.copy { (3)
                from 'source'
                into 'destination'
            }
        }
    }

1 | Services can’t be injected directly in scripts, we need an extra type to convey the injection point
2 | Create an instance of the extra type using `project.object` outside the task action
3 | No more problem reported, the task action references `injected` that provides the `FileSystemOperations` service, supported as a replacement for `project.copy {}`

Fixing ad-hoc tasks in scripts requires additional effort, making it a good opportunity to refactor them into proper task classes.

The table below lists recommended replacements for commonly used `Project` methods:

Instead of: | Use:
--- | ---
`project.rootDir` | A task input or output property or a script variable to capture the result of using `project.rootDir` to calculate the actual parameter.
`project.projectDir` | A task input or output property or a script variable to capture the result of using `project.projectDir` to calculate the actual parameter.
`project.buildDir` | `project.buildDir` has been deprecated. You should use `project.layout.buildDirectory`. Use a task input or output property or a script variable to capture the result of using `project.layout.buildDirectory` to calculate the actual parameter.
`project.name` | A task input or output property or a script variable to capture the result of using `project.name` to calculate the actual parameter.
`project.description` | A task input or output property or a script variable to capture the result of using `project.description` to calculate the actual parameter.
`project.group` | A task input or output property or a script variable to capture the result of using `project.group` to calculate the actual parameter.
`project.version` | A task input or output property or a script variable to capture the result of using `project.version` to calculate the actual parameter.
`project.properties`, `project.property(name)`, `project.hasProperty(name)`, `project.getProperty(name)` or `project.findProperty(name)` | Value providers for Gradle properties.
`project.logger` | Task.logger
`project.provider {}` | ProviderFactory.provider {}
`project.file(path)` | A task input or output property or a script variable to capture the result of using `project.file(file)` to calculate the actual parameter.
`project.uri(path)` | A task input or output property or a script variable to capture the result of using `project.uri(path)` to calculate the actual parameter. Otherwise, `File.toURI()` or some other JVM API can be used.
`project.relativePath(path)` | ProjectLayout.projectDirectory.file(path)
`project.files(paths)` | ObjectFactory.fileCollection().from(paths)
`project.fileTree(paths)` | ObjectFactory.fileTree().from(dir)
`project.zipTree(path)` | ArchiveOperations.zipTree(path)
`project.tarTree(path)` | ArchiveOperations.tarTree(path)
`project.resources` | A task input or output property or a script variable to capture the result of using `project.resource` to calculate the actual parameter.
`project.copySpec {}` | FileSystemOperations.copySpec {}
`project.copy {}` | FileSystemOperations.copy {}
`project.sync {}` | FileSystemOperations.sync {}
`project.delete {}` | FileSystemOperations.delete {}
`project.mkdir(path)` | The Kotlin, Groovy or Java API available to your build logic.
`project.exec {}` | ExecOperations.exec {}
`project.javaexec {}` | ExecOperations.javaexec {}
`project.ant {}` | Task.ant
`project.createAntBuilder()` | Task.ant

## Accessing a Task Instance from Another Instance

Tasks must not directly access the state of another task instance. Instead, they should be connected using input and output relationships.

This requirement ensures that tasks remain isolated and correctly cacheable. As a result, it is unsupported to write tasks that configure other tasks at execution time.

## Sharing Mutable Objects

When storing a task in the Configuration Cache, all objects referenced through the task’s fields are serialized.

In most cases, deserialization preserves reference equality—if two fields `a` and `b` reference the same instance at configuration time, they will still reference the same instance after deserialization (`a == b`, or `a === b` in Groovy/Kotlin syntax).

However, for performance reasons, certain classes—such as `java.lang.String`, `java.io.File`, and many `java.util.Collection` implementations—are serialized without preserving reference equality. After deserialization, fields that referred to these objects may reference different but equal instances.

Consider a task that stores a user-defined object and an `ArrayList` as task fields:

build.gradle.kts

    class StateObject {
        // ...we assume there is some mutable state here, and an equals implementation...
    }

    abstract class StatefulTask : DefaultTask() {
        @get:Internal
        var stateObject: StateObject? = null

        @get:Internal
        var strings: List<String>? = null
    }

    tasks.register<StatefulTask>("checkEquality") {
        val objectValue = StateObject()
        // ...configure objectValue as needed...
        val stringsValue = arrayListOf("a", "b")

        stateObject = objectValue
        strings = stringsValue

        doLast { (1)
            println("POJO reference equality: ${stateObject === objectValue}") (2)
            println("Collection reference equality: ${strings === stringsValue}") (3)
            println("Collection equality: ${strings == stringsValue}") (4)
        }
    }

build.gradle

    class StateObject {
        // ...we assume there is some mutable state here, and an equals implementation...
    }

    abstract class StatefulTask extends DefaultTask {
        @Internal
        StateObject stateObject

        @Internal
        List<String> strings
    }

    tasks.register("checkEquality", StatefulTask) {
        def objectValue = new StateObject()
        // ...configure objectValue as needed...
        def stringsValue = ["a", "b"] as ArrayList<String>

        stateObject = objectValue
        strings = stringsValue

        doLast { (1)
            println("POJO reference equality: ${stateObject === objectValue}") (2)
            println("Collection reference equality: ${strings === stringsValue}") (3)
            println("Collection equality: ${strings == stringsValue}") (4)
        }
    }

1 | `doLast` action captures the references from the enclosing scope. These captured references are also serialized to the Configuration Cache.
2 | Compare the reference to an object of user-defined class stored in the task field and the reference captured in the `doLast` action.
3 | Compare the reference to `ArrayList` instance stored in the task field and the reference captured in the `doLast` action.
4 | Check the equality of stored and captured lists.

Without Configuration Cache, reference equality is preserved in both cases:

    $ ./gradlew --no-configuration-cache checkEquality

    > Task :checkEquality
    POJO reference equality: true
    Collection reference equality: true
    Collection equality: true

With Configuration Cache enabled, only user-defined object references remain identical. List references are different, although the lists themselves remain equal:

    $ ./gradlew --configuration-cache checkEquality

    > Task :checkEquality
    POJO reference equality: true
    Collection reference equality: false
    Collection equality: true

Best Practices:

- Avoid sharing mutable objects between configuration and execution phases.

- If sharing state is necessary, wrap it in a user-defined class.

- Do not rely on reference equality for standard Java, Groovy, Kotlin, or Gradle-defined types.

Reference equality is never preserved between tasks—each task is an isolated "realm." To share objects across tasks, use a Build Service to wrap the shared state.

## Accessing Task Extensions or Conventions

Tasks must not access conventions, extensions, or extra properties at execution time.

Instead, any value relevant to task execution should be explicitly modeled as a task property to ensure proper caching and reproducibility.

## Using Build Listeners

Plugins and build scripts must not register build listeners that are created at configuration time and triggered at execution time. This includes listeners such as `BuildListener` or `TaskExecutionListener`.

Recommended Alternatives:

- Use Build Services to handle execution-time logic.

- Register a Build Service to receive task execution notifications.

- Replace `buildFinished` listeners with dataflow actions to manage build results.

## Running External Processes

| Plugin and build scripts should avoid running external processes at configuration time.

You should avoid using these APIs for running processes during configuration:

- Java/Kotlin: `ProcessBuilder`, `Runtime.exec(…​)`, etc…​

- Groovy: `*.execute()`, etc…​

- Gradle: `ExecOperations.exec`, `ExecOperations.javaexec`, etc…​

The flexibility of these methods prevent Gradle from determining how the calls impact the build configuration, making it difficult to ensure that the Configuration Cache entry can be safely reused.

However, if running processes is required at configuration time, you can use the configuration-cache-compatible APIs detailed below.

For simpler cases, when grabbing the output of the process is enough, `providers.exec()` and `providers.javaexec()` can be used:

build.gradle.kts

    val gitVersion = providers.exec {
        commandLine("git", "--version")
    }.standardOutput.asText.get()

build.gradle

    def gitVersion = providers.exec {
        commandLine("git", "--version")
    }.standardOutput.asText.get()

For more complex cases, a custom `ValueSource` implementation with injected `ExecOperations` can be used. This `ExecOperations` instance can be used at configuration time without restrictions:

build.gradle.kts

    abstract class GitVersionValueSource : ValueSource<String, ValueSourceParameters.None> {
        @get:Inject
        abstract val execOperations: ExecOperations

        override fun obtain(): String {
            val output = ByteArrayOutputStream()
            execOperations.exec {
                commandLine("git", "--version")
                standardOutput = output
            }
            return String(output.toByteArray(), Charset.defaultCharset())
        }
    }

build.gradle

    abstract class GitVersionValueSource implements ValueSource<String, ValueSourceParameters.None> {
        @Inject
        abstract ExecOperations getExecOperations()

        String obtain() {
            ByteArrayOutputStream output = new ByteArrayOutputStream()
            execOperations.exec {
                it.commandLine "git", "--version"
                it.standardOutput = output
            }
            return new String(output.toByteArray(), Charset.defaultCharset())
        }
    }

You can also use standard Java/Kotlin/Groovy process APIs like `java.lang.ProcessBuilder` in the `ValueSource`.

The `ValueSource` implementation can then be used to create a provider with `providers.of`:

build.gradle.kts

    val gitVersionProvider = providers.of(GitVersionValueSource::class) {}
    val gitVersion = gitVersionProvider.get()

build.gradle

    def gitVersionProvider = providers.of(GitVersionValueSource.class) {}
    def gitVersion = gitVersionProvider.get()

In both approaches, if the value of the provider is used at configuration time then it will become a build configuration input. The external process will be executed for every build to determine if the Configuration Cache is `UP-TO-DATE`, so it is recommended to only call fast-running processes at configuration time. If the value changes then the cache is invalidated and the process will be run again during this build as part of the configuration phase.

## Reading System Properties and Environment Variables

Plugins and build scripts may read system properties and environment variables directly at configuration time with standard Java, Groovy, or Kotlin APIs or with the value supplier APIs. Doing so makes such variables or properties a build configuration input. Therefore, changing their value invalidates the Configuration Cache.

The Configuration Cache report includes a list of these build configuration inputs to help track them.

In general, you should avoid reading the value of system properties and environment variables at configuration time to avoid cache misses when these values change. Instead, you can connect the `Provider` returned by `providers.systemProperty()` or `providers.environmentVariable()` to task properties.

Some access patterns that potentially enumerate all environment variables or system properties (for example, calling `System.getenv().forEach()` or using the iterator of its `keySet()`) are discouraged. In this case, Gradle cannot find out what properties are actual build configuration inputs, so every available property becomes one. Even adding a new property will invalidate the cache if this pattern is used.

Using a custom predicate to filter environment variables is an example of this discouraged pattern:

build.gradle.kts

    val jdkLocations = System.getenv().filterKeys {
        it.startsWith("JDK_")
    }

build.gradle

    def jdkLocations = System.getenv().findAll {
        key, _ -> key.startsWith("JDK_")
    }

The logic in the predicate is opaque to the Configuration Cache, so all environment variables are considered inputs. One way to reduce the number of inputs is to always use methods that query a concrete variable name, such as `getenv(String)`, or `getenv().get()`:

build.gradle.kts

    val jdkVariables = listOf("JDK_8", "JDK_11", "JDK_17")
    val jdkLocations = jdkVariables.filter { v ->
        System.getenv(v) != null
    }.associate { v ->
        v to System.getenv(v)
    }

build.gradle

    def jdkVariables = ["JDK_8", "JDK_11", "JDK_17"]
    def jdkLocations = jdkVariables.findAll { v ->
        System.getenv(v) != null
    }.collectEntries { v ->
        [v, System.getenv(v)]
    }

The fixed code above, however, is not exactly equivalent to the original as only an explicit list of variables is supported. Prefix-based filtering is a common scenario, so there are provider-based APIs to access system properties and environment variables:

build.gradle.kts

    val jdkLocationsProvider = providers.environmentVariablesPrefixedBy("JDK_")

build.gradle

    def jdkLocationsProvider = providers.environmentVariablesPrefixedBy("JDK_")

Note that the Configuration Cache would be invalidated not only when the value of the variable changes or the variable is removed but also when another variable with the matching prefix is added to the environment.

For more complex use cases a custom `ValueSource` implementation can be used. System properties and environment variables referenced in the code of the `ValueSource` do not become build configuration inputs, so any processing can be applied. Instead, the value of the `ValueSource` is recomputed each time the build runs and only if the value changes the Configuration Cache is invalidated. For example, a `ValueSource` can be used to get all environment variables with names containing the substring `JDK`:

build.gradle.kts

    abstract class EnvVarsWithSubstringValueSource : ValueSource<Map<String, String>, EnvVarsWithSubstringValueSource.Parameters> {
        interface Parameters : ValueSourceParameters {
            val substring: Property<String>
        }

        override fun obtain(): Map<String, String> {
            return System.getenv().filterKeys { key ->
                key.contains(parameters.substring.get())
            }
        }
    }
    val jdkLocationsProvider = providers.of(EnvVarsWithSubstringValueSource::class) {
        parameters {
            substring = "JDK"
        }
    }

build.gradle

    abstract class EnvVarsWithSubstringValueSource implements ValueSource<Map<String, String>, Parameters> {
        interface Parameters extends ValueSourceParameters {
            Property<String> getSubstring()
        }

        Map<String, String> obtain() {
            return System.getenv().findAll { key, _ ->
                key.contains(parameters.substring.get())
            }
        }
    }
    def jdkLocationsProvider = providers.of(EnvVarsWithSubstringValueSource.class) {
        parameters {
            substring = "JDK"
        }
    }

## Undeclared Reading of Files

Plugins and build scripts should not read files directly using the Java, Groovy or Kotlin APIs at configuration time. Instead, declare files as potential build configuration inputs using the value supplier APIs.

This problem is caused by build logic similar to this:

build.gradle.kts

    val config = file("some.conf").readText()

build.gradle

    def config = file('some.conf').text

To fix this problem, read files using `providers.fileContents()` instead:

build.gradle.kts

    val config = providers.fileContents(layout.projectDirectory.file("some.conf"))
        .asText

build.gradle

    def config = providers.fileContents(layout.projectDirectory.file('some.conf'))
        .asText

In general, you should avoid reading files at configuration time, to avoid invalidating Configuration Cache entries when the file content changes. Instead, you can connect the `Provider` returned by `providers.fileContents()` to task properties.

## Bytecode Modifications and Java Agent

To detect the configuration inputs, Gradle modifies the bytecode of classes on the build script classpath, like plugins and their dependencies. Gradle uses a Java agent to modify the bytecode. Integrity self-checks of some libraries may fail because of the changed bytecode or the agent’s presence.

To work around this, you can use the Worker API with classloader or process isolation to encapsulate the library code. The bytecode of the worker’s classpath is not modified, so the self-checks should pass. When process isolation is used, the worker action is executed in a separate worker process that doesn’t have the Gradle Java agent installed.

In simple cases, when the libraries also provide command-line entry points (`public static void main()` method), you can also use the `JavaExec` task to isolate the library.

## Handling of Credentials and Secrets

Currently, the Configuration Cache does not have a built-in mechanism to prevent storing secrets used as inputs. As a result, secrets may end up in the serialized Configuration Cache entry, which, by default, is stored under `.gradle/configuration-cache` in your project directory.

To mitigate the risk of accidental exposure, Gradle encrypts the Configuration Cache. When required, Gradle transparently generates a machine-specific secret key, caches it under the `GRADLE_USER_HOME` directory, and uses it to encrypt data in the project-specific caches.

To further enhance security, follow these recommendations:

- Secure access to Configuration Cache entries.

- Use `GRADLE_USER_HOME/gradle.properties` to store secrets. The content of this file is not included in the Configuration Cache—only its fingerprint is. If storing secrets in this file, ensure access is properly restricted.

See gradle/gradle#22618.

### Providing an Encryption Key with the `GRADLE_ENCRYPTION_KEY` Environment Variable

By default, Gradle automatically generates and manages the encryption key as a Java keystore, stored under the `GRADLE_USER_HOME` directory.

For environments where this behavior is undesirable—such as when the `GRADLE_USER_HOME` directory is shared across multiple machines—you can explicitly provide an encryption key using the `GRADLE_ENCRYPTION_KEY` environment variable.

| The same encryption key must be consistently provided across multiple Gradle runs; otherwise, Gradle will be unable to reuse existing cached configurations.

### Generating an Encryption Key compatible with `GRADLE_ENCRYPTION_KEY`

To encrypt the Configuration Cache using a user-specified encryption key, Gradle requires the `GRADLE_ENCRYPTION_KEY` environment variable to be set with a valid AES key, encoded as a Base64 string.

You can generate a Base64-encoded AES-compatible key using the following command:

    $ openssl rand -base64 16

This command works on Linux and macOS, and on Windows if using a tool like Cygwin.

Once generated, set the Base64-encoded key as the value of the `GRADLE_ENCRYPTION_KEY` environment variable:

    $ export GRADLE_ENCRYPTION_KEY="your-generated-key-here"