Modernize codebase with Java improvements

api/maven-api-core/src/main/java/org/apache/maven/api/JavaToolchain.java

@@ -19,6 +19,7 @@
 package org.apache.maven.api;
 
 import org.apache.maven.api.annotations.Experimental;
+import org.apache.maven.api.annotations.Nonnull;
 
 /**
  * Represents a Java toolchain in the Maven build system.
@@ -41,5 +42,6 @@
 @Experimental
 public interface JavaToolchain extends Toolchain {
 
+    @Nonnull
     String getJavaHome();
 }

api/maven-api-core/src/main/java/org/apache/maven/api/Lifecycle.java

@@ -62,13 +62,15 @@ public interface Lifecycle extends ExtensibleEnum {
      * @return the unique identifier for this lifecycle
      */
     @Override
+    @Nonnull
     String id();
 
     /**
      * Collection of main phases for this lifecycle.
      *
      * @return the collection of top-level phases in this lifecycle
      */
+    @Nonnull
     Collection<Phase> phases();
 
     /**
@@ -78,6 +80,7 @@ public interface Lifecycle extends ExtensibleEnum {
      *
      * @return the collection of phases in Maven 3 compatible ordering
      */
+    @Nonnull
     default Collection<Phase> v3phases() {
         return phases();
     }
@@ -87,6 +90,7 @@ default Collection<Phase> v3phases() {
      *
      * @return a stream of all phases in this lifecycle, including nested phases
      */
+    @Nonnull
     default Stream<Phase> allPhases() {
         return phases().stream().flatMap(Phase::allPhases);
     }
@@ -97,11 +101,12 @@ default Stream<Phase> allPhases() {
      *
      * @return the collection of phase aliases
      */
+    @Nonnull
     Collection<Alias> aliases();
 
     /**
      * A phase in the lifecycle.
-     *
+     * <p>
      * A phase is identified by its name. It also contains a list of plugins bound to that phase,
      * a list of {@link Link links}, and a list of sub-phases.  This forms a tree of phases.
      */
@@ -167,7 +172,9 @@ interface Phase {
          * @return a stream of all phases
          */
         @Nonnull
-        Stream<Phase> allPhases();
+        default Stream<Phase> allPhases() {
+            return Stream.concat(Stream.of(this), phases().stream().flatMap(Lifecycle.Phase::allPhases));
+        }
     }
 
     /**
@@ -180,13 +187,15 @@ interface Alias {
          *
          * @return the Maven 3 phase name
          */
+        @Nonnull
         String v3Phase();
 
         /**
          * Returns the Maven 4 phase name.
          *
          * @return the Maven 4 phase name
          */
+        @Nonnull
         String v4Phase();
     }
 
@@ -206,13 +215,15 @@ enum Kind {
          *
          * @return the link kind
          */
+        @Nonnull
         Kind kind();
 
         /**
          * Returns the pointer to the target phase.
          *
          * @return the phase pointer
          */
+        @Nonnull
         Pointer pointer();
     }
 
@@ -228,13 +239,15 @@ enum Type {
          *
          * @return the phase name
          */
+        @Nonnull
         String phase();
 
         /**
          * Returns the type of pointer (PROJECT, DEPENDENCIES, or CHILDREN).
          *
          * @return the pointer type
          */
+        @Nonnull
         Type type();
     }
 
@@ -244,6 +257,7 @@ interface PhasePointer extends Pointer {
          *
          * @return the PROJECT pointer type
          */
+        @Nonnull
         default Type type() {
             return Type.PROJECT;
         }
@@ -255,13 +269,15 @@ interface DependenciesPointer extends Pointer {
          *
          * @return the dependency scope, or "all" if not specified
          */
+        @Nonnull
         String scope(); // default: all
 
         /**
          * Returns the type of pointer, which is always DEPENDENCIES for a DependenciesPointer.
          *
          * @return the DEPENDENCIES pointer type
          */
+        @Nonnull
         default Type type() {
             return Type.DEPENDENCIES;
         }
@@ -273,6 +289,7 @@ interface ChildrenPointer extends Pointer {
          *
          * @return the CHILDREN pointer type
          */
+        @Nonnull
         default Type type() {
             return Type.CHILDREN;
         }

api/maven-api-core/src/main/java/org/apache/maven/api/Toolchain.java

@@ -21,6 +21,8 @@
 import java.util.Map;
 
 import org.apache.maven.api.annotations.Experimental;
+import org.apache.maven.api.annotations.Nonnull;
+import org.apache.maven.api.annotations.Nullable;
 import org.apache.maven.api.toolchain.ToolchainModel;
 
 /**
@@ -69,13 +71,15 @@ public interface Toolchain {
      *
      * @return the toolchain type
      */
+    @Nonnull
     String getType();
 
     /**
      * Gets the underlying toolchain model.
      *
      * @return the toolchain model
      */
+    @Nonnull
     ToolchainModel getModel();
 
     /**
@@ -84,7 +88,8 @@ public interface Toolchain {
      * @param toolName the tool platform independent tool name
      * @return file representing the tool executable, or null if the tool cannot be found
      */
-    String findTool(String toolName);
+    @Nullable
+    String findTool(@Nonnull String toolName);
 
     /**
      * Let the toolchain decide if it matches requirements defined
@@ -93,5 +98,5 @@ public interface Toolchain {
      * @param requirements key value pair, may not be {@code null}
      * @return {@code true} if the requirements match, otherwise {@code false}
      */
-    boolean matchesRequirements(Map<String, String> requirements);
+    boolean matchesRequirements(@Nonnull Map<String, String> requirements);
 }

api/maven-api-core/src/main/java/org/apache/maven/api/plugin/LifecycleProvider.java

@@ -22,6 +22,7 @@
 
 import org.apache.maven.api.annotations.Consumer;
 import org.apache.maven.api.annotations.Experimental;
+import org.apache.maven.api.annotations.Nonnull;
 import org.apache.maven.api.plugin.descriptor.lifecycle.Lifecycle;
 
 /**
@@ -37,5 +38,6 @@
 @Consumer
 public interface LifecycleProvider {
 
+    @Nonnull
     List<Lifecycle> getLifecycles();
 }

api/maven-api-core/src/main/java/org/apache/maven/api/plugin/Log.java

@@ -21,6 +21,8 @@
 import java.util.function.Supplier;
 
 import org.apache.maven.api.annotations.Experimental;
+import org.apache.maven.api.annotations.Nonnull;
+import org.apache.maven.api.annotations.Nullable;
 import org.apache.maven.api.annotations.Provider;
 
 /**
@@ -46,7 +48,7 @@ public interface Log {
      *
      * @param content the message to log
      */
-    void debug(CharSequence content);
+    void debug(@Nullable CharSequence content);
 
     /**
      * Sends a message (and accompanying exception) to the user in the <b>debug</b> error level.
@@ -55,19 +57,19 @@ public interface Log {
      * @param content the message to log
      * @param error the error that caused this log
      */
-    void debug(CharSequence content, Throwable error);
+    void debug(@Nullable CharSequence content, @Nullable Throwable error);
 
     /**
      * Sends an exception to the user in the <b>debug</b> error level.
      * The stack trace for this exception will be output when this error level is enabled.
      *
      * @param error the error that caused this log
      */
-    void debug(Throwable error);
+    void debug(@Nullable Throwable error);
 
-    void debug(Supplier<String> content);
+    void debug(@Nonnull Supplier<String> content);
 
-    void debug(Supplier<String> content, Throwable error);
+    void debug(@Nonnull Supplier<String> content, @Nullable Throwable error);
 
     /**
      * {@return true if the <b>info</b> error level is enabled}
@@ -79,7 +81,7 @@ public interface Log {
      *
      * @param content the message to log
      */
-    void info(CharSequence content);
+    void info(@Nullable CharSequence content);
 
     /**
      * Sends a message (and accompanying exception) to the user in the <b>info</b> error level.
@@ -88,19 +90,19 @@ public interface Log {
      * @param content the message to log
      * @param error the error that caused this log
      */
-    void info(CharSequence content, Throwable error);
+    void info(@Nullable CharSequence content, @Nullable Throwable error);
 
     /**
      * Sends an exception to the user in the <b>info</b> error level.
      * The stack trace for this exception will be output when this error level is enabled.
      *
      * @param error the error that caused this log
      */
-    void info(Throwable error);
+    void info(@Nullable Throwable error);
 
-    void info(Supplier<String> content);
+    void info(@Nonnull Supplier<String> content);
 
-    void info(Supplier<String> content, Throwable error);
+    void info(@Nonnull Supplier<String> content, @Nullable Throwable error);
 
     /**
      * {@return true if the <b>warn</b> error level is enabled}
@@ -112,7 +114,7 @@ public interface Log {
      *
      * @param content the message to log
      */
-    void warn(CharSequence content);
+    void warn(@Nullable CharSequence content);
 
     /**
      * Sends a message (and accompanying exception) to the user in the <b>warn</b> error level.
@@ -121,19 +123,19 @@ public interface Log {
      * @param content the message to log
      * @param error the error that caused this log
      */
-    void warn(CharSequence content, Throwable error);
+    void warn(@Nullable CharSequence content, @Nullable Throwable error);
 
     /**
      * Sends an exception to the user in the <b>warn</b> error level.
      * The stack trace for this exception will be output when this error level is enabled.
      *
      * @param error the error that caused this log
      */
-    void warn(Throwable error);
+    void warn(@Nullable Throwable error);
 
-    void warn(Supplier<String> content);
+    void warn(@Nonnull Supplier<String> content);
 
-    void warn(Supplier<String> content, Throwable error);
+    void warn(@Nonnull Supplier<String> content, @Nullable Throwable error);
 
     /**
      * {@return true if the <b>error</b> error level is enabled}
@@ -145,7 +147,7 @@ public interface Log {
      *
      * @param content the message to log
      */
-    void error(CharSequence content);
+    void error(@Nullable CharSequence content);
 
     /**
      * Sends a message (and accompanying exception) to the user in the <b>error</b> error level.
@@ -154,17 +156,17 @@ public interface Log {
      * @param content the message to log
      * @param error the error that caused this log
      */
-    void error(CharSequence content, Throwable error);
+    void error(@Nullable CharSequence content, @Nullable Throwable error);
 
     /**
      * Sends an exception to the user in the <b>error</b> error level.
      * The stack trace for this exception will be output when this error level is enabled.
      *
      * @param error the error that caused this log
      */
-    void error(Throwable error);
+    void error(@Nullable Throwable error);
 
-    void error(Supplier<String> content);
+    void error(@Nonnull Supplier<String> content);
 
-    void error(Supplier<String> content, Throwable error);
+    void error(@Nonnull Supplier<String> content, @Nullable Throwable error);
 }

api/maven-api-core/src/main/java/org/apache/maven/api/services/ArtifactInstaller.java

@@ -19,7 +19,7 @@
 package org.apache.maven.api.services;
 
 import java.util.Collection;
-import java.util.Collections;
+import java.util.List;
 
 import org.apache.maven.api.ProducedArtifact;
 import org.apache.maven.api.Service;
@@ -51,7 +51,7 @@ public interface ArtifactInstaller extends Service {
      *          {@code artifact} is {@code null}
      */
     default void install(Session session, ProducedArtifact artifact) {
-        install(session, Collections.singletonList(artifact));
+        install(session, List.of(artifact));
     }
 
     /**

api/maven-api-core/src/main/java/org/apache/maven/api/services/ArtifactInstallerRequest.java

@@ -19,7 +19,6 @@
 package org.apache.maven.api.services;
 
 import java.util.Collection;
-import java.util.Collections;
 import java.util.List;
 import java.util.Objects;
 
@@ -62,7 +61,7 @@ static ArtifactInstallerRequest build(Session session, Collection<ProducedArtifa
     class ArtifactInstallerRequestBuilder {
         Session session;
         RequestTrace trace;
-        Collection<ProducedArtifact> artifacts = Collections.emptyList();
+        Collection<ProducedArtifact> artifacts = List.of();
 
         ArtifactInstallerRequestBuilder() {}
 
@@ -80,7 +79,7 @@ public ArtifactInstallerRequestBuilder trace(RequestTrace trace) {
 
         @Nonnull
         public ArtifactInstallerRequestBuilder artifacts(@Nullable Collection<ProducedArtifact> artifacts) {
-            this.artifacts = artifacts != null ? artifacts : Collections.emptyList();
+            this.artifacts = artifacts != null ? artifacts : List.of();
             return this;
         }