#1561 add support for adders in combination with streams

- Extended Type#getAlternativeTargetAccessors to recognize stream read
  accessors for which no corresponding setter exists
  (there is only an add method)
- Extended SourceRHS#getSourceTypeForMatching to return the
  correct source type for streams too
- Add StreamAdderWrapper to map Stream -> Adder
- Extended PropertyMapping$PropertyMappingBuilder#assignToPlainViaAdder
  to return StreamAdderWrapper if source type is stream

processor/src/main/java/org/mapstruct/ap/internal/model/PropertyMapping.java

@@ -25,6 +25,7 @@ import org.mapstruct.ap.internal.model.assignment.ArrayCopyWrapper;
 import org.mapstruct.ap.internal.model.assignment.EnumConstantWrapper;
 import org.mapstruct.ap.internal.model.assignment.GetterWrapperForCollectionsAndMaps;
 import org.mapstruct.ap.internal.model.assignment.SetterWrapper;
+import org.mapstruct.ap.internal.model.assignment.StreamAdderWrapper;
 import org.mapstruct.ap.internal.model.assignment.UpdateWrapper;
 import org.mapstruct.ap.internal.model.common.Assignment;
 import org.mapstruct.ap.internal.model.common.FormattingParameters;
@@ -438,6 +439,10 @@ public class PropertyMapping extends ModelElement {
             if ( result.getSourceType().isCollectionType() ) {
                 result = new AdderWrapper( result, method.getThrownTypes(), isFieldAssignment(), targetPropertyName );
             }
+            else if ( result.getSourceType().isStreamType() ) {
+                result = new StreamAdderWrapper(
+                    result, method.getThrownTypes(), isFieldAssignment(), targetPropertyName );
+            }
             else {
                 // Possibly adding null to a target collection. So should be surrounded by an null check.
                 result = new SetterWrapper( result, method.getThrownTypes(), ALWAYS, isFieldAssignment(), targetType );

processor/src/main/java/org/mapstruct/ap/internal/model/assignment/StreamAdderWrapper.java

@@ -0,0 +1,67 @@
+/*
+ * Copyright MapStruct Authors.
+ *
+ * Licensed under the Apache License version 2.0, available at http://www.apache.org/licenses/LICENSE-2.0
+ */
+package org.mapstruct.ap.internal.model.assignment;
+
+import java.util.ArrayList;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Set;
+import java.util.stream.Stream;
+
+import org.mapstruct.ap.internal.model.common.Assignment;
+import org.mapstruct.ap.internal.model.common.Type;
+import org.mapstruct.ap.internal.util.Nouns;
+
+import static org.mapstruct.ap.internal.util.Collections.first;
+
+/**
+ * Wraps the assignment in a target setter.
+ *
+ * @author Sebastian Haberey
+ */
+public class StreamAdderWrapper extends AssignmentWrapper {
+
+    private final List<Type> thrownTypesToExclude;
+    private final Type adderType;
+
+    public StreamAdderWrapper(Assignment rhs,
+                              List<Type> thrownTypesToExclude,
+                              boolean fieldAssignment,
+                              String targetPropertyName ) {
+        super( rhs, fieldAssignment );
+        this.thrownTypesToExclude = thrownTypesToExclude;
+        String desiredName = Nouns.singularize( targetPropertyName );
+        rhs.setSourceLocalVarName( rhs.createLocalVarName( desiredName ) );
+        adderType = first( getSourceType().determineTypeArguments( Stream.class ) );
+    }
+
+    @Override
+    public List<Type> getThrownTypes() {
+        List<Type> parentThrownTypes = super.getThrownTypes();
+        List<Type> result = new ArrayList<Type>( parentThrownTypes );
+        for ( Type thrownTypeToExclude : thrownTypesToExclude ) {
+            for ( Type parentExceptionType : parentThrownTypes ) {
+                if ( parentExceptionType.isAssignableTo( thrownTypeToExclude ) ) {
+                    result.remove( parentExceptionType );
+                }
+            }
+        }
+        return result;
+    }
+
+    public Type getAdderType() {
+        return adderType;
+    }
+
+    @Override
+    public Set<Type> getImportTypes() {
+        Set<Type> imported = new HashSet<Type>();
+        imported.addAll( super.getImportTypes() );
+        imported.add( adderType.getTypeBound() );
+        return imported;
+    }
+
+}

processor/src/main/java/org/mapstruct/ap/internal/model/common/SourceRHS.java

@@ -9,6 +9,7 @@ import java.util.Collection;
 import java.util.Collections;
 import java.util.List;
 import java.util.Set;
+import java.util.stream.Stream;
 
 import org.mapstruct.ap.internal.util.Strings;
 
@@ -124,8 +125,15 @@ public class SourceRHS extends ModelElement implements Assignment {
      * @return the source type to be used in the matching process.
      */
     public Type getSourceTypeForMatching() {
-        return useElementAsSourceTypeForMatching && sourceType.isCollectionType() ?
-            first( sourceType.determineTypeArguments( Collection.class ) ) : sourceType;
+        if ( useElementAsSourceTypeForMatching ) {
+            if ( sourceType.isCollectionType() ) {
+                return first( sourceType.determineTypeArguments( Collection.class ) );
+            }
+            else if ( sourceType.isStreamType() ) {
+                return first( sourceType.determineTypeArguments( Stream.class ) );
+            }
+        }
+        return sourceType;
     }
 
     /**

processor/src/main/java/org/mapstruct/ap/internal/model/common/Type.java

@@ -13,6 +13,7 @@ import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
+import java.util.stream.Stream;
 import javax.lang.model.element.AnnotationMirror;
 import javax.lang.model.element.Element;
 import javax.lang.model.element.ElementKind;
@@ -33,6 +34,7 @@ import org.mapstruct.ap.internal.prism.CollectionMappingStrategyPrism;
 import org.mapstruct.ap.internal.util.AccessorNamingUtils;
 import org.mapstruct.ap.internal.util.Executables;
 import org.mapstruct.ap.internal.util.Filters;
+import org.mapstruct.ap.internal.util.JavaStreamConstants;
 import org.mapstruct.ap.internal.util.Nouns;
 import org.mapstruct.ap.internal.util.accessor.Accessor;
 import org.mapstruct.ap.internal.util.accessor.ExecutableElementAccessor;
@@ -625,46 +627,67 @@ public class Type extends ModelElement implements Comparable<Type> {
      */
     private Accessor getAdderForType(Type collectionProperty, String pluralPropertyName) {
 
-        List<Accessor> candidates = new ArrayList<Accessor>();
-        if ( collectionProperty.isCollectionType ) {
+        List<Accessor> candidates;
 
-            // this is a collection, so this can be done always
-            TypeMirror typeArg = first( collectionProperty.determineTypeArguments( Iterable.class ) ).getTypeBound()
-                .getTypeMirror();
-            // now, look for a method that
-            // 1) starts with add,
-            // 2) and has typeArg as one and only arg
-            List<Accessor> adderList = getAdders();
-            for ( Accessor adder : adderList ) {
-                ExecutableElement executable = adder.getExecutable();
-                if ( executable == null ) {
-                    // it should not be null, but to be safe
-                    continue;
-                }
-                VariableElement arg = executable.getParameters().get( 0 );
-                if ( typeUtils.isSameType( arg.asType(), typeArg ) ) {
-                    candidates.add( adder );
-                }
-            }
+        if ( collectionProperty.isCollectionType() ) {
+            candidates = getAccessorCandidates( collectionProperty, Iterable.class );
         }
+        else if ( collectionProperty.isStreamType() ) {
+            candidates = getAccessorCandidates( collectionProperty, Stream.class );
+        }
+        else {
+            return null;
+        }
+
         if ( candidates.isEmpty() ) {
             return null;
         }
-        else if ( candidates.size() == 1 ) {
+
+        if ( candidates.size() == 1 ) {
             return candidates.get( 0 );
         }
-        else {
-            for ( Accessor candidate : candidates ) {
-                String elementName = accessorNaming.getElementNameForAdder( candidate );
-                if ( elementName != null && elementName.equals( Nouns.singularize( pluralPropertyName ) ) ) {
-                    return candidate;
-                }
+
+        for ( Accessor candidate : candidates ) {
+            String elementName = accessorNaming.getElementNameForAdder( candidate );
+            if ( elementName != null && elementName.equals( Nouns.singularize( pluralPropertyName ) ) ) {
+                return candidate;
             }
         }
 
         return null;
     }
 
+    /**
+     * Returns all accessor candidates that start with "add" and have exactly one argument
+     * whose type matches the collection or stream property's type argument.
+     *
+     * @param property the collection or stream property
+     * @param superclass the superclass to use for type argument lookup
+     *
+     * @return accessor candidates
+     */
+    private List<Accessor> getAccessorCandidates(Type property, Class<?> superclass) {
+        TypeMirror typeArg = first( property.determineTypeArguments( superclass ) ).getTypeBound()
+            .getTypeMirror();
+        // now, look for a method that
+        // 1) starts with add,
+        // 2) and has typeArg as one and only arg
+        List<Accessor> adderList = getAdders();
+        List<Accessor> candidateList = new ArrayList<Accessor>();
+        for ( Accessor adder : adderList ) {
+            ExecutableElement executable = adder.getExecutable();
+            if ( executable == null ) {
+                // it should not be null, but to be safe
+                continue;
+            }
+            VariableElement arg = executable.getParameters().get( 0 );
+            if ( typeUtils.isSameType( arg.asType(), typeArg ) ) {
+                candidateList.add( adder );
+            }
+        }
+        return candidateList;
+    }
+
     /**
      * getSetters
      *
@@ -716,7 +739,7 @@ public class Type extends ModelElement implements Comparable<Type> {
             // an accessor could substitute the setter in that case and act as setter.
             // (assuming it is initialized)
             for ( Accessor readAccessor : readAccessors ) {
-                if ( isCollectionOrMap( readAccessor ) &&
+                if ( isCollectionOrMapOrStream( readAccessor ) &&
                     !correspondingSetterMethodExists( readAccessor, setterMethods ) ) {
                     result.add( readAccessor );
                 }
@@ -745,14 +768,21 @@ public class Type extends ModelElement implements Comparable<Type> {
         return false;
     }
 
-    private boolean isCollectionOrMap(Accessor getterMethod) {
-        return isCollection( getterMethod.getAccessedType() ) || isMap( getterMethod.getAccessedType() );
+    private boolean isCollectionOrMapOrStream(Accessor getterMethod) {
+        return isCollection( getterMethod.getAccessedType() ) || isMap( getterMethod.getAccessedType() ) ||
+            isStream( getterMethod.getAccessedType() );
     }
 
     private boolean isCollection(TypeMirror candidate) {
         return isSubType( candidate, Collection.class );
     }
 
+    private boolean isStream(TypeMirror candidate) {
+        TypeElement streamTypeElement = elementUtils.getTypeElement( JavaStreamConstants.STREAM_FQN );
+        TypeMirror streamType = streamTypeElement == null ? null : typeUtils.erasure( streamTypeElement.asType() );
+        return streamType != null && typeUtils.isSubtype( candidate, streamType );
+    }
+
     private boolean isMap(TypeMirror candidate) {
         return isSubType( candidate, Map.class );
     }

processor/src/main/resources/org/mapstruct/ap/internal/model/assignment/StreamAdderWrapper.ftl

@@ -0,0 +1,14 @@
+<#--
+
+    Copyright MapStruct Authors.
+
+    Licensed under the Apache License version 2.0, available at http://www.apache.org/licenses/LICENSE-2.0
+
+-->
+<#-- @ftlvariable name="" type="org.mapstruct.ap.internal.model.assignment.StreamAdderWrapper" -->
+<#import "../macro/CommonMacros.ftl" as lib>
+<@lib.handleExceptions>
+  if ( ${sourceReference} != null ) {
+      ${sourceReference}.forEach( ${ext.targetBeanName}::${ext.targetWriteAccessorName} );
+  }
+</@lib.handleExceptions>

processor/src/test/java/org/mapstruct/ap/test/bugs/_1561/java8/Issue1561Mapper.java

@@ -0,0 +1,24 @@
+/*
+ * Copyright MapStruct Authors.
+ *
+ * Licensed under the Apache License version 2.0, available at http://www.apache.org/licenses/LICENSE-2.0
+ */
+package org.mapstruct.ap.test.bugs._1561.java8;
+
+import org.mapstruct.CollectionMappingStrategy;
+import org.mapstruct.Mapper;
+import org.mapstruct.factory.Mappers;
+
+/**
+ * @author Sebastian Haberey
+ */
+@Mapper(collectionMappingStrategy = CollectionMappingStrategy.ADDER_PREFERRED)
+public interface Issue1561Mapper {
+
+    Issue1561Mapper
+        INSTANCE = Mappers.getMapper( Issue1561Mapper.class );
+
+    Target map(Source source);
+
+    Source map(Target target);
+}

processor/src/test/java/org/mapstruct/ap/test/bugs/_1561/java8/Issue1561Test.java

@@ -0,0 +1,45 @@
+/*
+ * Copyright MapStruct Authors.
+ *
+ * Licensed under the Apache License version 2.0, available at http://www.apache.org/licenses/LICENSE-2.0
+ */
+package org.mapstruct.ap.test.bugs._1561.java8;
+
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.mapstruct.ap.testutil.IssueKey;
+import org.mapstruct.ap.testutil.WithClasses;
+import org.mapstruct.ap.testutil.runner.AnnotationProcessorTestRunner;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * @author Sebastian Haberey
+ */
+@RunWith(AnnotationProcessorTestRunner.class)
+@IssueKey("1561")
+@WithClasses({
+    Issue1561Mapper.class,
+    Source.class,
+    Target.class
+})
+public class Issue1561Test {
+
+    @Test
+    public void shouldCorrectlyUseAdder() {
+
+        Source source = new Source();
+        source.addProperty( "first" );
+        source.addProperty( "second" );
+
+        Target target = Issue1561Mapper.INSTANCE.map( source );
+
+        assertThat( target.getProperties() )
+            .containsExactly( "first", "second" );
+
+        Source mapped = Issue1561Mapper.INSTANCE.map( target );
+
+        assertThat( mapped.getProperties() )
+            .containsExactly( "first", "second" );
+    }
+}

processor/src/test/java/org/mapstruct/ap/test/bugs/_1561/java8/Source.java

@@ -0,0 +1,25 @@
+/*
+ * Copyright MapStruct Authors.
+ *
+ * Licensed under the Apache License version 2.0, available at http://www.apache.org/licenses/LICENSE-2.0
+ */
+package org.mapstruct.ap.test.bugs._1561.java8;
+
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * @author Sebastian Haberey
+ */
+public class Source {
+
+    private List<String> properties = new ArrayList<String>();
+
+    public List<String> getProperties() {
+        return properties;
+    }
+
+    public void addProperty(String property) {
+        properties.add( property );
+    }
+}

processor/src/test/java/org/mapstruct/ap/test/bugs/_1561/java8/Target.java

@@ -0,0 +1,26 @@
+/*
+ * Copyright MapStruct Authors.
+ *
+ * Licensed under the Apache License version 2.0, available at http://www.apache.org/licenses/LICENSE-2.0
+ */
+package org.mapstruct.ap.test.bugs._1561.java8;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.stream.Stream;
+
+/**
+ * @author Sebastian Haberey
+ */
+public class Target {
+
+    private List<String> properties = new ArrayList<String>();
+
+    public Stream<String> getProperties() {
+        return properties.stream();
+    }
+
+    public void addProperty(String property) {
+        properties.add( property );
+    }
+}