make sure Filter predicates are always serializable

CHANGELOG.md

@@ -20,6 +20,7 @@ import org.heigit.ohsome.oshdb.api.db.OSHDBH2;
 ### other changes
 
 * integrate [ohsome-filter](https://gitlab.gistools.geog.uni-heidelberg.de/giscience/big-data/ohsome/libs/ohsome-filter) module fully into this repository, renaming it to `oshdb-filter`. ([#306])
+* make sure predicate-filters are always serializable. ([#353])
 * improve maintainability of parts of important central processing algorithms for determining entity modification history: refactoring improves code structure, adds inline documentation and enhances test coverage. ([#327])
 
 ### bugfixes
@@ -34,7 +35,7 @@ import org.heigit.ohsome.oshdb.api.db.OSHDBH2;
 [#327]: https://github.com/GIScience/oshdb/issues/327
 [#338]: https://github.com/GIScience/oshdb/issues/338
 [#352]: https://github.com/GIScience/oshdb/pull/352
-
+[#353]: https://github.com/GIScience/oshdb/pull/353
 
 ## 0.6.3
 

oshdb-api/src/main/java/org/heigit/ohsome/oshdb/api/mapreducer/MapAggregator.java

@@ -36,6 +36,7 @@
 import org.heigit.ohsome.oshdb.api.object.OSHDBMapReducible;
 import org.heigit.ohsome.oshdb.api.object.OSMContribution;
 import org.heigit.ohsome.oshdb.api.object.OSMEntitySnapshot;
+import org.heigit.ohsome.oshdb.filter.Filter;
 import org.heigit.ohsome.oshdb.filter.FilterExpression;
 import org.heigit.ohsome.oshdb.osm.OSMEntity;
 import org.heigit.ohsome.oshdb.osm.OSMType;
@@ -290,8 +291,9 @@ public MapAggregator<U, X> osmType(Set<OSMType> typeFilter) {
    *
    * @param f the filter function to call for each osm entity
    * @return a modified copy of this object (can be used to chain multiple commands together)
-   * @deprecated use oshdb-filter {@link #filter(FilterExpression)} with
-   *             {@link org.heigit.ohsome.oshdb.filter.Filter#byOSMEntity(Predicate)} instead
+   * @deprecated use oshdb-filter {@link #filter(FilterExpression)} with {@link
+   *             org.heigit.ohsome.oshdb.filter.Filter#byOSMEntity(Filter.SerializablePredicate)}
+   *             instead
    */
   @Deprecated
   @Contract(pure = true)

oshdb-api/src/main/java/org/heigit/ohsome/oshdb/api/mapreducer/MapReducer.java

@@ -431,8 +431,9 @@ public MapReducer<X> osmType(Set<OSMType> typeFilter) {
    *
    * @param f the filter function to call for each osm entity
    * @return a modified copy of this mapReducer (can be used to chain multiple commands together)
-   * @deprecated use oshdb-filter {@link #filter(FilterExpression)} with
-   *             {@link org.heigit.ohsome.oshdb.filter.Filter#byOSMEntity(Predicate)} instead
+   * @deprecated use oshdb-filter {@link #filter(FilterExpression)} with {@link
+   *             org.heigit.ohsome.oshdb.filter.Filter#byOSMEntity(Filter.SerializablePredicate)}
+   *             instead
    */
   @Deprecated
   @Contract(pure = true)

oshdb-filter/src/main/java/org/heigit/ohsome/oshdb/filter/Filter.java

@@ -1,5 +1,6 @@
 package org.heigit.ohsome.oshdb.filter;
 
+import java.io.Serializable;
 import java.util.function.BiPredicate;
 import java.util.function.Predicate;
 import java.util.function.Supplier;
@@ -12,6 +13,12 @@
  * A filter condition which can be applied to an OSM entity.
  */
 public interface Filter extends FilterExpression {
+  /** A predicate which is also serializable. */
+  public interface SerializablePredicate<T> extends Predicate<T>, Serializable {}
+
+  /** A bi-predicate which is also serializable. */
+  interface SerializableBiPredicate<T, U> extends BiPredicate<T, U>, Serializable {}
+
   /**
    * Constructs a simple filter based on a predicate on OSH entities.
    *
@@ -23,7 +30,7 @@ public interface Filter extends FilterExpression {
    * @param oshCallback predicate which tests osh entities
    * @return a filter object which filters using the given predicate
    */
-  static Filter byOSHEntity(Predicate<OSHEntity> oshCallback) {
+  static Filter byOSHEntity(SerializablePredicate<OSHEntity> oshCallback) {
     return by(oshCallback, ignored -> true);
   }
 
@@ -38,7 +45,7 @@ static Filter byOSHEntity(Predicate<OSHEntity> oshCallback) {
    * @param osmCallback predicate which tests osm entities
    * @return a filter object which filters using the given predicate
    */
-  static Filter byOSMEntity(Predicate<OSMEntity> osmCallback) {
+  static Filter byOSMEntity(SerializablePredicate<OSMEntity> osmCallback) {
     return new NegatableFilter(osmCallback::test);
   }
 
@@ -54,7 +61,9 @@ static Filter byOSMEntity(Predicate<OSMEntity> osmCallback) {
    * @param osmCallback predicate which tests osm entities
    * @return a filter object which filters using the given predicates
    */
-  static Filter by(Predicate<OSHEntity> oshCallback, Predicate<OSMEntity> osmCallback) {
+  static Filter by(
+      SerializablePredicate<OSHEntity> oshCallback,
+      SerializablePredicate<OSMEntity> osmCallback) {
     return by(oshCallback, osmCallback, (ignored, ignored2) -> true);
   }
 
@@ -75,9 +84,9 @@ static Filter by(Predicate<OSHEntity> oshCallback, Predicate<OSMEntity> osmCallb
    * @return a filter object which filters using the given predicates
    */
   static Filter by(
-      Predicate<OSHEntity> oshCallback,
-      Predicate<OSMEntity> osmCallback,
-      BiPredicate<OSMEntity, Supplier<Geometry>> geomCallback
+      SerializablePredicate<OSHEntity> oshCallback,
+      SerializablePredicate<OSMEntity> osmCallback,
+      SerializableBiPredicate<OSMEntity, Supplier<Geometry>> geomCallback
   ) {
     return new NegatableFilter(new FilterInternal() {
       @Override