Stream results out of rest api.

nflow-engine/src/main/java/io/nflow/engine/internal/dao/WorkflowInstanceDao.java

@@ -53,7 +53,6 @@
 import org.springframework.jdbc.core.JdbcTemplate;
 import org.springframework.jdbc.core.PreparedStatementCreator;
 import org.springframework.jdbc.core.ResultSetExtractor;
-import org.springframework.jdbc.core.RowCallbackHandler;
 import org.springframework.jdbc.core.RowMapper;
 import org.springframework.jdbc.core.namedparam.MapSqlParameterSource;
 import org.springframework.jdbc.core.namedparam.NamedParameterJdbcTemplate;
@@ -522,12 +521,9 @@ private void fillState(final WorkflowInstance instance) {
     jdbc.query("select outside.state_key, outside.state_value from nflow_workflow_state outside inner join "
         + "(select workflow_id, max(action_id) action_id, state_key from nflow_workflow_state where workflow_id = ? group by workflow_id, state_key) inside "
         + "on outside.workflow_id = inside.workflow_id and outside.action_id = inside.action_id and outside.state_key = inside.state_key",
-        new RowCallbackHandler() {
-          @Override
-          public void processRow(ResultSet rs) throws SQLException {
-            instance.stateVariables.put(rs.getString(1), rs.getString(2));
-          }
-        }, instance.id);
+            rs -> {
+              instance.stateVariables.put(rs.getString(1), rs.getString(2));
+            }, instance.id);
     instance.originalStateVariables.putAll(instance.stateVariables);
   }
 
@@ -623,6 +619,10 @@ public int compareTo(OptimisticLockKey other) {
   }
 
   public List<WorkflowInstance> queryWorkflowInstances(QueryWorkflowInstances query) {
+    return queryWorkflowInstancesAsStream(query).collect(toList());
+  }
+
+  public Stream<WorkflowInstance> queryWorkflowInstancesAsStream(QueryWorkflowInstances query) {
     String sql = "select * from nflow_workflow ";
     List<String> conditions = new ArrayList<>();
     MapSqlParameterSource params = new MapSqlParameterSource();
@@ -664,43 +664,35 @@ public List<WorkflowInstance> queryWorkflowInstances(QueryWorkflowInstances quer
     params.addValue("executor_group", executorInfo.getExecutorGroup());
     sql += " where " + collectionToDelimitedString(conditions, " and ") + " order by id desc";
     sql = sqlVariants.limit(sql, getMaxResults(query.maxResults));
-    List<WorkflowInstance> ret = namedJdbc.query(sql, params, new WorkflowInstanceRowMapper()).stream()
-        .map(WorkflowInstance.Builder::build).collect(toList());
+
+    Stream<WorkflowInstance> ret = namedJdbc.query(sql, params, new WorkflowInstanceRowMapper()).stream()
+            .map(WorkflowInstance.Builder::build);
     if (query.includeCurrentStateVariables) {
-      for (WorkflowInstance instance : ret) {
-        fillState(instance);
-      }
+      ret = ret.peek(instance -> fillState(instance));
     }
     if (query.includeActions) {
-      for (WorkflowInstance instance : ret) {
-        fillActions(instance, query.includeActionStateVariables, query.maxActions);
-      }
+      ret = ret.peek(instance -> fillActions(instance, query.includeActionStateVariables, query.maxActions));
     }
     if (query.includeChildWorkflows) {
-      for (final WorkflowInstance instance : ret) {
-        fillChildWorkflowIds(instance);
-      }
+      ret = ret.peek(instance -> fillChildWorkflowIds(instance));
     }
     return ret;
   }
 
   private void fillChildWorkflowIds(final WorkflowInstance instance) {
-    jdbc.query("select parent_action_id, id from nflow_workflow where parent_workflow_id = ?", new RowCallbackHandler() {
-      @Override
-      public void processRow(ResultSet rs) throws SQLException {
-        long parentActionId = rs.getLong(1);
-        long childWorkflowInstanceId = rs.getLong(2);
-        List<Long> children = instance.childWorkflows.computeIfAbsent(parentActionId, k -> new ArrayList<>());
-        children.add(childWorkflowInstanceId);
-      }
+    jdbc.query("select parent_action_id, id from nflow_workflow where parent_workflow_id = ?", rs -> {
+      long parentActionId = rs.getLong(1);
+      long childWorkflowInstanceId = rs.getLong(2);
+      List<Long> children = instance.childWorkflows.computeIfAbsent(parentActionId, k -> new ArrayList<>());
+      children.add(childWorkflowInstanceId);
     }, instance.id);
   }
 
   private long getMaxResults(Long maxResults) {
     if (maxResults == null) {
       return workflowInstanceQueryMaxResultsDefault;
     }
-    return min(maxResults.longValue(), workflowInstanceQueryMaxResults);
+    return min(maxResults, workflowInstanceQueryMaxResults);
   }
 
   private void fillActions(WorkflowInstance instance, boolean includeStateVariables, Long maxActions) {
@@ -716,7 +708,7 @@ private long getMaxActions(Long maxActions) {
     if (maxActions == null) {
       return workflowInstanceQueryMaxActionsDefault;
     }
-    return min(maxActions.longValue(), workflowInstanceQueryMaxActions);
+    return min(maxActions, workflowInstanceQueryMaxActions);
   }
 
   private Map<Long, Map<String, String>> fetchActionStateVariables(WorkflowInstance instance) {

nflow-engine/src/main/java/io/nflow/engine/service/WorkflowInstanceService.java

@@ -7,10 +7,12 @@
 import java.util.List;
 import java.util.Optional;
 import java.util.Set;
+import java.util.stream.Stream;
 
 import javax.inject.Inject;
 
 import org.slf4j.Logger;
+import org.springframework.dao.EmptyResultDataAccessException;
 import org.springframework.stereotype.Component;
 import org.springframework.transaction.annotation.Transactional;
 import org.springframework.util.Assert;
@@ -49,7 +51,8 @@ public WorkflowInstanceService(WorkflowInstanceDao workflowInstanceDao, Workflow
    * @param id Workflow instance id.
    * @param includes Set of properties to be loaded.
    * @param maxActions Maximum number of actions to be loaded.
-   * @return The workflow instance, or null if not found.
+   * @return The workflow instance.
+   * @throws EmptyResultDataAccessException If workflow instance is not found.
    */
   public WorkflowInstance getWorkflowInstance(long id, Set<WorkflowInstanceInclude> includes, Long maxActions) {
     return workflowInstanceDao.getWorkflowInstance(id, includes, maxActions);
@@ -126,6 +129,15 @@ public Collection<WorkflowInstance> listWorkflowInstances(QueryWorkflowInstances
     return workflowInstanceDao.queryWorkflowInstances(query);
   }
 
+  /**
+   * Return workflow instances matching the given query.
+   * @param query The query parameters.
+   * @return Matching workflow instances as Stream. The stream does not need to be closed.
+   */
+  public Stream<WorkflowInstance> listWorkflowInstancesAsStream(QueryWorkflowInstances query) {
+    return workflowInstanceDao.queryWorkflowInstancesAsStream(query);
+  }
+
   /**
    * Return current signal value for given workflow instance.
    * @param workflowInstanceId Workflow instance id.

nflow-engine/src/test/java/io/nflow/engine/internal/dao/WorkflowInstanceDaoTest.java

@@ -56,6 +56,7 @@
 import org.junit.jupiter.api.Test;
 import org.mockito.ArgumentCaptor;
 import org.springframework.core.env.Environment;
+import org.springframework.dao.EmptyResultDataAccessException;
 import org.springframework.jdbc.core.JdbcTemplate;
 import org.springframework.jdbc.core.RowCallbackHandler;
 import org.springframework.jdbc.core.namedparam.NamedParameterJdbcTemplate;
@@ -106,6 +107,13 @@ public void roundTripTest() {
     checkSameWorkflowInfo(i1, i2);
   }
 
+  @Test
+  public void queryNonExistingWorkflowThrowsException() {
+    assertThrows(EmptyResultDataAccessException.class, () ->
+      dao.getWorkflowInstance(-42, emptySet(), null)
+    );
+  }
+
   @Test
   public void queryWorkflowInstanceWithAllConditions() {
     WorkflowInstance i1 = constructWorkflowInstanceBuilder().build();

nflow-rest-api-common/src/main/java/io/nflow/rest/v1/ResourceBase.java

@@ -130,7 +130,7 @@ public boolean updateWorkflowInstance(final long id,
     return workflowInstances.updateWorkflowInstance(instance, action);
   }
 
-  public Collection<ListWorkflowInstanceResponse> listWorkflowInstances(final List<Long> ids, final List<String> types,
+  public Stream<ListWorkflowInstanceResponse> listWorkflowInstances(final List<Long> ids, final List<String> types,
       final Long parentWorkflowId, final Long parentActionId, final List<String> states,
       final List<WorkflowInstanceStatus> statuses, final String businessKey, final String externalId, final String include,
       final Long maxResults, final Long maxActions, final WorkflowInstanceService workflowInstances,
@@ -151,13 +151,9 @@ public Collection<ListWorkflowInstanceResponse> listWorkflowInstances(final List
         .setMaxResults(maxResults) //
         .setMaxActions(maxActions) //
         .setIncludeChildWorkflows(includeStrings.contains(childWorkflows)).build();
-    Collection<WorkflowInstance> instances = workflowInstances.listWorkflowInstances(q);
-    List<ListWorkflowInstanceResponse> resp = new ArrayList<>();
+    Stream<WorkflowInstance> instances = workflowInstances.listWorkflowInstancesAsStream(q);
     Set<WorkflowInstanceInclude> parseIncludeEnums = parseIncludeEnums(include);
-    for (WorkflowInstance instance : instances) {
-      resp.add(listWorkflowConverter.convert(instance, parseIncludeEnums));
-    }
-    return resp;
+    return instances.map(instance -> listWorkflowConverter.convert(instance, parseIncludeEnums));
   }
 
   private Set<WorkflowInstanceInclude> parseIncludeEnums(String include) {

nflow-rest-api-jax-rs/src/main/java/io/nflow/rest/v1/jaxrs/WorkflowInstanceResource.java

@@ -12,9 +12,9 @@
 import static javax.ws.rs.core.Response.Status.CONFLICT;
 
 import java.net.URI;
-import java.util.Collection;
 import java.util.Collections;
 import java.util.EnumSet;
+import java.util.Iterator;
 import java.util.List;
 
 import javax.inject.Inject;
@@ -129,7 +129,7 @@ public ListWorkflowInstanceResponse fetchWorkflowInstance(
 
   @GET
   @ApiOperation(value = "List workflow instances", response = ListWorkflowInstanceResponse.class, responseContainer = "List")
-  public Collection<ListWorkflowInstanceResponse> listWorkflowInstances(
+  public Iterator<ListWorkflowInstanceResponse> listWorkflowInstances(
       @QueryParam("id") @ApiParam("Internal id of workflow instance") List<Long> ids,
       @QueryParam("type") @ApiParam("Workflow definition type of workflow instance") List<String> types,
       @QueryParam("parentWorkflowId") @ApiParam("Id of parent workflow instance") Long parentWorkflowId,
@@ -143,7 +143,7 @@ public Collection<ListWorkflowInstanceResponse> listWorkflowInstances(
       @QueryParam("maxActions") @ApiParam("Maximum number of actions returned for each workflow instance") Long maxActions) {
     return super.listWorkflowInstances(ids, types, parentWorkflowId, parentActionId, states,
         statuses, businessKey, externalId, include, maxResults, maxActions,
-        workflowInstances, listWorkflowConverter);
+        workflowInstances, listWorkflowConverter).iterator();
   }
 
   @PUT

nflow-rest-api-jax-rs/src/test/java/io/nflow/rest/v1/jaxrs/WorkflowInstanceResourceTest.java

@@ -182,7 +182,7 @@ public void whenUpdatingStateVariablesUpdateWorkflowInstanceWorks() {
   public void listWorkflowInstancesWorks() {
     resource.listWorkflowInstances(asList(42L), asList("type"), 99L, 88L, asList("state"),
         asList(WorkflowInstanceStatus.created), "businessKey", "externalId", "", null, null);
-    verify(workflowInstances).listWorkflowInstances((QueryWorkflowInstances) argThat(allOf(
+    verify(workflowInstances).listWorkflowInstancesAsStream((QueryWorkflowInstances) argThat(allOf(
         hasField("ids", contains(42L)),
         hasField("types", contains("type")),
         hasField("parentWorkflowId", is(99L)),
@@ -204,7 +204,7 @@ public void listWorkflowInstancesWorksWithAllIncludes() {
     resource.listWorkflowInstances(asList(42L), asList("type"), 99L, 88L, asList("state"),
         asList(WorkflowInstanceStatus.created, WorkflowInstanceStatus.executing),
         "businessKey", "externalId", "actions,currentStateVariables,actionStateVariables,childWorkflows", 1L, 1L);
-    verify(workflowInstances).listWorkflowInstances((QueryWorkflowInstances) argThat(allOf(
+    verify(workflowInstances).listWorkflowInstancesAsStream((QueryWorkflowInstances) argThat(allOf(
         hasField("ids", contains(42L)),
         hasField("types", contains("type")),
         hasField("parentWorkflowId", is(99L)),

nflow-rest-api-spring-web/src/main/java/io/nflow/rest/v1/springweb/WorkflowInstanceResource.java

@@ -12,9 +12,9 @@
 import static org.springframework.http.ResponseEntity.status;
 
 import java.net.URI;
-import java.util.Collection;
 import java.util.Collections;
 import java.util.EnumSet;
+import java.util.Iterator;
 import java.util.List;
 
 import javax.inject.Inject;
@@ -115,7 +115,7 @@ public ResponseEntity<ListWorkflowInstanceResponse> fetchWorkflowInstance(
 
   @GetMapping
   @ApiOperation(value = "List workflow instances", response = ListWorkflowInstanceResponse.class, responseContainer = "List")
-  public Collection<ListWorkflowInstanceResponse> listWorkflowInstances(
+  public Iterator<ListWorkflowInstanceResponse> listWorkflowInstances(
       @RequestParam(value = "id", defaultValue = "") @ApiParam("Internal id of workflow instance") List<Long> ids,
       @RequestParam(value = "type", defaultValue = "") @ApiParam("Workflow definition type of workflow instance") List<String> types,
       @RequestParam(value = "parentWorkflowId", required = false) @ApiParam("Id of parent workflow instance") Long parentWorkflowId,
@@ -128,7 +128,7 @@ public Collection<ListWorkflowInstanceResponse> listWorkflowInstances(
       @RequestParam(value = "maxResults", required = false) @ApiParam("Maximum number of workflow instances to be returned") Long maxResults,
       @RequestParam(value = "maxActions", required = false) @ApiParam("Maximum number of actions returned for each workflow instance") Long maxActions) {
     return super.listWorkflowInstances(ids, types, parentWorkflowId, parentActionId, states, statuses, businessKey, externalId,
-        include, maxResults, maxActions, this.workflowInstances, this.listWorkflowConverter);
+        include, maxResults, maxActions, this.workflowInstances, this.listWorkflowConverter).iterator();
   }
 
   @PutMapping(path = "/{id}/signal", consumes = APPLICATION_JSON_VALUE)