#1848 - ENH: Add EmptyPagedList ... as helper implementation of PagedList<T>

src/main/java/io/ebean/EmptyPagedList.java

@@ -0,0 +1,74 @@
+package io.ebean;
+
+import javax.annotation.Nonnull;
+import java.util.Collections;
+import java.util.List;
+import java.util.concurrent.Future;
+
+/**
+ * An empty PagedList.
+ * <p>
+ * For use in application code when we need to return a PagedList but don't want to
+ * execute a query.
+ * </p>
+ *
+ * <pre>{@code
+ *
+ *   PagedList<Customer> empty = PagedList.emptyList();
+ *
+ * }</pre>
+ */
+public class EmptyPagedList<T> implements PagedList<T> {
+
+  @Override
+  public void loadCount() {
+    // do nothing
+  }
+
+  @Nonnull
+  @Override
+  public Future<Integer> getFutureCount() {
+    return null;
+  }
+
+  @Nonnull
+  @Override
+  public List<T> getList() {
+    return Collections.emptyList();
+  }
+
+  @Override
+  public int getTotalCount() {
+    return 0;
+  }
+
+  @Override
+  public int getTotalPageCount() {
+    return 0;
+  }
+
+  @Override
+  public int getPageSize() {
+    return 0;
+  }
+
+  @Override
+  public int getPageIndex() {
+    return 0;
+  }
+
+  @Override
+  public boolean hasNext() {
+    return false;
+  }
+
+  @Override
+  public boolean hasPrev() {
+    return false;
+  }
+
+  @Override
+  public String getDisplayXtoYofZ(String to, String of) {
+    return "";
+  }
+}

src/main/java/io/ebean/PagedList.java

@@ -60,6 +60,13 @@ import java.util.concurrent.Future;
  */
 public interface PagedList<T> {
 
+  /**
+   * Return an empty PagedList.
+   */
+  static <B> PagedList<B> emptyList() {
+    return new EmptyPagedList<>();
+  }
+
   /**
    * Initiate the loading of the total row count in the background.
    * <pre>{@code

src/test/java/org/tests/query/TestQueryFindPagedList.java

@@ -5,6 +5,7 @@ import io.ebean.Ebean;
 import io.ebean.PagedList;
 import org.ebeantest.LoggedSqlCollector;
 import org.junit.Test;
+import org.tests.model.basic.Customer;
 import org.tests.model.basic.Order;
 import org.tests.model.basic.ResetBasicData;
 
@@ -22,6 +23,19 @@ import static org.junit.Assert.assertTrue;
 
 public class TestQueryFindPagedList extends BaseTestCase {
 
+  @Test
+  public void empty() {
+    PagedList<Customer> empty = PagedList.emptyList();
+
+    assertThat(empty.getList()).isEmpty();
+    assertThat(empty.getTotalPageCount()).isEqualTo(0);
+    assertThat(empty.getTotalCount()).isEqualTo(0);
+    assertThat(empty.getPageIndex()).isEqualTo(0);
+    assertThat(empty.getPageSize()).isEqualTo(0);
+    assertThat(empty.hasNext()).isFalse();
+    assertThat(empty.hasPrev()).isFalse();
+    assertThat(empty.getDisplayXtoYofZ("a", "b")).isEqualTo("");
+  }
 
   @Test(expected = PersistenceException.class)
   public void test_noMaxRows() throws ExecutionException, InterruptedException {