Avoid NPE on MyBatisCursorItemReader

Fixes gh-237

Author: kazuki43zoo

src/main/java/org/mybatis/spring/batch/MyBatisCursorItemReader.java

@@ -71,8 +71,12 @@ protected void doOpen() throws Exception {
 
   @Override
   protected void doClose() throws Exception {
-    cursor.close();
-    sqlSession.close();
+    if (cursor != null) {
+      cursor.close();
+    }
+    if (sqlSession != null) {
+      sqlSession.close();
+    }
     cursorIterator = null;
   }
 

src/test/java/org/mybatis/spring/batch/MyBatisCursorItemReaderTest.java

@@ -0,0 +1,104 @@
+/**
+ *    Copyright 2010-2017 the original author or authors.
+ *
+ *    Licensed under the Apache License, Version 2.0 (the "License");
+ *    you may not use this file except in compliance with the License.
+ *    You may obtain a copy of the License at
+ *
+ *       http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *    Unless required by applicable law or agreed to in writing, software
+ *    distributed under the License is distributed on an "AS IS" BASIS,
+ *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *    See the License for the specific language governing permissions and
+ *    limitations under the License.
+ */
+package org.mybatis.spring.batch;
+
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.List;
+
+import org.apache.ibatis.cursor.Cursor;
+import org.apache.ibatis.session.ExecutorType;
+import org.apache.ibatis.session.SqlSession;
+import org.apache.ibatis.session.SqlSessionFactory;
+import org.assertj.core.api.Assertions;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.mockito.Mock;
+import org.mockito.Mockito;
+import org.mockito.MockitoAnnotations;
+import org.springframework.batch.item.ExecutionContext;
+import org.springframework.batch.item.ItemStreamException;
+
+/**
+ * Tests for {@link MyBatisCursorItemReader}.
+ */
+class MyBatisCursorItemReaderTest {
+
+  @Mock
+  private SqlSessionFactory sqlSessionFactory;
+
+  @Mock
+  private SqlSession sqlSession;
+
+  @Mock
+  private Cursor<Object> cursor;
+
+  @BeforeEach
+  void setUp() {
+    MockitoAnnotations.initMocks(this);
+  }
+
+  @Test
+  void testCloseOnFailing() throws Exception {
+
+    Mockito.when(this.sqlSessionFactory.openSession(ExecutorType.SIMPLE))
+        .thenReturn(this.sqlSession);
+    Mockito.when(this.cursor.iterator()).thenReturn(getFoos().iterator());
+    Mockito.when(this.sqlSession.selectCursor("selectFoo", Collections.singletonMap("id", 1)))
+        .thenThrow(new RuntimeException("error."));
+
+    MyBatisCursorItemReader<Foo> itemReader = new MyBatisCursorItemReader<>();
+    itemReader.setSqlSessionFactory(this.sqlSessionFactory);
+    itemReader.setQueryId("selectFoo");
+    itemReader.setParameterValues(Collections.singletonMap("id", 1));
+    itemReader.afterPropertiesSet();
+
+    ExecutionContext executionContext = new ExecutionContext();
+    try {
+      itemReader.open(executionContext);
+    } catch (ItemStreamException e) {
+      Assertions.assertThat(e).hasMessage("Failed to initialize the reader")
+          .hasCause(new RuntimeException("error."));
+    } finally {
+      itemReader.close();
+      Mockito.verify(this.sqlSession).close();
+    }
+
+  }
+
+  @Test
+  void testCloseBeforeOpen() {
+    MyBatisCursorItemReader<Foo> itemReader = new MyBatisCursorItemReader<>();
+    itemReader.close();
+  }
+
+  private List<Object> getFoos() {
+    return Arrays.asList(new Foo("foo1"), new Foo("foo2"), new Foo("foo3"));
+  }
+
+  private static class Foo {
+    private final String name;
+
+    public Foo(String name) {
+      this.name = name;
+    }
+
+    public String getName() {
+      return this.name;
+    }
+  }
+
+}