[SPARK-19666][SQL] Skip a property without getter in Java schema inference and allow empty bean in encoder creation

## What changes were proposed in this pull request?

This PR proposes to fix two.

**Skip a property without a getter in beans**

Currently, if we use a JavaBean without the getter as below:

```java
public static class BeanWithoutGetter implements Serializable {
  private String a;

  public void setA(String a) {
    this.a = a;
  }
}

BeanWithoutGetter bean = new BeanWithoutGetter();
List<BeanWithoutGetter> data = Arrays.asList(bean);
spark.createDataFrame(data, BeanWithoutGetter.class).show();
```

- Before

It throws an exception as below:

```
java.lang.NullPointerException
	at org.spark_project.guava.reflect.TypeToken.method(TypeToken.java:465)
	at org.apache.spark.sql.catalyst.JavaTypeInference$$anonfun$2.apply(JavaTypeInference.scala:126)
	at org.apache.spark.sql.catalyst.JavaTypeInference$$anonfun$2.apply(JavaTypeInference.scala:125)
```

- After

```
++
||
++
||
++
```

**Supports empty bean in encoder creation**

```java
public static class EmptyBean implements Serializable {}

EmptyBean bean = new EmptyBean();
List<EmptyBean> data = Arrays.asList(bean);
spark.createDataset(data, Encoders.bean(EmptyBean.class)).show();
```

- Before

throws an exception as below:

```
java.lang.UnsupportedOperationException: Cannot infer type for class EmptyBean because it is not bean-compliant
	at org.apache.spark.sql.catalyst.JavaTypeInference$.org$apache$spark$sql$catalyst$JavaTypeInference$$serializerFor(JavaTypeInference.scala:436)
	at org.apache.spark.sql.catalyst.JavaTypeInference$.serializerFor(JavaTypeInference.scala:341)
```

- After

```
++
||
++
||
++
```

## How was this patch tested?

Unit test in `JavaDataFrameSuite`.

Author: hyukjinkwon <gurwls223@gmail.com>

Closes #17013 from HyukjinKwon/SPARK-19666.

2 files changed, 28 insertions, 0 deletions

diff --git a/sql/core/src/test/java/test/org/apache/spark/sql/JavaDataFrameSuite.java b/sql/core/src/test/java/test/org/apache/spark/sql/JavaDataFrameSuite.java
index c3b94a44c2..a8f814bfae 100644
--- a/sql/core/src/test/java/test/org/apache/spark/sql/JavaDataFrameSuite.java
+++ b/sql/core/src/test/java/test/org/apache/spark/sql/JavaDataFrameSuite.java
@@ -397,4 +397,21 @@ public class JavaDataFrameSuite {
       Assert.assertTrue(filter4.mightContain(i * 3));
     }
   }
+
+  public static class BeanWithoutGetter implements Serializable {
+    private String a;
+
+    public void setA(String a) {
+      this.a = a;
+    }
+  }
+
+  @Test
+  public void testBeanWithoutGetter() {
+    BeanWithoutGetter bean = new BeanWithoutGetter();
+    List<BeanWithoutGetter> data = Arrays.asList(bean);
+    Dataset<Row> df = spark.createDataFrame(data, BeanWithoutGetter.class);
+    Assert.assertEquals(df.schema().length(), 0);
+    Assert.assertEquals(df.collectAsList().size(), 1);
+  }
 }
diff --git a/sql/core/src/test/java/test/org/apache/spark/sql/JavaDatasetSuite.java b/sql/core/src/test/java/test/org/apache/spark/sql/JavaDatasetSuite.java
index 577672ca8e..4581c6ebe9 100644
--- a/sql/core/src/test/java/test/org/apache/spark/sql/JavaDatasetSuite.java
+++ b/sql/core/src/test/java/test/org/apache/spark/sql/JavaDatasetSuite.java
@@ -1276,4 +1276,15 @@ public class JavaDatasetSuite implements Serializable {
       spark.createDataset(data, Encoders.bean(NestedComplicatedJavaBean.class));
     ds.collectAsList();
   }
+
+  public static class EmptyBean implements Serializable {}
+
+  @Test
+  public void testEmptyBean() {
+    EmptyBean bean = new EmptyBean();
+    List<EmptyBean> data = Arrays.asList(bean);
+    Dataset<EmptyBean> df = spark.createDataset(data, Encoders.bean(EmptyBean.class));
+    Assert.assertEquals(df.schema().length(), 0);
+    Assert.assertEquals(df.collectAsList().size(), 1);
+  }
 }