Json mapper (#258)

* Implemented Pojo mapper using jackson
Added other exception kinds

Signed-off-by: Francesco Guardiani <francescoguard@gmail.com>

* Fixup for the rebase

Signed-off-by: Francesco Guardiani <francescoguard@gmail.com>

* Removed comment

Signed-off-by: Francesco Guardiani <francescoguard@gmail.com>

* Equals and hash code

Signed-off-by: Francesco Guardiani <francescoguard@gmail.com>

* Fixed rebase issues

Signed-off-by: Francesco Guardiani <francescoguard@gmail.com>

api/src/main/java/io/cloudevents/rw/CloudEventRWException.java

@@ -25,6 +25,7 @@ public class CloudEventRWException extends RuntimeException {
         INVALID_ATTRIBUTE_TYPE,
         INVALID_ATTRIBUTE_VALUE,
         INVALID_EXTENSION_TYPE,
+        DATA_CONVERSION,
         OTHER
     }
 
@@ -85,6 +86,14 @@ public class CloudEventRWException extends RuntimeException {
         );
     }
 
+    public static CloudEventRWException newDataConversion(Throwable cause, String to) {
+        return new CloudEventRWException(
+            CloudEventRWExceptionKind.DATA_CONVERSION,
+            "Error while trying to convert data to " + to,
+            cause
+        );
+    }
+
     public static CloudEventRWException newOther(Throwable cause) {
         return new CloudEventRWException(
             CloudEventRWExceptionKind.OTHER,

formats/json-jackson/src/main/java/io/cloudevents/jackson/PojoCloudEventData.java

@@ -0,0 +1,54 @@
+package io.cloudevents.jackson;
+
+import com.fasterxml.jackson.core.JsonProcessingException;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import io.cloudevents.CloudEventData;
+import io.cloudevents.rw.CloudEventRWException;
+
+import java.util.Objects;
+
+public class PojoCloudEventData<T> implements CloudEventData {
+
+    private final ObjectMapper mapper;
+    private byte[] memoizedValue;
+    private final T value;
+
+    protected PojoCloudEventData(ObjectMapper mapper, T value) {
+        this(mapper, value, null);
+    }
+
+    protected PojoCloudEventData(ObjectMapper mapper, T value, byte[] memoizedValue) {
+        this.mapper = mapper;
+        this.value = value;
+        this.memoizedValue = memoizedValue;
+    }
+
+    public T getValue() {
+        return value;
+    }
+
+    @Override
+    public byte[] toBytes() {
+        if (this.memoizedValue == null) {
+            try {
+                this.memoizedValue = mapper.writeValueAsBytes(value);
+            } catch (JsonProcessingException e) {
+                throw CloudEventRWException.newDataConversion(e, "byte[]");
+            }
+        }
+        return this.memoizedValue;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) return true;
+        if (o == null || getClass() != o.getClass()) return false;
+        PojoCloudEventData<?> that = (PojoCloudEventData<?>) o;
+        return Objects.equals(getValue(), that.getValue());
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(getValue());
+    }
+}

formats/json-jackson/src/main/java/io/cloudevents/jackson/PojoCloudEventDataMapper.java

@@ -0,0 +1,48 @@
+package io.cloudevents.jackson;
+
+import com.fasterxml.jackson.core.type.TypeReference;
+import com.fasterxml.jackson.databind.JsonNode;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import io.cloudevents.CloudEventData;
+import io.cloudevents.rw.CloudEventDataMapper;
+import io.cloudevents.rw.CloudEventRWException;
+
+public class PojoCloudEventDataMapper<T> implements CloudEventDataMapper<PojoCloudEventData<T>> {
+
+    private final ObjectMapper mapper;
+    private final TypeReference<T> target;
+
+    private PojoCloudEventDataMapper(ObjectMapper mapper, TypeReference<T> target) {
+        this.mapper = mapper;
+        this.target = target;
+    }
+
+    @Override
+    public PojoCloudEventData<T> map(CloudEventData data) throws CloudEventRWException {
+        // Best case, event is already from json
+        if (data instanceof JsonCloudEventData) {
+            JsonNode node = ((JsonCloudEventData) data).getNode();
+            T value;
+            try {
+                value = this.mapper.convertValue(node, target);
+            } catch (Exception e) {
+                throw CloudEventRWException.newDataConversion(e, target.getType().toString());
+            }
+            return new PojoCloudEventData<>(mapper, value);
+        }
+
+        // Worst case, deserialize from bytes
+        T value;
+        byte[] bytes = data.toBytes();
+        try {
+            value = this.mapper.readValue(bytes, this.target);
+        } catch (Exception e) {
+            throw CloudEventRWException.newDataConversion(e, target.getType().toString());
+        }
+        return new PojoCloudEventData<>(mapper, value, bytes);
+    }
+
+    public static <T> PojoCloudEventDataMapper<T> from(ObjectMapper mapper, TypeReference<T> target) {
+        return new PojoCloudEventDataMapper<>(mapper, target);
+    }
+}

formats/json-jackson/src/test/java/io/cloudevents/jackson/MyPojo.java

@@ -0,0 +1,38 @@
+package io.cloudevents.jackson;
+
+import java.util.Objects;
+
+public class MyPojo {
+    public int a;
+    public String b;
+
+    public MyPojo() {
+    }
+
+    public MyPojo(int a, String b) {
+        this.a = a;
+        this.b = b;
+    }
+
+    public int getA() {
+        return a;
+    }
+
+    public void setA(int a) {
+        this.a = a;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) return true;
+        if (o == null || getClass() != o.getClass()) return false;
+        MyPojo myPojo = (MyPojo) o;
+        return getA() == myPojo.getA() &&
+            Objects.equals(b, myPojo.b);
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(getA(), b);
+    }
+}

formats/json-jackson/src/test/java/io/cloudevents/jackson/PojoCloudEventDataMapperTest.java

@@ -0,0 +1,59 @@
+package io.cloudevents.jackson;
+
+import com.fasterxml.jackson.core.type.TypeReference;
+import com.fasterxml.jackson.databind.JsonNode;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.node.JsonNodeFactory;
+import io.cloudevents.CloudEvent;
+import io.cloudevents.core.builder.CloudEventBuilder;
+import io.cloudevents.core.impl.CloudEventUtils;
+import io.cloudevents.core.test.Data;
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class PojoCloudEventDataMapperTest {
+
+    private final JsonNode myPojoJson = JsonNodeFactory.instance.objectNode().put("a", 10).put("b", "Hello World!");
+    private final String myPojoSerialized = myPojoJson.toString();
+    private final MyPojo myPojo = new MyPojo(10, "Hello World!");
+
+    @Test
+    public void testWithBytes() {
+        ObjectMapper objectMapper = new ObjectMapper();
+
+        CloudEvent event = CloudEventBuilder.v1(Data.V1_MIN)
+            .withData("application/json", myPojoSerialized.getBytes())
+            .build();
+
+        PojoCloudEventData<MyPojo> mappedData = CloudEventUtils.mapData(
+            event,
+            PojoCloudEventDataMapper.from(objectMapper, new TypeReference<MyPojo>() {
+            })
+        );
+        assertThat(mappedData)
+            .isNotNull()
+            .extracting(PojoCloudEventData::getValue)
+            .isEqualTo(myPojo);
+    }
+
+    @Test
+    public void testWithJson() {
+        ObjectMapper objectMapper = new ObjectMapper();
+
+        CloudEvent event = CloudEventBuilder.v1(Data.V1_MIN)
+            .withData("application/json", new JsonCloudEventData(myPojoJson))
+            .build();
+
+        PojoCloudEventData<MyPojo> mappedData = CloudEventUtils.mapData(
+            event,
+            PojoCloudEventDataMapper.from(objectMapper, new TypeReference<MyPojo>() {
+            })
+        );
+        assertThat(mappedData)
+            .isNotNull()
+            .extracting(PojoCloudEventData::getValue)
+            .isEqualTo(myPojo);
+    }
+
+}