org.springframework.data.redis.serializer.SerializationException: Cannot serialize;

    org.springframework.data.redis.serializer.SerializationException: Cannot serialize; nested exception is                 org.springframework.core.serializer.support.SerializationFailedException: Failed to serialize object using DefaultSerializer; nested         exception is java.io.NotSerializableException: com.ssm.promotion.core.entity.Article

    at org.springframework.data.redis.serializer.JdkSerializationRedisSerializer.serialize(JdkSerializationRedisSerializer.java:92)
    at org.springframework.data.redis.cache.RedisCache$CacheValueAccessor.convertToBytesIfNecessary(RedisCache.java:375)
    at org.springframework.data.redis.cache.RedisCache$BinaryRedisCacheElement.<init>(RedisCache.java:408)
    at org.springframework.data.redis.cache.RedisCache.put(RedisCache.java:173)
    at org.springframework.data.redis.cache.RedisCache.put(RedisCache.java:157)
    at com.ssm.promotion.core.redis.RedisUtil.put(RedisUtil.java:31)
    at test.RedisTest.redisPutListArticleTest(RedisTest.java:77)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:44)
    at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:15)
    at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:41)
    at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:20)
    at org.springframework.test.context.junit4.statements.RunBeforeTestMethodCallbacks.evaluate(RunBeforeTestMethodCallbacks.java:75)
    at org.springframework.test.context.junit4.statements.RunAfterTestMethodCallbacks.evaluate(RunAfterTestMethodCallbacks.java:86)
    at org.springframework.test.context.junit4.statements.SpringRepeat.evaluate(SpringRepeat.java:84)
    at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:263)
    at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:254)
    at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:89)
    at org.junit.runners.ParentRunner$3.run(ParentRunner.java:231)
    at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:60)
    at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:229)
    at org.junit.runners.ParentRunner.access$000(ParentRunner.java:50)
    at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:222)
    at org.springframework.test.context.junit4.statements.RunBeforeTestClassCallbacks.evaluate(RunBeforeTestClassCallbacks.java:61)
    at org.springframework.test.context.junit4.statements.RunAfterTestClassCallbacks.evaluate(RunAfterTestClassCallbacks.java:70)
    at org.junit.runners.ParentRunner.run(ParentRunner.java:292)
    at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.run(SpringJUnit4ClassRunner.java:193)
    at org.junit.runner.JUnitCore.run(JUnitCore.java:157)
    at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:68)
    at com.intellij.rt.execution.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:47)
    at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:242)
    at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:70)
Caused by: org.springframework.core.serializer.support.SerializationFailedException: Failed to serialize object using DefaultSerializer; nested exception is java.io.NotSerializableException: com.ssm.promotion.core.entity.Article
    at org.springframework.core.serializer.support.SerializingConverter.convert(SerializingConverter.java:68)
    at org.springframework.core.serializer.support.SerializingConverter.convert(SerializingConverter.java:35)
    at org.springframework.data.redis.serializer.JdkSerializationRedisSerializer.serialize(JdkSerializationRedisSerializer.java:90)
    ... 34 more
Caused by: java.io.NotSerializableException: com.ssm.promotion.core.entity.Article
    at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1184)
    at java.io.ObjectOutputStream.writeObject(ObjectOutputStream.java:348)
    at java.util.ArrayList.writeObject(ArrayList.java:762)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at java.io.ObjectStreamClass.invokeWriteObject(ObjectStreamClass.java:1028)
    at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1496)
    at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1432)
    at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1178)
    at java.io.ObjectOutputStream.writeObject(ObjectOutputStream.java:348)
    at org.springframework.core.serializer.DefaultSerializer.serialize(DefaultSerializer.java:46)
    at org.springframework.core.serializer.support.SerializingConverter.convert(SerializingConverter.java:63)
    ... 36 more

Caused by: java.io.NotSerializableException: com.ssm.promotion.core.entity.Article

public class Article implements Serializable