我的Kafka主题有这种格式的消息

user1,subject1,80|user1,subject2,90 

user2,subject1,70|user2,subject2,100 

and so on.

我已经创建了如下用户pojo。

class User implements Serializable{
/**
 * 
 */
private static final long serialVersionUID = -253687203767610477L;
private String userId;
private String subject;
private String marks;

public User(String userId, String subject, String marks) {
    super();
    this.userId = userId;
    this.subject = subject;
    this.marks = marks;
}

public String getUserId() {
    return userId;
}

public void setUserId(String userId) {
    this.userId = userId;
}
public String getSubject() {
    return subject;
}
public void setSubject(String subject) {
    this.subject = subject;
}
public String getMarks() {
    return marks;
}
public void setMarks(String marks) {
    this.marks = marks;
}
}

此外，我还创建了默认键值序列化

streamProperties.put(
            StreamsConfig.DEFAULT_KEY_SERDE_CLASS_CONFIG, Serdes.String().getClass());
streamProperties.put(
            StreamsConfig.DEFAULT_VALUE_SERDE_CLASS_CONFIG, Serdes.String().getClass());

我试图通过userid找到count，如下所示。我还需要用户对象来执行一些其他功能。

KTable<String, Long> wordCount = streamInput

    .flatMap(new KeyValueMapper<String, String, Iterable<KeyValue<String,User>>>() {

        @Override
        public Iterable<KeyValue<String, User>> apply(String key, String value) {
            String[] userObjects = value.split("|");
            List<KeyValue<String, User>> userList = new LinkedList<>();
            for(String userObject: userObjects) {
                String[] userData = userObject.split(",");
                userList.add(KeyValue.pair(userData[0],
                        new User(userData[0],userData[1],userData[2])));

            }
            return userList;
        }
    })

.groupByKey()
.count();

我得到下面的错误

Caused by: org.apache.kafka.streams.errors.StreamsException: A serializer (key: org.apache.kafka.common.serialization.StringSerializer / value: org.apache.kafka.common.serialization.StringSerializer) is not compatible to the actual key or value type (key type: java.lang.String / value type: com.example.testing.dao.User). Change the default Serdes in StreamConfig or provide correct Serdes via method parameters.

我想我需要提供正确的答案 Serde 对于用户类。