问题描述
我在 Apache Flink Statefun 3.0（自定义 Greeter 示例）中有一个 embedded 模块，它使用 JSON 序列化事件。当尝试从入口反序列化 route() 消息时，我收到一个异常，即我的自定义类型无法转换为 protobuf（是的，它不是）——但是应该吗？我的意思是我尝试使用 3.x 文档，但没有发现有关要路由的类型的任何限制。
对此有任何提示或指示吗？
谢谢
// The custom type (Bean-style and all)
public final class Message {
@JsonProperty private String name;
@JsonProperty private String id;
@JsonProperty private int visits;
public Message() {}
public String getName() { return name; }
public void setName(String s) { name = s; }
public String getId() { return id; }
public void setId(String s) { id = s; }
public int getVisits() { return visits; }
public void setVisits(int i) { visits = i; }
}
// The function
public class GreeterFn implements StatefulFunction {
public static final FunctionType TYPE = new FunctionType("example","greeter");
@Override
public void invoke(Context ctx,Object msg) {
// I never get here
}
}
// The module
public class EmbeddedModule implements StatefulFunctionModule {
static final IngressIdentifier<Message> INGRESS = new IngressIdentifier<>(Message.class,"example","names");
private static final class MsgDeser implements KafkaIngressDeserializer<Message> {
private final ObjectMapper mapper = new ObjectMapper();
@Override
public Message deserialize(ConsumerRecord<byte[],byte[]> input) {
try { return mapper.readValue(new String(input.value(),StandardCharsets.UTF_8),Message.class); }
catch (java.io.IOException e) { e.printstacktrace(); }
return null;
}
}
public void configure(Map<String,String> globalConfiguration,Binder binder) {
binder.bindIngress(KafkaIngressBuilder.forIdentifier(INGRESS)
.withKafkaAddress("kafka:9092")
.withTopic("names")
.withDeserializer(MsgDeser.class)
.withConsumerGroupId("my-group-id")
.build());
binder.bindIngressRouter(INGRESS,new Router<Message>() {
@Override
public void route(Message m,Downstream<Message> ds) {
ds.forward(GreeterFn.TYPE,m.getName(),m); // <-- I get here OK but then the exception
}
});
binder.bindFunctionProvider(GreeterFn.TYPE,x -> new GreeterFn());
}
}
// And the logs (trimmed)
statefun-worker_1 | 2021-07-12 11:29:33,366 WARN org.apache.flink.runtime.taskmanager.Task [] - Source: example-names-ingress -> router (names) (1/1)#0 (2b43e45ce4bcc61340ff131d147f3afe) switched from RUNNING to Failed.
statefun-worker_1 | java.lang.RuntimeException: class com.my.flink.Message cannot be cast to class com.google.protobuf.Message (com.my.flink.Message is in unnamed module of loader org.apache.flink.util.ChildFirstClassLoader @2aab3c1e; com.google.protobuf.Message is in unnamed module of loader 'app')
statefun-worker_1 | at org.apache.flink.streaming.runtime.io.RecordWriterOutput.pushToRecordWriter(RecordWriterOutput.java:103) ~[flink-dist_2.12-1.12.1.jar:1.12.1]
statefun-worker_1 | at org.apache.flink.streaming.runtime.io.RecordWriterOutput.collect(RecordWriterOutput.java:87) ~[flink-dist_2.12-1.12.1.jar:1.12.1]
statefun-worker_1 | at org.apache.flink.streaming.runtime.io.RecordWriterOutput.collect(RecordWriterOutput.java:43) ~[flink-dist_2.12-1.12.1.jar:1.12.1]
statefun-worker_1 | at org.apache.flink.streaming.api.operators.CountingOutput.collect(CountingOutput.java:50) ~[flink-dist_2.12-1.12.1.jar:1.12.1]
statefun-worker_1 | at org.apache.flink.streaming.api.operators.CountingOutput.collect(CountingOutput.java:28) ~[flink-dist_2.12-1.12.1.jar:1.12.1]
statefun-worker_1 | at org.apache.flink.statefun.flink.core.translation.IngressRouterOperator$DownstreamCollector.forward(IngressRouterOperator.java:127) ~[statefun-flink-core.jar:3.0.0]
statefun-worker_1 | at org.apache.flink.statefun.sdk.io.Router$Downstream.forward(Router.java:67) ~[statefun-flink-distribution.jar:3.0.0]
statefun-worker_1 | at com.my.flink.EmbeddedModule$1.route(EmbeddedModule.java:47) ~[myflink-1.jar:?]
statefun-worker_1 | at com.my.flink.EmbeddedModule$1.route(EmbeddedModule.java:43) ~[myflink-1.jar:?]
statefun-worker_1 | at org.apache.flink.statefun.flink.core.translation.IngressRouterOperator.processElement(IngressRouterOperator.java:81) ~[statefun-flink-core.jar:3.0.0]
...
statefun-worker_1 | Caused by: java.lang.classCastException: class com.my.flink.Message cannot be cast to class com.google.protobuf.Message (com.my.flink.Message is in unnamed module of loader org.apache.flink.util.ChildFirstClassLoader @2aab3c1e; com.google.protobuf.Message is in unnamed module of loader 'app')
statefun-worker_1 | at org.apache.flink.statefun.flink.core.message.MessagePayloadSerializerPb.serialize(MessagePayloadSerializerPb.java:50) ~[statefun-flink-core.jar:3.0.0]
...
解决方法
由嵌入式函数发送/接收的消息默认假定为 Protobuf。您可以通过在 flink-conf.yaml 中设置以下键来使用 Kryo（甚至自定义序列化程序）：
statefun.message.serializer：WITH_KRYO_PAYLOADS
这并不是真正推荐的，因为随着时间的推移，您的应用程序将很难发展。
您仍然可以坚持使用 Protobuf，通过使用名为 StringValue 的内置 Protobuf 类型推迟字符串 -> 消息反序列化。
我采用了您粘贴的代码来使用 StringValue：
public class EmbeddedModule implements StatefulFunctionModule {
static final IngressIdentifier<StringValue> INGRESS = new IngressIdentifier<>(StringValue.class,"example","names");
private static final class MsgDeser implements KafkaIngressDeserializer<StringValue> {
private final ObjectMapper mapper = new ObjectMapper();
@Override
public StringValue deserialize(ConsumerRecord<byte[],byte[]> input) {
String json = new String(input.value(),StandardCharsets.UTF_8);
return StringValue.of(json);
}
}
public void configure(Map<String,String> globalConfiguration,Binder binder) {
binder.bindIngress(KafkaIngressBuilder.forIdentifier(INGRESS)
.withKafkaAddress("kafka:9092")
.withTopic("names")
.withDeserializer(MsgDeser.class)
.withConsumerGroupId("my-group-id")
.build());
binder.bindIngressRouter(INGRESS,new Router<StringValue>() {
@Override
public void route(StringValue m,Downstream<StringValue> ds) {
String json = StringValue.getValue();
String name = ... ; // extract the name from this JSON
ds.forward(GreeterFn.TYPE,name,m);
}
});
binder.bindFunctionProvider(GreeterFn.TYPE,x -> new GreeterFn());
}
}
将您的消息定义为 Portobuf 消息
避免双重反序列化（在路由器和函数处） 您可以定义以下 Protobuf 消息：
message MyMessage {
string name = 1;
string id = 2;
int visits = 3;
}
然后将json字符串转换为MyMessage的一个实例：
MyMessage.Builder builder = MyMessage.newBuilder();
JsonFormat.parser().merge(jsonString,builder);
MyMessage myMessage = builder.build();