DonHaul opened a new issue #9784:
URL: https://github.com/apache/pulsar/issues/9784
**Describe the bug**
A clear and concise description of what the bug is.
When using a reader to read a single message from a partitioned topic the
error The partitioned topic startMessageId is illegal appears:
```
Exception in thread "main"
org.apache.pulsar.client.api.PulsarClientException:
java.util.concurrent.ExecutionException:
org.apache.pulsar.client.api.PulsarClientException: The partitioned topic
startMessageId is illegal
at
org.apache.pulsar.client.api.PulsarClientException.unwrap(PulsarClientException.java:976)
at
org.apache.pulsar.client.impl.ReaderBuilderImpl.create(ReaderBuilderImpl.java:74)
```
I implemented the code in
https://pulsar.apache.org/docs/en/client-libraries-java/#reader which works for
non partitioned topics.
I just consumed and saved the msg id bytes into a file and then loaded that
file as the msg_id . Is any additional parameter needed to fetch partitioned
topics?
Consumer
```
Consumer consumer = client.newConsumer()
.topic("apache/pulsar/test-topic")
.subscriptionName("my-sub")
.subscribe();
// Wait for a message
Message msg = consumer.receive();
try {
byte[] by = msg.getMessageId().toByteArray();
FileUtils.writeByteArrayToFile(new File(".\\msg.bytes"), by);
}catch (Exception e){
System.out.println("ERROR");
e.printStackTrace();
}
```
Reader
```
byte[] msgIdBytes = FileUtils.readFileToByteArray(new
File(".\\msg.bytes"));// Some message ID byte array
System.out.println(msgIdBytes.length);
MessageId id = MessageId.fromByteArray(msgIdBytes);
System.out.println(id);
Reader reader = client.newReader()
.topic("apache/pulsar/test-topic")
.startMessageId(id)
.create();
Message message = reader.readNext();
// Process message
System.out.println(message.getMessageId());
client.close();
```
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