WebFlux functional endpoint, how to return a ServerResponse with retrieved data and no unnecessary block/wait? - spring-boot

Question

I am totally new to reactive code and after a number of tutorials and youtube videos I am trying to setup a tiny test application using functional endpoints; a simple RouterFunction, RouterHandler and Repository. The problem is how to return an object in the ServerResponse from the respository to the caller, without causing any unnecessary blocking?
I am using Postman for testing. Here's the interesting parts of my test application:
#Configuration
public class BookRouter {
#Autowired
BookRepositoryImpl bookRepository;
#Bean
public RouterFunction<ServerResponse> bookRoutes() {
BookHandler bookHandler = new BookHandler(bookRepository);
return RouterFunctions
.nest(path("/api/books"),
route(GET("/{group}/{name}").and(accept(ALL)), bookHandler::getBook)
);
}
}
#Repository
public class BookRepositoryImpl implements BookRepository {
private final ReactiveMongoTemplate mongoTemplate;
#Autowired
public BookRepositoryImpl(ReactiveMongoTemplate mongoTemplate) {
this.mongoTemplate = mongoTemplate;
}
#Override
public Mono<Book> findByName(String group, String name) {
Query query = new Query(Criteria.where("group").is(group).and("name").is(name));
return mongoTemplate.findOne(query, Book.class);
}
}
public class BookHandler {
public Mono<ServerResponse> getBook(ServerRequest request) {
String group = request.pathVariable("group");
String name = request.pathVariable("name");
bookRepository
.findByName(group, name)
.subscribe(
ok -> System.out.println("findByName " + ok),
error -> System.err.println("Error: " + error));
return ServerResponse
.accepted()
.contentType(MediaType.TEXT_PLAIN)
.bodyValue("Request queued");
}
}
When I have the code as shown above, the expected data is printed out in subscribe(ok -> ...), but I haven't figured out how to return this data in the ServerResponse.
If I change the code in getBook() to
return setting
.flatMap(s -> ServerResponse
.ok()
.contentType(MediaType.APPLICATION_JSON)
.bodyValue(s))
.switchIfEmpty(NOT_FOUND);
the returned bodyValue is empty, although I can see that it was retrieved from the database.
Any advice on what I am missing is most appreciated.
Update
I am using MongoDB Compass to view and verify the content of the database.
Debug logging is enabled in application.properties with logging.level.root=DEBUGso the Spring classes write some info in the terminal window. Parts of the somewhat anonymized log is as follows:
2020-09-05 21:37:02.688 DEBUG 32720 --- [ctor-http-nio-3] o.s.w.r.f.s.s.RouterFunctionMapping : [96ef6152-1] Mapped to com.sample.book.BookRouter$$Lambda$586/0x0000000800540040#3b0bf8e0
2020-09-05 21:37:02.717 DEBUG 32720 --- [ctor-http-nio-3] o.s.d.m.core.ReactiveMongoTemplate : findOne using query: { "group" : "Thriller", "name" : "The Shining"} fields: Document{{}} for class: class com.sample.book.Book in collection: book
2020-09-05 21:37:02.734 DEBUG 32720 --- [ctor-http-nio-3] o.s.d.m.core.ReactiveMongoTemplate : findOne using query: { "group" : "Thriller", "name" : "The Shining"} fields: {} in db.collection: book.book
2020-09-05 21:37:02.751 DEBUG 32720 --- [ctor-http-nio-3] org.mongodb.driver.protocol.command : Sending command '{"find": "book", "filter": {"group": "Thriller", "name": "The Shining"}, "limit": 1, "singleBatch": true, "$db": "book"}' with request id 7 to database book on connection [connectionId{localValue:2, serverValue:217}] to server localhost:27017
2020-09-05 21:37:02.766 DEBUG 32720 --- [ntLoopGroup-3-2] org.mongodb.driver.protocol.command : Execution of command with request id 7 completed successfully in 16.24 ms on connection [connectionId{localValue:2, serverValue:217}] to server localhost:27017
2020-09-05 21:37:02.837 DEBUG 32720 --- [ntLoopGroup-3-2] o.s.http.codec.json.Jackson2JsonEncoder : [96ef6152-1] Encoding [_id=5f53692af0a02d3af8a7fed9, group=Thriller, name=The Shining, value=in]]
2020-09-05 21:37:02.853 DEBUG 32720 --- [ctor-http-nio-3] r.n.http.server.HttpServerOperations : [id: 0x96ef6152, L:/0:0:0:0:0:0:0:1:8088 - R:/0:0:0:0:0:0:0:1:50248] Decreasing pending responses, now 0
2020-09-05 21:37:02.879 DEBUG 32720 --- [ctor-http-nio-3] o.s.w.s.adapter.HttpWebHandlerAdapter : [96ef6152-1] Completed 200 OK
2020-09-05 21:37:02.905 DEBUG 32720 --- [ctor-http-nio-3] r.n.http.server.HttpServerOperations : [id: 0x96ef6152, L:/0:0:0:0:0:0:0:1:8088 - R:/0:0:0:0:0:0:0:1:50248] Last HTTP response frame
2020-09-05 21:37:02.931 DEBUG 32720 --- [ctor-http-nio-3] r.n.http.server.HttpServerOperations : [id: 0x96ef6152, L:/0:0:0:0:0:0:0:1:8088 - R:/0:0:0:0:0:0:0:1:50248] Last HTTP packet was sent, terminating the channel

Answer 1

I found the problem. I had forgot to implement getters in the Book class holding the #Document. I am surprised that there were no error message or warning when they were missing.
As soon as I inserted them, the result was returned as expected from this code:
return setting
.flatMap(s -> ServerResponse
.ok()
.contentType(MediaType.APPLICATION_JSON)
.bodyValue(s))
.switchIfEmpty(NOT_FOUND);
Here is the data as returned to Postman after the fix:
{
"_id": "5f53692af0a02d3af8a7fed9",
"group": "Thrillers",
"name": "The Shining",
"value": "in"
}
Thank you to #caco3 for helping me find the problem!
Here is my updated Book.java.
#Document
#CompoundIndex(name = "group-name", def = "{'group':1, 'name':1}", unique = true) // Requires auto-index-creation in application.properties
public class Book {
#Id
private String _id;
private String group;
private String name;
private String value;
public Book() {
}
public Book(String group, String name, String value) {
this.group = group;
this.name = name;
this.value = value;
}
#Override
public String toString() {
StringBuilder s = new StringBuilder('[');
s.append("_id=").append(_id);
s.append(", group=").append(group);
s.append(", name=").append(name);
s.append(", value=").append(value);
s.append(']');
return s.toString();
}
public String get_id() {
return _id;
}
public String getGroup() {
return group;
}
public void setGroup(String group) {
this.group = group;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getValue() {
return value;
}
public void setValue(String value) {
this.value = value;
}
}