Reactive方式返回Token遇序列化异常：无UniOnItemTransform序列化器

问题描述 #

在使用Hilla的@BrowserCallable接口AuthenticationApi中，尝试通过Reactive方式返回Token时，遭遇序列化异常：

Failed to serialize endpoint 'AuthenticationApi' method 'token' response. Double check method's return type or specify a custom mapper bean with qualifier 'endpointMapperFactory': com.fasterxml.jackson.databind.exc.InvalidDefinitionException: No serializer found for class io.smallrye.mutiny.operators.uni.UniOnItemTransform and no properties discovered to create BeanSerializer (to avoid exception, disable SerializationFeature.FAIL_ON_EMPTY_BEANS)

核心代码：

@Inject
private final CurrentIdentityAssociation identityAssociation;

public Uni<String> token() {
    return identityAssociation.getDeferredIdentity()
        .onItem().transform(identity -> identity.getCredential(AccessTokenCredential.class))
        .onItem().transform(accessTokenCredential -> accessTokenCredential.getToken());
}

完整接口类：

package net.shamil.dcc.api;

import java.util.List;

import com.vaadin.flow.server.auth.AnonymousAllowed;

import dev.hilla.BrowserCallable;
import dev.hilla.Nonnull;
import io.quarkus.oidc.AccessTokenCredential;
import io.quarkus.oidc.UserInfo;
import io.quarkus.security.identity.CurrentIdentityAssociation;
import io.smallrye.mutiny.Uni;
import lombok.AllArgsConstructor;
import net.shamil.dcc.authentication.OidcUser;
import net.shamil.dcc.authentication.SingleSignOnContext;
import net.shamil.dcc.authentication.SingleSignOnData;

@BrowserCallable
@AnonymousAllowed
@AllArgsConstructor
public class AuthenticationApi {
    private final SingleSignOnContext context;
    private final UserInfo userInfo;
    private final CurrentIdentityAssociation identityAssociation;


    public @Nonnull SingleSignOnData fetchAll() {
        return context.getSingleSignOnData();
    }

    // public String token() {
    //     return Optional.ofNullable(securityIdentity.getCredential(AccessTokenCredential.class)).map(token -> token.getToken()).orElse(null);
    // }

    public Uni<String> token() {
        return identityAssociation.getDeferredIdentity()
        .onItem().transform(identity -> identity.getCredential(AccessTokenCredential.class))
        .onItem().transform(accessTokenCredential -> accessTokenCredential.getToken());
    }

    public @Nonnull List<@Nonnull String> getRegisteredProviders() {
        return context.getRegisteredProviders();
    }

    public OidcUser getAuthenticatedUser() {
        return context.getSingleSignOnData().isAuthenticated() ? OidcUser.fromUserInfo(userInfo) : null;
    }
}

当前依赖包含：

quarkus-resteasy-reactive
quarkus-resteasy-reactive-jackson
quarkus-oidc-client-reactive-filter

原因分析 #

Hilla的端点序列化机制默认未配置对SmallRye Mutiny Uni类型的支持，Jackson无法找到对应的序列化器，因此抛出序列化异常。

解决方案 #

方案1：添加Mutiny-Jackson序列化依赖（推荐） #

在pom.xml中添加SmallRye Mutiny与Jackson的集成依赖，让Jackson能够正确序列化Uni类型：

<dependency>
    <groupId>io.smallrye</groupId>
    <artifactId>smallrye-mutiny-jackson</artifactId>
</dependency>

添加后，Hilla端点会自动订阅Uni并返回最终的String结果，无需修改现有代码。

方案2：改为同步返回String（适合不需要Reactive的场景） #

如果业务场景允许同步获取Token，可以修改token()方法，通过await()获取Uni的结果：

public String token() {
    return Optional.ofNullable(identityAssociation.getDeferredIdentity()
            .await().indefinitely()
            .getCredential(AccessTokenCredential.class))
            .map(AccessTokenCredential::getToken)
            .orElse(null);
}

注意：await().indefinitely()会阻塞当前线程，需确保在允许阻塞的上下文环境中使用。

方案3：临时禁用Jackson空Bean序列化检查（不推荐） #

仅作为临时调试手段，添加配置绕过异常，但无法正确返回Token：
在application.properties中添加：

quarkus.jackson.serialization.fail-on-empty-beans=false

内容的提问来源于stack exchange，提问作者bear