Jackson + ProGuard：无法反序列化使用自定义反序列化器的类

Question

我的应用程序使用Jackson。我使用以下配置基本上可以使最小化构建工作：

# don't obfuscate Jackson classes
-keep class com.fasterxml.** { *; }

# don't strip runtime annotations
-keepattributes RuntimeVisibleAnnotations

# keep members with Jackson annotations
-keepclassmembers public class * {
     @com.fasterxml.jackson.annotation.JsonCreator *;
     @com.fasterxml.jackson.annotation.JsonProperty *;
}

但是，最小化的构建仍然无法反序列化使用自定义反序列化程序的一个类，该程序又使用工厂。该工厂、反序列化程序和映射器都是由Dagger2生成的。错误信息如下：

com.fasterxml.jackson.databind.JsonMappingException: No suitable constructor found for type [simple type, class com.mycompany.myapp.c.y]: can not instantiate from JSON object (missing default constructor or creator, or perhaps need to add/enable type information?)
            at [Source: N/A; line: -1, column: -1]
            at com.fasterxml.jackson.databind.deser.BeanDeserializerBase.deserializeFromObjectUsingNonDefault(Unknown Source)
            at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserializeFromObject(Unknown Source)
            at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(Unknown Source)
            at com.fasterxml.jackson.databind.ObjectMapper._readValue(Unknown Source)
            at com.fasterxml.jackson.databind.ObjectMapper.readValue(Unknown Source)
            at com.fasterxml.jackson.databind.ObjectMapper.treeToValue(Unknown Source)
            at com.mycompany.myapp.c.x.a(Unknown Source)
            at com.mycompany.myapp.c.x.a(Unknown Source)
            at com.mycompany.myapp.c.x.deserialize(Unknown Source)
            at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(Unknown Source)
            at com.fasterxml.jackson.databind.ObjectMapper.readValue(Unknown Source)
            at com.mycompany.myapp.c.ag.d(Unknown Source)
            at com.mycompany.myapp.c.ag.a(Unknown Source)
            at com.mycompany.myapp.c.at.run(Unknown Source)
            at android.os.Handler.handleCallback(Handler.java:605)
            at android.os.Handler.dispatchMessage(Handler.java:92)
            at android.os.Looper.loop(Looper.java:137)
            at android.app.ActivityThread.main(ActivityThread.java:4508)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:511)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:809)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:576)
            at dalvik.system.NativeStart.main(Native Method)

错误信息表明我的类缺少默认构造函数，这是确实的，因为实例是由自定义反序列化器使用工厂创建的。当我禁用ProGuard时，这个方法可以正常工作。我需要做什么才能让它与ProGuard一起工作？

- Kevin Krumwiede

Answer 1

我意外发现了这个方便的故障排除技巧：

-keepnames class * { *; }

这揭示了真正的罪犯是我定制反序列化程序中的一个私有静态嵌套类。 解决方案是从此选项的类说明符中删除public：

-keepclassmembers class * {
     @com.fasterxml.jackson.annotation.JsonCreator *;
     @com.fasterxml.jackson.annotation.JsonProperty *;
}

- Kevin Krumwiede