Gson序列化Kotlin的Arena类时触发InaccessibleObjectException异常

报错堆栈 #

Caused by: java.lang.reflect.InaccessibleObjectException: Unable to make field private java.lang.Object java.lang.ref.Reference.referent accessible: module java.base does not "opens java.lang.ref" to unnamed module @40444e23
    at java.lang.reflect.AccessibleObject.checkCanSetAccessible(AccessibleObject.java:354) ~[?:?]
    at java.lang.reflect.AccessibleObject.checkCanSetAccessible(AccessibleObject.java:297) ~[?:?]
    at java.lang.reflect.Field.checkCanSetAccessible(Field.java:180) ~[?:?]
    at java.lang.reflect.Field.setAccessible(Field.java:174) ~[?:?]
    at com.google.gson.internal.reflect.UnsafeReflectionAccessor.makeAccessible(UnsafeReflectionAccessor.java:44) ~[gson-2.8.9.jar:?]
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.getBoundFields(ReflectiveTypeAdapterFactory.java:159) ~[gson-2.8.9.jar:?]
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.create(ReflectiveTypeAdapterFactory.java:102) ~[gson-2.8.9.jar:?]
    at com.google.gson.Gson.getAdapter(Gson.java:489) ~[gson-2.8.9.jar:?]
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.createBoundField(ReflectiveTypeAdapterFactory.java:117) ~[gson-2.8.9.jar:?]
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.getBoundFields(ReflectiveTypeAdapterFactory.java:166) ~[gson-2.8.9.jar:?]
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.create(ReflectiveTypeAdapterFactory.java:102) ~[gson-2.8.9.jar:?]
    at com.google.gson.Gson.getAdapter(Gson.java:489) ~[gson-2.8.9.jar:?]
    at com.google.gson.internal.bind.CollectionTypeAdapterFactory.create(CollectionTypeAdapterFactory.java:53) ~[gson-2.8.9.jar:?]
    at com.google.gson.Gson.getAdapter(Gson.java:489) ~[gson-2.8.9.jar:?]
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.createBoundField(ReflectiveTypeAdapterFactory.java:117) ~[gson-2.8.9.jar:?]
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.getBoundFields(ReflectiveTypeAdapterFactory.java:166) ~[gson-2.8.9.jar:?]
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.create(ReflectiveTypeAdapterFactory.java:102) ~[gson-2.8.9.jar:?]
    at com.google.gson.Gson.getAdapter(Gson.java:489) ~[gson-2.8.9.jar:?]
    at com.google.gson.Gson.toJson(Gson.java:727) ~[gson-2.8.9.jar:?]
    at com.google.gson.Gson.toJson(Gson.java:714) ~[gson-2.8.9.jar:?]
    at com.google.gson.Gson.toJson(Gson.java:669) ~[gson-2.8.9.jar:?]
    at com.google.gson.Gson.toJson(Gson.java:649) ~[gson-2.8.9.jar:?]
    at de.carina.pixelsjump.util.arena.Arena.saveArena(Arena.kt:35) ~[PixelsJumpRemastered-1.0.0-all.jar:?]
    at de.carina.pixelsjump.commands.setup.ArenaFinish.execute(ArenaFinish.kt:53) ~[PixelsJumpRemastered-1.0.0-all.jar:?]
    at de.carina.pixelsjump.commands.util.CommandRegister.onCommand(CommandRegister.kt:36) ~[PixelsJumpRemastered-1.0.0-all.jar:?]
    at org.bukkit.command.PluginCommand.execute(PluginCommand.java:45) ~[paper-api-1.19-R0.1-SNAPSHOT.jar:?]
    ... 26 more
Caused by: java.lang.reflect.InaccessibleObjectException: Unable to make field private java.lang.Object java.lang.ref.Reference.referent accessible: module java.base does not "opens java.lang.ref" to unnamed module @40444e23

待序列化的Arena类代码 #

class Arena(val name: String) {
    val checkPoints: MutableList<Location> = mutableListOf()
    var startLocation: Location? = null
     var finishLocation: Location? = null
     var backLocation: Location? = null
    val players = mutableSetOf<Player>()

    @Transient
    private val file: File = File("plugins/PixelsJumpRemastered/arenas/$name.json")
    var single: Boolean = false
    var damage: Boolean = false

    fun saveArena() {
        val gson = GsonBuilder().setPrettyPrinting().create()
        var json = gson.toJson(this)
        file.writeText(json)
    }


    fun addCheckpointLocation(location: Location) {
        checkPoints.add(location.block.getRelative(BlockFace.DOWN).location.toCenterLocation())
    }
}

解决思路 #

1. 排除无法序列化的对象（核心修复） #

报错根源是Gson尝试序列化players集合中的Player对象，而Player是Bukkit的引用类型，内部包含Reference相关字段，Java 9+的模块系统禁止Gson通过反射访问这些内部字段。

给players字段加上@Transient注解，让Gson跳过序列化：

@Transient
val players = mutableSetOf<Player>()

2. 升级Gson版本 #

当前使用的Gson 2.8.9对Java模块系统兼容性较差，升级到Gson 2.10.1及以上版本，新版本优化了反射访问逻辑，能更好适配Java 9+的模块规则。

3. 为Bukkit类型自定义TypeAdapter #

Location这类Bukkit对象默认无法被Gson正确序列化/反序列化，需自定义TypeAdapter实现转换：

class LocationTypeAdapter : TypeAdapter<Location>() {
    override fun write(out: JsonWriter, value: Location?) {
        if (value == null) {
            out.nullValue()
            return
        }
        out.beginObject()
        out.name("world").value(value.world.name)
        out.name("x").value(value.x)
        out.name("y").value(value.y)
        out.name("z").value(value.z)
        out.name("yaw").value(value.yaw)
        out.name("pitch").value(value.pitch)
        out.endObject()
    }

    override fun read(`in`: JsonReader): Location? {
        `in`.beginObject()
        var worldName: String? = null
        var x = 0.0
        var y = 0.0
        var z = 0.0
        var yaw = 0f
        var pitch = 0f
        while (`in`.hasNext()) {
            when (`in`.nextName()) {
                "world" -> worldName = `in`.nextString()
                "x" -> x = `in`.nextDouble()
                "y" -> y = `in`.nextDouble()
                "z" -> z = `in`.nextDouble()
                "yaw" -> yaw = `in`.nextFloat()
                "pitch" -> pitch = `in`.nextFloat()
            }
        }
        `in`.endObject()
        val world = Bukkit.getWorld(worldName ?: return null) ?: return null
        return Location(world, x, y, z, yaw, pitch)
    }
}

创建Gson实例时注册该Adapter：

val gson = GsonBuilder()
    .setPrettyPrinting()
    .registerTypeAdapter(Location::class.java, LocationTypeAdapter())
    .create()

4. JVM参数临时绕过（不推荐） #

若以上方案无法快速生效，可添加JVM启动参数临时允许模块反射访问：

--add-opens java.base/java.lang.ref=ALL-UNNAMED

此方案仅作临时应急，会破坏Java模块系统的封装性，不建议长期使用。

内容的提问来源于stack exchange，提问作者Carina Sophie