java – readResolve不工作？ ：出现了Guava的SerializedForm实例

在我们的一个数据结构的反序列化过程中(使用默认机制(没有自定义writeObject / readObject)),会出现一个ImmutableMap $SerializedForm实例(来自google的Guava库).

这样的实例不应该从guava的客户端看到,因为SerializedForm的实例被替换为readResolve(参见com.google.common.collect.Immutable类中的“writeReplace”).

因此反序列化失败,并显示以下消息：

java.lang.ClassCastException: cannot assign instance of com.google.common.collect.ImmutableMap$SerializedForm
to field .. of type java.util.Map in instance of com.blah.C

这是正确的,因为ImmutableMap $SerializedForm不是java.util.Map的子类型
它应该被替换.出了什么问题？

我们在com.blah.C类中没有自定义的writeObject / readObject.我们在父对象(包含com.blah.C)中有自定义序列化代码.

更新,这是堆栈跟踪的顶部：

java.lang.ClassCastException: cannot assign instance of com.google.common.collect.ImmutableSet$SerializedForm to field com.blah.ast.Automaton.bodyNodes of type java.util.Set in instance of com.blah.ast.Automaton
at java.io.ObjectStreamClass$FieldReflector.setObjFieldValues(ObjectStreamClass.java:2039)
at java.io.ObjectStreamClass.setObjFieldValues(ObjectStreamClass.java:1212)
at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:1952)
at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:1870)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1752)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1328)
at java.io.ObjectInputStream.readObject(ObjectInputStream.java:350)
at java.util.ArrayList.readObject(ArrayList.java:593)
at sun.reflect.GeneratedMethodAccessor9.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at java.io.ObjectStreamClass.invokeReadObject(ObjectStreamClass.java:974)
at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:1848)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1752)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1328)
at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:1946)
at java.io.ObjectInputStream.defaultReadObject(ObjectInputStream.java:479)
at com.blah.ast.AstNode.readObject(AstNode.java:189)
at sun.reflect.GeneratedMethodAccessor10.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at java.io.ObjectStreamClass.invokeReadObject(ObjectStreamClass.java:974)
at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:1848)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1752)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1328)
at java.io.ObjectInputStream.readObject(ObjectInputStream.java:350)
at java.util.ArrayList.readObject(ArrayList.java:593)
at sun.reflect.GeneratedMethodAccessor9.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at java.io.ObjectStreamClass.invokeReadObject(ObjectStreamClass.java:974)
at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:1848)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1752)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1328)
at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:1946)
at java.io.ObjectInputStream.defaultReadObject(ObjectInputStream.java:479)
at com.blah.ast.AstNode.readObject(AstNode.java:189)

解决方法:

本周,我们又面临这个错误;但我找到了根本原因. ObjectInputStream使用的类加载器是高度依赖于上下文的(有些人会说是不确定的).以下是Sun文档的相关部分(它是ObjectInputStream#resolveClass(ObjectStreamClass)的摘录)：

[The class loader] is determined as follows: if there is a method on the current thread’s stack whose declaring class was defined by a user-defined class loader (and was not a generated to implement reflective invocations), then it is the class loader corresponding to the closest such method to the currently executing frame; otherwise, it is null. If this call results in a ClassNotFoundException and the name of the passed ObjectStreamClass instance is the Java language keyword for a primitive type or void, then the Class object representing that primitive type or void will be returned (e.g., an ObjectStreamClass with the name “int” will be resolved to Integer.TYPE). Otherwise, the ClassNotFoundException will be thrown to the caller of this method.

在我们的应用程序中,我们有一个Eclipse插件B依赖于一个实用程序专用插件A.我们反序列化其类在B中的对象,但反序列化是在A中启动的(在那里创建一个ObjectInputStream),这就是问题所在.很少(即取决于文档所说的调用堆栈)反序列化选择了错误的类加载器(一个无法加载B类的加载器).为了解决这个问题,我们将一个适当的加载器从顶级反序列化调用程序(在B中)传递给A中的实用程序方法.此方法现在使用自定义ObjectInputStream,如下所示(注意自由变量“loader”)：

ObjectInputStream ois = new ObjectInputStream(new FileInputStream(file)) {
                @SuppressWarnings("rawtypes")
                @Override
                protected Class resolveClass(ObjectStreamClass objectStreamClass)
                        throws IOException, ClassNotFoundException {
                    return Class.forName(objectStreamClass.getName(), true, loader);
                }
            };

标签：classcastexception,java,guava,deserialization
来源： https://codeday.me/bug/20191004/1853674.html