ReflectionAccessFilter.java
/*
* Copyright (C) 2022 Google Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.google.gson;
import com.google.gson.internal.ReflectionAccessFilterHelper;
import java.lang.reflect.AccessibleObject;
/**
* Filter for determining whether reflection based serialization and
* deserialization is allowed for a class.
*
* <p>A filter can be useful in multiple scenarios, for example when
* upgrading to newer Java versions which use the Java Platform Module
* System (JPMS). A filter then allows to {@linkplain FilterResult#BLOCK_INACCESSIBLE
* prevent making inaccessible members accessible}, even if the used
* Java version might still allow illegal access (but logs a warning),
* or if {@code java} command line arguments are used to open the inaccessible
* packages to other parts of the application. This interface defines some
* convenience filters for this task, such as {@link #BLOCK_INACCESSIBLE_JAVA}.
*
* <p>A filter can also be useful to prevent mixing model classes of a
* project with other non-model classes; the filter could
* {@linkplain FilterResult#BLOCK_ALL block all reflective access} to
* non-model classes.
*
* <p>A reflection access filter is similar to an {@link ExclusionStrategy}
* with the major difference that a filter will cause an exception to be
* thrown when access is disallowed while an exclusion strategy just skips
* fields and classes.
*
* @see GsonBuilder#addReflectionAccessFilter(ReflectionAccessFilter)
* @since 2.9.1
*/
public interface ReflectionAccessFilter {
/**
* Result of a filter check.
*
* @since 2.9.1
*/
enum FilterResult {
/**
* Reflection access for the class is allowed.
*
* <p>Note that this does not affect the Java access checks in any way,
* it only permits Gson to try using reflection for a class. The Java
* runtime might still deny such access.
*/
ALLOW,
/**
* The filter is indecisive whether reflection access should be allowed.
* The next registered filter will be consulted to get the result. If
* there is no next filter, this result acts like {@link #ALLOW}.
*/
INDECISIVE,
/**
* Blocks reflection access if a member of the class is not accessible
* by default and would have to be made accessible. This is unaffected
* by any {@code java} command line arguments being used to make packages
* accessible, or by module declaration directives which <i>open</i> the
* complete module or certain packages for reflection and will consider
* such packages inaccessible.
*
* <p>Note that this <b>only works for Java 9 and higher</b>, for older
* Java versions its functionality will be limited and it might behave like
* {@link #ALLOW}. Access checks are only performed as defined by the Java
* Language Specification (<a href="https://docs.oracle.com/javase/specs/jls/se11/html/jls-6.html#jls-6.6">JLS 11 §6.6</a>),
* restrictions imposed by a {@link SecurityManager} are not considered.
*
* <p>This result type is mainly intended to help enforce the access checks of
* the Java Platform Module System. It allows detecting illegal access, even if
* the used Java version would only log a warning, or is configured to open
* packages for reflection using command line arguments.
*
* @see AccessibleObject#canAccess(Object)
*/
BLOCK_INACCESSIBLE,
/**
* Blocks all reflection access for the class. Other means for serializing
* and deserializing the class, such as a {@link TypeAdapter}, have to
* be used.
*/
BLOCK_ALL
}
/**
* Blocks all reflection access to members of standard Java classes which are
* not accessible by default. However, reflection access is still allowed for
* classes for which all fields are accessible and which have an accessible
* no-args constructor (or for which an {@link InstanceCreator} has been registered).
*
* <p>If this filter encounters a class other than a standard Java class it
* returns {@link FilterResult#INDECISIVE}.
*
* <p>This filter is mainly intended to help enforcing the access checks of
* Java Platform Module System. It allows detecting illegal access, even if
* the used Java version would only log a warning, or is configured to open
* packages for reflection. However, this filter <b>only works for Java 9 and
* higher</b>, when using an older Java version its functionality will be
* limited.
*
* <p>Note that this filter might not cover all standard Java classes. Currently
* only classes in a {@code java.*} or {@code javax.*} package are considered. The
* set of detected classes might be expanded in the future without prior notice.
*
* @see FilterResult#BLOCK_INACCESSIBLE
*/
ReflectionAccessFilter BLOCK_INACCESSIBLE_JAVA = new ReflectionAccessFilter() {
@Override public FilterResult check(Class<?> rawClass) {
return ReflectionAccessFilterHelper.isJavaType(rawClass)
? FilterResult.BLOCK_INACCESSIBLE
: FilterResult.INDECISIVE;
}
};
/**
* Blocks all reflection access to members of standard Java classes.
*
* <p>If this filter encounters a class other than a standard Java class it
* returns {@link FilterResult#INDECISIVE}.
*
* <p>This filter is mainly intended to prevent depending on implementation
* details of the Java platform and to help applications prepare for upgrading
* to the Java Platform Module System.
*
* <p>Note that this filter might not cover all standard Java classes. Currently
* only classes in a {@code java.*} or {@code javax.*} package are considered. The
* set of detected classes might be expanded in the future without prior notice.
*
* @see #BLOCK_INACCESSIBLE_JAVA
* @see FilterResult#BLOCK_ALL
*/
ReflectionAccessFilter BLOCK_ALL_JAVA = new ReflectionAccessFilter() {
@Override public FilterResult check(Class<?> rawClass) {
return ReflectionAccessFilterHelper.isJavaType(rawClass)
? FilterResult.BLOCK_ALL
: FilterResult.INDECISIVE;
}
};
/**
* Blocks all reflection access to members of standard Android classes.
*
* <p>If this filter encounters a class other than a standard Android class it
* returns {@link FilterResult#INDECISIVE}.
*
* <p>This filter is mainly intended to prevent depending on implementation
* details of the Android platform.
*
* <p>Note that this filter might not cover all standard Android classes. Currently
* only classes in an {@code android.*} or {@code androidx.*} package, and standard
* Java classes in a {@code java.*} or {@code javax.*} package are considered. The
* set of detected classes might be expanded in the future without prior notice.
*
* @see FilterResult#BLOCK_ALL
*/
ReflectionAccessFilter BLOCK_ALL_ANDROID = new ReflectionAccessFilter() {
@Override public FilterResult check(Class<?> rawClass) {
return ReflectionAccessFilterHelper.isAndroidType(rawClass)
? FilterResult.BLOCK_ALL
: FilterResult.INDECISIVE;
}
};
/**
* Blocks all reflection access to members of classes belonging to programming
* language platforms, such as Java, Android, Kotlin or Scala.
*
* <p>If this filter encounters a class other than a standard platform class it
* returns {@link FilterResult#INDECISIVE}.
*
* <p>This filter is mainly intended to prevent depending on implementation
* details of the platform classes.
*
* <p>Note that this filter might not cover all platform classes. Currently it
* combines the filters {@link #BLOCK_ALL_JAVA} and {@link #BLOCK_ALL_ANDROID},
* and checks for other language-specific platform classes like {@code kotlin.*}.
* The set of detected classes might be expanded in the future without prior notice.
*
* @see FilterResult#BLOCK_ALL
*/
ReflectionAccessFilter BLOCK_ALL_PLATFORM = new ReflectionAccessFilter() {
@Override public FilterResult check(Class<?> rawClass) {
return ReflectionAccessFilterHelper.isAnyPlatformType(rawClass)
? FilterResult.BLOCK_ALL
: FilterResult.INDECISIVE;
}
};
/**
* Checks if reflection access should be allowed for a class.
*
* @param rawClass
* Class to check
* @return
* Result indicating whether reflection access is allowed
*/
FilterResult check(Class<?> rawClass);
}