Jdk16中JcTree的使用问题

因为jdk16进行了强制的模块化使用限制, 需要增加add-opens去进行模块的放开, 但是如果每次都需要在项目pom文件或者启动命令中增加，非常不优雅。而且很多重复的命令。
所以想有没有更好的办法去解决。
看了lombok1.18.20中的解决方法，这边来总结一下。lombok这个问题的讨论

pom文件时候添加

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<build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.8.1</version>
                <configuration>
                    <source>1.8</source>
                    <target>1.8</target>
                    <showDeprecation>true</showDeprecation>
                    <showWarnings>true</showWarnings>
                    <fork>true</fork>
                    <compilerArgs>
                        <!--                        <arg>-Werror</arg>-->
                        <arg>-Xlint:all</arg>
                        <arg>-J--add-opens=jdk.compiler/com.sun.tools.javac.code=ALL-UNNAMED</arg>
                        <arg>-J--add-opens=jdk.compiler/com.sun.tools.javac.comp=ALL-UNNAMED</arg>
                        <arg>-J--add-opens=jdk.compiler/com.sun.tools.javac.file=ALL-UNNAMED</arg>
                        <arg>-J--add-opens=jdk.compiler/com.sun.tools.javac.main=ALL-UNNAMED</arg>
                        <arg>-J--add-opens=jdk.compiler/com.sun.tools.javac.model=ALL-UNNAMED</arg>
                        <arg>-J--add-opens=jdk.compiler/com.sun.tools.javac.parser=ALL-UNNAMED</arg>
                        <arg>-J--add-opens=jdk.compiler/com.sun.tools.javac.processing=ALL-UNNAMED</arg>
                        <arg>-J--add-opens=jdk.compiler/com.sun.tools.javac.tree=ALL-UNNAMED</arg>
                        <arg>-J--add-opens=jdk.compiler/com.sun.tools.javac.util=ALL-UNNAMED</arg>
                    </compilerArgs>
                </configuration>
            </plugin>
        </plugins>
    </build>

注解解析器添加

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public abstract class Example extends AbstractProcessor {
    @Override
    public final synchronized void init(ProcessingEnvironment processingEnv) {
    }
    static {
        addOpens();
    }
    public static void addOpens() {
        Class<?> cModule;
        try {
            cModule = Class.forName("java.lang.Module");
        } catch (ClassNotFoundException e) {
            return; //jdk8-; this is not needed.
        }

        Unsafe unsafe = getUnsafe();
        Object jdkCompilerModule = getJdkCompilerModule();
        Object ownModule = getOwnModule();
        String[] allPkgs = {
            "com.sun.tools.javac.code",
            "com.sun.tools.javac.comp",
            "com.sun.tools.javac.file",
            "com.sun.tools.javac.main",
            "com.sun.tools.javac.model",
            "com.sun.tools.javac.parser",
            "com.sun.tools.javac.processing",
            "com.sun.tools.javac.tree",
            "com.sun.tools.javac.util",
            "com.sun.tools.javac.jvm",
            "com.sun.tools.javac.api",
            };

        try {
            Method m = cModule.getDeclaredMethod("implAddOpens", String.class, cModule);
            long firstFieldOffset = getFirstFieldOffset(unsafe);
            unsafe.putBooleanVolatile(m, firstFieldOffset, true);
            for (String p : allPkgs) {
                m.invoke(jdkCompilerModule, p, ownModule);
            }
        } catch (Exception ignore) {}
    }

    private static Unsafe getUnsafe() {
        try {
            Field theUnsafe = Unsafe.class.getDeclaredField("theUnsafe");
            theUnsafe.setAccessible(true);
            return (Unsafe) theUnsafe.get(null);
        } catch (Exception e) {
            return null;
        }
    }

    private static Object getJdkCompilerModule() {
        try {
            Class<?> cModuleLayer = Class.forName("java.lang.ModuleLayer");
            Method mBoot = cModuleLayer.getDeclaredMethod("boot");
            Object bootLayer = mBoot.invoke(null);
            Class<?> cOptional = Class.forName("java.util.Optional");
            Method mFindModule = cModuleLayer.getDeclaredMethod("findModule", String.class);
            Object oCompilerO = mFindModule.invoke(bootLayer, "jdk.compiler");
            return cOptional.getDeclaredMethod("get").invoke(oCompilerO);
        } catch (Exception e) {
            return null;
        }
    }

    private static Object getOwnModule() {
        try {
            Method m = Permit.getMethod(Class.class, "getModule");
            return m.invoke(BaseProcessor.class);
        } catch (Exception e) {
            return null;
        }
    }

    private static long getFirstFieldOffset(Unsafe unsafe) {
        try {
            return unsafe.objectFieldOffset(Parent.class.getDeclaredField("first"));
        } catch (NoSuchFieldException e) {
            // can't happen.
            throw new RuntimeException(e);
        } catch (SecurityException e) {
            // can't happen
            throw new RuntimeException(e);
        }
    }

    public static class Parent {
        boolean first;
    }
}

其中调用了

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long firstFieldOffset = getFirstFieldOffset(unsafe);
unsafe.putBooleanVolatile(m, firstFieldOffset, true);

其中的含义不太能清楚，看起来是个激活模块的初始化操作，去除之后添加模块权限的操作是会失效的。

有懂的大佬希望可以告知一下是不是这样

在注解解析器中添加上诉代码后就可以正常在java16中使用jcTree啦

最小demo项目地址

Wish.

Do.

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