jdk17 体验

作为LTS版本的java17 一定是未来，考虑将dawdler-series做一个java17的版本。所以需要先踩一下坑。

以下是一些新特性

306:	Restore Always-Strict Floating-Point Semantics
356:	Enhanced Pseudo-Random Number Generators
382:	New macOS Rendering Pipeline
391:	macOS/AArch64 Port
398:	Deprecate the Applet API for Removal
403:	Strongly Encapsulate JDK Internals
406:	Pattern Matching for switch (Preview)
407:	Remove RMI Activation
409:	Sealed Classes
410:	Remove the Experimental AOT and JIT Compiler
411:	Deprecate the Security Manager for Removal
412:	Foreign Function & Memory API (Incubator)
414:	Vector API (Second Incubator)
415:	Context-Specific Deserialization Filters

除了ZGC与JPMS其他无喜感,基本不关注。

本文记录 JPMS使用过程。

自行了解下 module-info.java

 

以下为代码实例

 

module-info.java

module unsafe {
requires java.base;
requires jdk.unsupported;
}

Test.java

package unsafe;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;

public class Test {
public static void main(String[] args) throws ClassNotFoundException, InstantiationException, IllegalAccessException, NoSuchMethodException, SecurityException, IllegalArgumentException, InvocationTargetException, NoSuchFieldException {
System.out.println("hello");
Class c = Class.forName("jdk.internal.misc.Unsafe");
System.out.println(c);
Method method = c.getMethod("getUnsafe", null);
method.setAccessible(true);
System.out.println(method.invoke(null, null));

}
}

以上代码很简单只是为了试验是否可以使用jdk.internal.misc.Unsafe.

 

因为 java17 jdk.internal.misc.Unsafe 在 java.base中并未exports,所以以上代码无法执行会报错。

 

 

各种玩法：

 

第一种 直接编译 javac

 

javac unsafe/Test.java

 

[srchen @bogon src]$ java unsafe.Test

hello

class jdk.internal.misc.Unsafe

Exception in thread "main" java.lang.reflect.InaccessibleObjectException: Unable to make public static jdk.internal.misc.Unsafe jdk.internal.misc.Unsafe.getUnsafe() accessible: module java.base does not "exports jdk.internal.misc" to unnamed module @5f8754e

at java.base/java.lang.reflect.AccessibleObject.checkCanSetAccessible(AccessibleObject.java:354)

at java.base/java.lang.reflect.AccessibleObject.checkCanSetAccessible(AccessibleObject.java:297)

at java.base/java.lang.reflect.Method.checkCanSetAccessible(Method.java:199)

at java.base/java.lang.reflect.Method.setAccessible(Method.java:193)

at unsafe.Test.main(Test.java:13)

 

报错...

 

采用 --add-opens 运行试试

[srchen @bogon src]$ java --add-opens java.base/jdk.internal.misc=ALL-UNNAMED unsafe.Test

hello

class jdk.internal.misc.Unsafe

jdk.internal.misc.Unsafe@4d7e1886

 

可以运行

 

 

模块方式

 

编译

javac mods/unsafe module-info.java unsafe/*.java

 

另一种

 

javac --add-exports java.base/jdk.internal.misc=unsafe -d mods/unsafe module-info.java unsafe/*.java

 

--add-exports一般用于ide

 

运行

[srchen @bogon src]$ java --module-path mods --add-opens=java.base/jdk.internal.misc=unsafe --module unsafe/unsafe.Test

hello

class jdk.internal.misc.Unsafe

jdk.internal.misc.Unsafe@77459877

{{o.name}}

{{m.name}}