Java - Object#finalize在JDK9中被标记废弃了！

时间：2022年12月6日01:34:10
目录：
① 为什么要废弃？
② 废弃后，使用什么方式主动监测对象是否被回收？

一、为什么要废弃？

⚡注意：废弃≠移除

二、可以使用什么方法检测对象被回收呢？（使用Cleaner✔️）

• 可参考源码：DirectByteBuffer⚡⚡⚡
  • import jdk.internal.ref.Cleaner;
  • –add-opens java.base/jdk.internal.ref=ALL-UNNAMED → 请继续阅读【三】，将会使用另一个Cleaner🚀

Cleaner使用示例：

import java.util.concurrent.TimeUnit;public class CleanerTest {public static void main(String[] args) {User user1 = new User();User user2 = new User();System.out.println(user1);System.out.println(user2);System.gc();user1 = user2 = null;System.gc();try { TimeUnit.SECONDS.sleep(3); } catch (InterruptedException e) { throw new RuntimeException(e); }}
}或者public class CleanerTest {public static void main(String[] args) {try (User user1 = new User();User user2 = new User();) {System.out.println(user1);System.out.println(user2);}}
}

import com.baomidou.mybatisplus.core.toolkit.IdWorker;
import jdk.internal.ref.Cleaner;
import lombok.EqualsAndHashCode;
import lombok.ToString;import java.io.Closeable;@EqualsAndHashCode
public class User implements Closeable {private final Cleaner cleaner;private final _User user;public User() {user = new _User();cleaner = Cleaner.create(this, user);}@Overridepublic String toString() {return user.toString();}@Overridepublic void close() {cleaner.clean();}@EqualsAndHashCode@ToStringprivate static class _User implements Runnable {private final String id;public _User() {id = IdWorker.get32UUID();}@Overridepublic void run() {System.out.printf("哦不! 我(%s)要被回收了!%n", id);}}
}

三、两个Cleaner！（推荐使用 java.lang.ref.Cleaner + Closeable）

1.使用Cleaner示例（推荐）：

import java.util.concurrent.TimeUnit;public class CleanerTest {public static void main(String[] args) {User user1 = new User();User user2 = new User();System.out.println(user1);System.out.println(user2);System.gc();user1 = user2 = null;System.gc();try { TimeUnit.SECONDS.sleep(3); } catch (InterruptedException e) { throw new RuntimeException(e); }}
}

import com.baomidou.mybatisplus.core.toolkit.IdWorker;
import lombok.EqualsAndHashCode;
import lombok.ToString;import java.lang.ref.Cleaner;@EqualsAndHashCode
public class User {private final String id;private final Cleaner cleaner = Cleaner.create();private final Cleaner.Cleanable cleanable;public User() {this.id = IdWorker.get32UUID();cleanable = cleaner.register(this, new State());}@Overridepublic String toString() {return "User{" +"id='" + id + '\'' +'}';}@EqualsAndHashCode@ToStringprivate static class State implements Runnable {public State() {System.out.println("[构造中...]: 这里一般通过参数获取堆外内存地址等信息。");}@Overridepublic void run() {System.out.println("[回收中...]：这里一般根据堆外内存地址等信息，完成堆外内存释放。");}}
}

↓
官方还推荐将要特定被回收的类实现Closeable接口，用于资源自动回收
↓

import com.baomidou.mybatisplus.core.toolkit.IdWorker;
import lombok.EqualsAndHashCode;
import lombok.ToString;import java.io.Closeable;
import java.lang.ref.Cleaner;@EqualsAndHashCode
public class User implements Closeable {private final String id;private final Cleaner cleaner = Cleaner.create();private final Cleaner.Cleanable cleanable;public User() {this.id = IdWorker.get32UUID();cleanable = cleaner.register(this, new State());}@Overridepublic String toString() {return "User{" +"id='" + id + '\'' +'}';}@Overridepublic void close() {// Cleaner.Cleanablecleanable.clean();}@EqualsAndHashCode@ToStringprivate static class State implements Runnable {public State() {System.out.println("[构造中...]: 这里一般通过参数获取堆外内存地址等信息。");}@Overridepublic void run() {System.out.println("[回收中...]：这里一般根据堆外内存地址等信息，完成堆外内存释放。");}}
}

public class CleanerTest {public static void main(String[] args) {try (User user1 = new User();User user2 = new User();) {System.out.println(user1);System.out.println(user2);}}
}

2. 结果测试