JAVA9琐碎特性
Java9相关记录
https://gitee.com/bgt0314/java-9
模块化系统运行影像
示例 System.out.println(ClassLoader.getSystemResource("java/lang/Class.class"));
- jdk8执行结果：
jar:file:/D:/BaiduNetdiskDownload/jdk1.8.0_45/jre/lib/rt.jar!/java/lang/Class.class
- jdk9执行结果：
jrt:/java.base/java/lang/Class.class
查看源码发现，jdk9新增了Loader类，并在其中getResource加入了模块化相关的逻辑
@Override
public URL findResource(String name) {
String pn = Resources.toPackageName(name);
LoadedModule module = localPackageToModule.get(pn);
if (module != null) {
try {
URL url = findResource(module.name(), name);
if (url != null
&& (name.endsWith(".class")
|| url.toString().endsWith("/")
|| isOpen(module.mref(), pn))) {
return url;
}
} catch (IOException ioe) {
// ignore
}
} else {
for (ModuleReference mref : nameToModule.values()) {
try {
URL url = findResource(mref.descriptor().name(), name);
if (url != null) return url;
} catch (IOException ioe) {
// ignore
}
}
}
return null;
}
下划线_标识符的改变
在Java8中_是可以作为变量名使用，只不过会警告，在Java9则是错误
-
8
-
9
try-with-resources改善
- 9之前
InputStream inputStream = new FileInputStream("test.txt");
try (InputStream stream = inputStream) {} catch (IOException e) {}InputStream inputStream = new FileInputStream("test.txt");
try (InputStream stream = inputStream) {} catch (IOException e) {}
- 9
InputStream inputStream = new FileInputStream("test.txt");
try (inputStream) {} catch (IOException e) {}
接口支持private方法
示例:
public interface RickyInterface{
public void setUp();
private static void printInterfaceName(){
System.out.println("RickyInterface");
}
public static void displayInterfaceName(){
printInterfaceName();
}
}
匿名内部类的菱形操作符
- Java7是我们可以这样使用<>
List<String> list1 = new ArrayList<String>(); List<String> list2 = new ArrayList<>();
- java9中我们可以对匿名内部类使用
Iterator <String> iter = new Iterator <> () {
@Override
public boolean hasNext() {
return false;
}
@Override
public String next() {
return null;
}
};
Java9中的Flow(生产者消费者)
以下为官方示例
package com.ricky.flow;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.Future;
import java.util.concurrent.Flow.*;
import java.util.function.Consumer;
/**
java9中新增的生产者消费者
以下是官方示例(源码中的用法)
*
*/
public class FlowDemo {
public static void main(String[] args) {
OneShotPublisher publisher=new OneShotPublisher();
SampleSubscriber subscriber=new SampleSubscriber(10, new Consumer() {
@Override
public void accept(Object o) {
if (o instanceof Boolean) {
boolean b= (boolean) o;
if (b) {
System.out.println("开启任务执行");
}
}else {
System.out.println("其他非boolean情况");
}
}
});
publisher.subscribe(subscriber);
publisher.subscribe(subscriber);//验证是否可以多次消费
try {
Thread.currentThread().join(10);//避免执行失败
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
/**
* 一次性生产者
*
* 消息控件-->生产者(发布者)
*/
class OneShotPublisher implements Publisher<Boolean> {
private final ExecutorService executor = ForkJoinPool.commonPool(); // daemon-based
private boolean subscribed; // 首次订阅后变为true 默认false 只能消费一次
/**
* 推送消费者
* @param subscriber
*/
public synchronized void subscribe(Subscriber<? super Boolean> subscriber) {
if (subscribed)
subscriber.onError(new IllegalStateException()); // 只能消费一次
else {
subscribed = true;//这里标示已经消费过了
subscriber.onSubscribe(new OneShotSubscription(subscriber, executor));
}
}
/***
* 消息控件-->链接者
*/
static class OneShotSubscription implements Subscription {
private final Subscriber<? super Boolean> subscriber;
private final ExecutorService executor;
private Future<?> future; // to allow cancellation
private boolean completed;
OneShotSubscription(Subscriber<? super Boolean> subscriber,
ExecutorService executor) {
this.subscriber = subscriber;
this.executor = executor;
}
/**
* 请求执行
* @param n
*/
public synchronized void request(long n) {
System.out.println("请求："+completed);
if (n != 0 && !completed) {
completed = true;
if (n < 0) {
IllegalArgumentException ex = new IllegalArgumentException();
executor.execute(() -> subscriber.onError(ex));
} else {
future = executor.submit(() -> {
subscriber.onNext(Boolean.TRUE);
subscriber.onComplete();
});
}
}
}
/**
* 拒绝
*/
public synchronized void cancel() {
completed = true;
if (future != null) future.cancel(false);
}
}
}
/**
* 简单消费者
*
* 消息控件-->消费者(接收者)
* @param <T>
*/
class SampleSubscriber<T> implements Subscriber<T> {
final Consumer<? super T> consumer;
Subscription subscription;
final long bufferSize;
long count;
SampleSubscriber(long bufferSize, Consumer<? super T> consumer) {
this.bufferSize = bufferSize;
this.consumer = consumer;
}
public void onSubscribe(Subscription subscription) {
long initialRequestSize = bufferSize;
count = bufferSize - bufferSize / 2; // re-request when half consumed
(this.subscription = subscription).request(initialRequestSize);
}
public void onNext(T item) {
if (--count <= 0)
subscription.request(count = bufferSize - bufferSize / 2);
consumer.accept(item);
}
public void onError(Throwable ex) { ex.printStackTrace(); }
public void onComplete() {
System.out.println("hi,ricky bai,your task complete");
}
}
/**
* 自由消费者
* @param <T>
*/
class UnboundedSubscriber<T> implements Subscriber<T> {
public void onSubscribe(Subscription subscription) {
subscription.request(Long.MAX_VALUE); // effectively unbounded
}
public void onNext(T item) { use(item); }
public void onError(Throwable ex) { ex.printStackTrace(); }
public void onComplete() {}
void use(T item) {}
}
JavaDoc
添加搜索功能，并且是html5格式。如下图所示
Deprecated注解 改善
- Java9之前的
package java.lang;
import java.lang.annotation.*;
import static java.lang.annotation.ElementType.*;
/**
* A program element annotated @Deprecated is one that programmers
* are discouraged from using, typically because it is dangerous,
* or because a better alternative exists. Compilers warn when a
* deprecated program element is used or overridden in non-deprecated code.
*
* @author Neal Gafter
* @since 1.5
* @jls 9.6.3.6 @Deprecated
*/
@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target(value={CONSTRUCTOR, FIELD, LOCAL_VARIABLE, METHOD, PACKAGE, PARAMETER, TYPE})
public @interface Deprecated {
}
- Java9
package java.lang;
import java.lang.annotation.*;
import static java.lang.annotation.ElementType.*;
/**
* A program element annotated {@code @Deprecated} is one that programmers
* are discouraged from using. An element may be deprecated for any of several
* reasons, for example, its usage is likely to lead to errors; it may
* be changed incompatibly or removed in a future version; it has been
* superseded by a newer, usually preferable alternative; or it is obsolete.
*
* <p>Compilers issue warnings when a deprecated program element is used or
* overridden in non-deprecated code. Use of the {@code @Deprecated}
* annotation on a local variable declaration or on a parameter declaration
* or a package declaration has no effect on the warnings issued by a compiler.
*
* <p>When a module is deprecated, the use of that module in {@code
* requires}, but not in {@code exports} or {@code opens} clauses causes
* a warning to be issued. A module being deprecated does <em>not</em> cause
* warnings to be issued for uses of types within the module.
*
* <p>This annotation type has a string-valued element {@code since}. The value
* of this element indicates the version in which the annotated program element
* was first deprecated.
*
* <p>This annotation type has a boolean-valued element {@code forRemoval}.
* A value of {@code true} indicates intent to remove the annotated program
* element in a future version. A value of {@code false} indicates that use of
* the annotated program element is discouraged, but at the time the program
* element was annotated, there was no specific intent to remove it.
*
* @apiNote
* It is strongly recommended that the reason for deprecating a program element
* be explained in the documentation, using the {@code @deprecated}
* javadoc tag. The documentation should also suggest and link to a
* recommended replacement API, if applicable. A replacement API often
* has subtly different semantics, so such issues should be discussed as
* well.
*
* <p>It is recommended that a {@code since} value be provided with all newly
* annotated program elements. Note that {@code since} cannot be mandatory,
* as there are many existing annotations that lack this element value.
*
* <p>There is no defined order among annotation elements. As a matter of
* style, the {@code since} element should be placed first.
*
* <p>The {@code @Deprecated} annotation should always be present if
* the {@code @deprecated} javadoc tag is present, and vice-versa.
*
* @author Neal Gafter
* @since 1.5
* @jls 9.6.4.6 @Deprecated
*/
@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target(value={CONSTRUCTOR, FIELD, LOCAL_VARIABLE, METHOD, PACKAGE, MODULE, PARAMETER, TYPE})
public @interface Deprecated {
/**
* Returns the version in which the annotated element became deprecated.
* The version string is in the same format and namespace as the value of
* the {@code @since} javadoc tag. The default value is the empty
* string.
*
* @return the version string
* @since 9
*/
String since() default "";
/**
* Indicates whether the annotated element is subject to removal in a
* future version. The default value is {@code false}.
*
* @return whether the element is subject to removal
* @since 9
*/
boolean forRemoval() default false;
}
ProcessHandle
进程相关API，通过此类可以获取JVM运行线程的相关信息，
- 示例
package com.ricky.processhandle;
public class ProcessHandleDemo {
public static void main(String[] args) {
System.out.println("PID:"+ProcessHandle.current().pid());
System.out.println("info:"+ProcessHandle.current().info());
System.out.println("子进程:"+ProcessHandle.current().children());
System.out.println("是否存活:"+ProcessHandle.current().isAlive());
System.out.println("父进程:"+ProcessHandle.current().parent());
System.out.println("快照:"+ProcessHandle.current().descendants());
}
}
- 执行结果
PID:17540 info:[user: Optional[RICKY\baiguantao], cmd: D:\Program Files\Java\jdk-9\bin\java.exe, startTime: Optional[2017-11-23T09:28:11.459Z], totalTime: Optional[PT0.3276021S]] 子进程:[email protected] 是否存活:true 父进程:Optional[11432] 快照:[email protected]
UTF-8 Property Files
在Java9中，编码从ISO-8859-1转为UTF-8 。
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转载于:https://my.oschina.net/lt0314/blog/1581479