What's New in JDK 8
Java Platform, Standard Edition 8 is a major feature release. This document summarizes features and enhancements in Java SE 8 and in JDK 8, Oracle's implementation of Java SE 8. Click the component name for a more detailed description of the enhancements for that component.
Java Programming Language
Lambda Expressions（lambda表达）, a new language feature, has been introduced in this release. They enable you to treat functionality as a method argument, or code as data. Lambda expressions let you express instances of single-method interfaces (referred to as functional interfaces) more compactly.
Method references provide easy-to-read lambda expressions for methods that already have a name.
Default methods enable new functionality to be added to the interfaces of libraries and ensure binary compatibility with code written for older versions of those interfaces.
Repeating Annotations provide the ability to apply the same annotation type more than once to the same declaration or type use.
Type Annotations provide the ability to apply an annotation anywhere a type is used, not just on a declaration. Used with a pluggable type system, this feature enables improved type checking of your code.
Improved type inference.
Method parameter reflection.
Collections
Classes in the new java.util.stream package provide a Stream API to support functional-style operations on streams of elements. The Stream API is integrated into the Collections API, which enables bulk operations on collections, such as sequential or parallel map-reduce transformations.
Performance Improvement for HashMaps with Key Collisions
Compact Profiles contain predefined subsets of the Java SE platform and enable applications that do not require the entire Platform to be deployed and run on small devices.
Security
Client-side TLS 1.2 enabled by default
New variant of AccessController.doPrivileged that enables code to assert a subset of its privileges, without preventing the full traversal of the stack to check for other permissions
Stronger algorithms for password-based encryption
SSL/TLS Server Name Indication (SNI) Extension support in JSSE Server
Support for AEAD algorithms: The SunJCE provider is enhanced to support AES/GCM/NoPadding cipher implementation as well as GCM algorithm parameters. And the SunJSSE provider is enhanced to support AEAD mode based cipher suites. See Oracle Providers Documentation, JEP 115.
KeyStore enhancements, including the new Domain KeyStore type java.security.DomainLoadStoreParameter, and the new command option -importpassword for the keytool utility
SHA-224 Message Digests
Enhanced Support for NSA Suite B Cryptography
Better Support for High Entropy Random Number Generation
New java.security.cert.PKIXRevocationChecker class for configuring revocation checking of X.509 certificates
64-bit PKCS11 for Windows
New rcache Types in Kerberos 5 Replay Caching
Support for Kerberos 5 Protocol Transition and Constrained Delegation
Kerberos 5 weak encryption types disabled by default
Unbound SASL for the GSS-API/Kerberos 5 mechanism
SASL service for multiple host names
JNI bridge to native JGSS on Mac OS X
Support for stronger strength ephemeral DH keys in the SunJSSE provider
Support for server-side cipher suites preference customization in JSSE
JavaFX
The new Modena theme has been implemented in this release. For more information, see the blog at fxexperience.com.
The new SwingNode class enables developers to embed Swing content into JavaFX applications. See the SwingNode javadoc and Embedding Swing Content in JavaFX Applications.
The new UI Controls include the DatePicker and the TreeTableView controls.
The javafx.print package provides the public classes for the JavaFX Printing API. See the javadoc for more information.
The 3D Graphics features now include 3D shapes, camera, lights, subscene, material, picking, and antialiasing. The new Shape3D (Box, Cylinder, MeshView, and Sphere subclasses), SubScene, Material, PickResult, LightBase (AmbientLight and PointLight subclasses) , and SceneAntialiasing API classes have been added to the JavaFX 3D Graphics library. The Camera API class has also been updated in this release. See the corresponding class javadoc for javafx.scene.shape.Shape3D, javafx.scene.SubScene, javafx.scene.paint.Material, javafx.scene.input.PickResult, javafx.scene.SceneAntialiasing, and the Getting Started with JavaFX 3D Graphics document.
The WebView class provides new features and improvements. Review Supported Features of HTML5 for more information about additional HTML5 features including Web Sockets, Web Workers, and Web Fonts.
Enhanced text support including bi-directional text and complex text scripts such as Thai and Hindi in controls, and multi-line, multi-style text in text nodes.
Support for Hi-DPI displays has been added in this release.
The CSS Styleable* classes became public API. See the javafx.css javadoc for more information.
The new ScheduledService class allows to automatically restart the service.
JavaFX is now available for ARM platforms. JDK for ARM includes the base, graphics and controls components of JavaFX.
Tools
The jjs command is provided to invoke the Nashorn engine.
The java command launches JavaFX applications.
The java man page has been reworked.
The jdeps command-line tool is provided for analyzing class files.
Java Management Extensions (JMX) provide remote access to diagnostic commands.
The jarsigner tool has an option for requesting a signed time stamp from a Time Stamping Authority (TSA).
Javac tool
The -parameters option of the javac command can be used to store formal parameter names and enable the Reflection API to retrieve formal parameter names.
The type rules for equality operators in the Java Language Specification (JLS) Section 15.21 are now correctly enforced by the javac command.
The javac tool now has support for checking the content of javadoc comments for issues that could lead to various problems, such as invalid HTML or accessibility issues, in the files that are generated when javadoc is run. The feature is enabled by the new -Xdoclint option. For more details, see the output from running "javac -X". This feature is also available in the javadoc tool, and is enabled there by default.
The javac tool now provides the ability to generate native headers, as needed. This removes the need to run the javah tool as a separate step in the build pipeline. The feature is enabled in javac by using the new -h option, which is used to specify a directory in which the header files should be written. Header files will be generated for any class which has either native methods, or constant fields annotated with a new annotation of type java.lang.annotation.Native.
Javadoc tool
The javadoc tool supports the new DocTree API that enables you to traverse Javadoc comments as abstract syntax trees.
The javadoc tool supports the new Javadoc Access API that enables you to invoke the Javadoc tool directly from a Java application, without executing a new process. See the javadoc what's new page for more information.
The javadoc tool now has support for checking the content of javadoc comments for issues that could lead to various problems, such as invalid HTML or accessibility issues, in the files that are generated when javadoc is run. The feature is enabled by default, and can also be controlled by the new -Xdoclint option. For more details, see the output from running "javadoc -X". This feature is also available in the javac tool, although it is not enabled by default there.
Internationalization
Unicode Enhancements, including support for Unicode 6.2.0
Adoption of Unicode CLDR Data and the java.locale.providers System Property
New Calendar and Locale APIs
Ability to Install a Custom Resource Bundle as an Extension
Deployment
For sandbox applets and Java Web Start applications, URLPermission is now used to allow connections back to the server from which they were started. SocketPermission is no longer granted.
The Permissions attribute is required in the JAR file manifest of the main JAR file at all security levels.
Date-Time Package - a new set of packages that provide a comprehensive date-time model.
Scripting
Nashorn Javascript Engine
Pack200
Pack200 Support for Constant Pool Entries and New Bytecodes Introduced by JSR 292
JDK8 support for class files changes specified by JSR-292, JSR-308 and JSR-335
IO and NIO
New SelectorProvider implementation for Solaris based on the Solaris event port mechanism. To use, run with the system property java.nio.channels.spi.Selector set to the value sun.nio.ch.EventPortSelectorProvider.
Decrease in the size of the <JDK_HOME>/jre/lib/charsets.jar file
Performance improvement for the java.lang.String(byte[], *) constructor and the java.lang.String.getBytes() method.
java.lang and java.util Packages
Parallel Array Sorting
Standard Encoding and Decoding Base64
Unsigned Arithmetic Support
JDBC
The JDBC-ODBC Bridge has been removed.
JDBC 4.2 introduces new features.
Java DB
JDK 8 includes Java DB 10.10.
Networking
The class java.net.URLPermission has been added.
In the class java.net.HttpURLConnection, if a security manager is installed, calls that request to open a connection require permission.
Concurrency
Classes and interfaces have been added to the java.util.concurrent package.
Methods have been added to the java.util.concurrent.ConcurrentHashMap class to support aggregate operations based on the newly added streams facility and lambda expressions.
Classes have been added to the java.util.concurrent.atomic package to support scalable updatable variables.
Methods have been added to the java.util.concurrent.ForkJoinPool class to support a common pool.
The java.util.concurrent.locks.StampedLock class has been added to provide a capability-based lock with three modes for controlling read/write access.
Java XML - JAXP
HotSpot
Hardware intrinsics were added to use Advanced Encryption Standard (AES). The UseAES and UseAESIntrinsics flags are available to enable the hardware-based AES intrinsics for Intel hardware. The hardware must be 2010 or newer Westmere hardware. For example, to enable hardware AES, use the following flags:
-XX:+UseAES -XX:+UseAESIntrinsics
To disable hardware AES use the following flags:
-XX:-UseAES -XX:-UseAESIntrinsics
Removal of PermGen.
Default Methods in the Java Programming Language are supported by the byte code instructions for method invocation.
Java Mission Control 5.3 Release Notes
JDK 8 includes Java Mission Control 5.3.
“Java is still not dead—and people are starting to figure that out.”
本教程将用带注释的简单代码来描述新特性，你将看不到大片吓人的文字。
一、接口的默认方法
Java 8允许我们给接口添加一个非抽象的方法实现，只需要使用 default关键字即可，这个特征又叫做扩展方法
二、Lambda 表达式
三、函数式接口
Lambda 表达式是如何在java的类型系统中表示的呢？每一个lambda表达式都对应一个类型，通常是接口类型。而“函数式接口”是指仅仅只包含一个抽象方法的 接口，每一个该类型的lambda表达式都会被匹配到这个抽象方法。因为 默认方法 不算抽象方法，所以你也可以给你的函数式接口添加默认方法。
我们可以将lambda表达式当作任意只包含一个抽象方法的接口类型，确保你的接口一定达到这个要求，你只需要给你的接口添加 @FunctionalInterface 注解，编译器如果发现你标注了这个注解的接口有多于一个抽象方法的时候会报错的。
四、方法与构造函数引用
前一节中的代码还可以通过静态方法引用来表示：Java 8 允许你使用 :: 关键字来传递方法或者构造函数引用，上面的代码展示了如何引用一个静态方法，我们也可以引用一个对象的方法：
五、Lambda 作用域
在lambda表达式中访问外层作用域和老版本的匿名对象中的方式很相似。你可以直接访问标记了final的外层局部变量，或者实例的字段以及静态变量。
六、访问局部变量
我们可以直接在lambda表达式中访问外层的局部变量：
代码如下:
final int num = 1;
Converter<Integer, String> stringConverter =
(from) -> String.valueOf(from + num);
stringConverter.convert(2); // 3
但是和匿名对象不同的是，这里的变量num可以不用声明为final，该代码同样正确：
不过这里的num必须不可被后面的代码修改（即隐性的具有final的语义）
七、访问对象字段与静态变量
和本地变量不同的是，lambda内部对于实例的字段以及静态变量是即可读又可写
八、访问接口的默认方法
还记得第一节中的formula例子么，接口Formula定义了一个默认方法sqrt可以直接被formula的实例包括匿名对象访问到，但是在lambda表达式中这个是不行的。
Lambda表达式中是无法访问到默认方法的，以下代码将无法编译：
JDK 1.8 API包含了很多内建的函数式接口，在老Java中常用到的比如Comparator或者Runnable接口，这些接口都增加了@FunctionalInterface注解以便能用在lambda上。
Java 8 API同样还提供了很多全新的函数式接口来让工作更加方便，有一些接口是来自Google Guava库里的，即便你对这些很熟悉了，还是有必要看看这些是如何扩展到lambda上使用的。
Predicate接口
Predicate 接口只有一个参数，返回boolean类型。该接口包含多种默认方法来将Predicate组合成其他复杂的逻辑（比如：与，或，非）：
Function 接口
Function 接口有一个参数并且返回一个结果，并附带了一些可以和其他函数组合的默认方法（compose, andThen）：
Supplier 接口
Supplier 接口返回一个任意范型的值，和Function接口不同的是该接口没有任何参数
Consumer 接口
Consumer 接口表示执行在单个参数上的操作。
Comparator 接口
Comparator 是老Java中的经典接口， Java 8在此之上添加了多种默认方法：
Optional 接口
Optional 不是函数是接口，这是个用来防止NullPointerException异常的辅助类型，这是下一届中将要用到的重要概念，现在先简单的看看这个接口能干什么：
Optional 被定义为一个简单的容器，其值可能是null或者不是null。在Java 8之前一般某个函数应该返回非空对象但是偶尔却可能返回了null，而在Java 8中，不推荐你返回null而是返回Optional。
Stream 接口
java.util.Stream 表示能应用在一组元素上一次执行的操作序列。Stream 操作分为中间操作或者最终操作两种，最终操作返回一特定类型的计算结果，而中间操作返回Stream本身，这样你就可以将多个操作依次串起来。 Stream 的创建需要指定一个数据源，比如 java.util.Collection的子类，List或者Set， Map不支持。Stream的操作可以串行执行或者并行执行。
Java 8扩展了集合类，可以通过 Collection.stream() 或者 Collection.parallelStream() 来创建一个Stream。下面几节将详细解释常用的Stream操作：
Filter 过滤
过滤通过一个predicate接口来过滤并只保留符合条件的元素，该操作属于中间操作，所以我们可以在过滤后的结果来应用其他Stream操作 （比如forEach）。forEach需要一个函数来对过滤后的元素依次执行。forEach是一个最终操作，所以我们不能在forEach之后来执行 其他Stream操作。
Sort 排序
排序是一个中间操作，返回的是排序好后的Stream。如果你不指定一个自定义的Comparator则会使用默认排序。
需要注意的是，排序只创建了一个排列好后的Stream，而不会影响原有的数据源，排序之后原数据stringCollection是不会被修改的：
Map 映射
中间操作map会将元素根据指定的Function接口来依次将元素转成另外的对象，下面的示例展示了将字符串转换为大写字符串。你也可以通过map来讲对象转换成其他类型，map返回的Stream类型是根据你map传递进去的函数的返回值决定的。
Match 匹配
Stream提供了多种匹配操作，允许检测指定的Predicate是否匹配整个Stream。所有的匹配操作都是最终操作，并返回一个boolean类型的值。
Count 计数
计数是一个最终操作，返回Stream中元素的个数，返回值类型是long。
Reduce 规约
这是一个最终操作，允许通过指定的函数来讲stream中的多个元素规约为一个元素，规越后的结果是通过Optional接口表示的：
并行Streams
前面提到过Stream有串行和并行两种，串行Stream上的操作是在一个线程中依次完成，而并行Stream则是在多个线程上同时执行。
串行排序：
代码如下:
long t0 = System.nanoTime();
long count = values.stream().sorted().count();
System.out.println(count);
long t1 = System.nanoTime();
long millis = TimeUnit.NANOSECONDS.toMillis(t1 - t0);
System.out.println(String.format("sequential sort took: %d ms", millis));
// 串行耗时: 899 ms
并行排序：
代码如下:
long t0 = System.nanoTime();
long count = values.parallelStream().sorted().count();
System.out.println(count);
long t1 = System.nanoTime();
long millis = TimeUnit.NANOSECONDS.toMillis(t1 - t0);
System.out.println(String.format("parallel sort took: %d ms", millis));
// 并行排序耗时: 472 ms
上面两个代码几乎是一样的，但是并行版的快了50%之多，唯一需要做的改动就是将stream()改为parallelStream()。
Map
前面提到过，Map类型不支持stream，不过Map提供了一些新的有用的方法来处理一些日常任务。
Merge做的事情是如果键名不存在则插入，否则则对原键对应的值做合并操作并重新插入到map中。
九、Date API
Java 8 在包java.time下包含了一组全新的时间日期API。新的日期API和开源的Joda-Time库差不多，但又不完全一样，下面的例子展示了这组新API里最重要的一些部分：
Clock 时钟
Clock类提供了访问当前日期和时间的方法，Clock是时区敏感的，可以用来取代 System.currentTimeMillis() 来获取当前的微秒数。某一个特定的时间点也可以使用Instant类来表示，Instant类也可以用来创建老的java.util.Date对象。
Timezones 时区
在新API中时区使用ZoneId来表示。时区可以很方便的使用静态方法of来获取到。 时区定义了到UTS时间的时间差，在Instant时间点对象到本地日期对象之间转换的时候是极其重要的。
LocalTime 本地时间
LocalTime 定义了一个没有时区信息的时间，例如 晚上10点，或者 17:30:15。下面的例子使用前面代码创建的时区创建了两个本地时间。之后比较时间并以小时和分钟为单位计算两个时间的时间差：
LocalDate 本地日期
LocalDate 表示了一个确切的日期，比如 2014-03-11。该对象值是不可变的，用起来和LocalTime基本一致。下面的例子展示了如何给Date对象加减天/月/年。另外要注意的是这些对象是不可变的，操作返回的总是一个新实例。
LocalDateTime 本地日期时间
LocalDateTime 同时表示了时间和日期，相当于前两节内容合并到一个对象上了。LocalDateTime和LocalTime还有LocalDate一样，都是不可变的。LocalDateTime提供了一些能访问具体字段的方法。
和java.text.NumberFormat不一样的是新版的DateTimeFormatter是不可变的，所以它是线程安全的。
关于时间日期格式的详细信息：http://download.java.net/jdk8/docs/api/java/time/format/DateTimeFormatter.html
十、Annotation 注解
在Java 8中支持多重注解了，先看个例子来理解一下是什么意思。
首先定义一个包装类Hints注解用来放置一组具体的Hint注解：
Java 8允许我们把同一个类型的注解使用多次，只需要给该注解标注一下@Repeatable即可。
例 1: 使用包装类当容器来存多个注解（老方法）
代码如下:
@Hints({@Hint("hint1"), @Hint("hint2")})
class Person {}
例 2：使用多重注解（新方法）
代码如下:
@Hint("hint1")
@Hint("hint2")
class Person {}
第二个例子里java编译器会隐性的帮你定义好@Hints注解，了解这一点有助于你用反射来获取这些信息：
代码如下:
Hint hint = Person.class.getAnnotation(Hint.class);
System.out.println(hint); // null
Hints hints1 = Person.class.getAnnotation(Hints.class);
System.out.println(hints1.value().length); // 2
Hint[] hints2 = Person.class.getAnnotationsByType(Hint.class);
System.out.println(hints2.length); // 2
即便我们没有在Person类上定义@Hints注解，我们还是可以通过 getAnnotation(Hints.class) 来获取 @Hints注解，更加方便的方法是使用 getAnnotationsByType 可以直接获取到所有的@Hint注解。
另外Java 8的注解还增加到两种新的target上了：
@Target({ElementType.TYPE_PARAMETER, ElementType.TYPE_USE})
@interface MyAnnotation {}
JDK 1.8里还有很多很有用的东西，比如Arrays.parallelSort, StampedLock和CompletableFuture等等。