Spring WebFlux： Reactive Web（non-blocking servers in general）
Spring Web MVC：传统Servlet Web（servlet applications in general）
[线程：main] Observable 添加观察者！ [线程：main] 通知所有观察者！ [线程：main] 3. 收到数据更新：Hello World [线程：main] 2. 收到数据更新：Hello World [线程：main] 1. 收到数据更新：Hello World
[线程：main] 启动一个JFrame窗口！ [线程：AWT-EventQueue-0] 销毁当前窗口！ [线程：AWT-EventQueue-0] 窗口被关闭，退出程序！
Reactive Programming：响应式编程，异步非阻塞就是响应式编程(Reactive Programming)，与之相对应的是命令式编程。
Reactive并不是一种新的技术，不用Reactive照样可以实现非阻塞（同步、异步均可，推拉模式的结合），比如利用观察者模式实现（比如Java Swing GUI技术）。
reactive programming is a declarative
programming paradigm concerned with
data streams and the propagation of change. With this paradigm it is possible to express static (e.g., arrays) or dynamic (e.g., event emitters)
data streams with ease, and also communicate that an inferred dependency within the associated
execution model exists, which facilitates the automatic propagation of the changed data flow
Reactive Streams JVM实现：https://github.com/reactive-s…
Handling streams of data—especially “live” data whose volume is not predetermined—requires special care in an asynchronous system. The most prominent issue is that resource consumption needs to be carefully controlled such that a fast data source does not overwhelm the stream destination. Asynchrony is needed in order to enable the parallel use of computing resources, on collaborating network hosts or multiple CPU cores within a single machine.
- data source（数据上游），stream destination（数据下游）
In summary, Reactive Streams is a standard and specification for Stream-oriented libraries for the JVM that
- process a potentially unbounded number of elements
- in sequence,
- asynchronously passing elements between components,
- with mandatory non-blocking backpressure.
ReactiveX is a library for composing asynchronous and event-based programs by using observable sequences.
It extends the observer pattern to support sequences of data and/or events and adds operators that allow you to compose sequences together declaratively while abstracting away concerns about things like low-level threading, synchronization, thread-safety, concurrent data structures, and non-blocking I/O.
可观察的数据/事件序列（sequences of data and/or events）
- 数据结构上说：支持数据序列（sequences of data），其实就是数据流（streams of data），并且需要屏蔽高并发相关（线程，同步，线程安全，并发数据结构，非阻塞I/O等）
You can think of the Observable class as a “push” equivalent to
Iterable, which is a “pull.” With an Iterable, the consumer pulls values from the producer and the thread blocks until those values arrive.
- Iterable：For Each语句的提升
- Iterator：迭代器（Java 5）
Reactor is a fully non-blocking reactive programming foundation for the JVM, with efficient demand management (in the form of managing “backpressure”). It integrates directly with the Java 8 functional APIs, notably
Duration. It offers composable asynchronous sequence APIs
Flux(for [N] elements) and
Mono(for [0|1] elements), extensively implementing the
Reactive Streams specification.
Reactor also supports non-blocking inter-process communication with the
reactor-nettyproject. Suited for Microservices Architecture, Reactor Netty offers backpressure-ready network engines for HTTP (including Websockets), TCP, and UDP. Reactive Encoding and Decoding are fully supported.
1.3 Spring WebFlux
The original web framework included in the Spring Framework, Spring Web MVC, was purpose-built for the Servlet API and Servlet containers. The reactive-stack web framework, Spring WebFlux, was added later in version 5.0. It is fully non-blocking, supports
Reactive Streams back pressure, and runs on such servers as Netty, Undertow, and Servlet 3.1+ containers.
- 可以运行在Netty，Undertow，Servlet 3.1+等容器中
- Servlet 3.1也有异步处理
1.3.1 Why WebFlux？
Part of the answer is the need for a non-blocking web stack to handle concurrency with a small number of threads and scale with fewer hardware resources. Servlet 3.1 did provide an API for non-blocking I/O. However, using it leads away from the rest of the Servlet API, where contracts are synchronous (
Servlet) or blocking (
getPart). This was the motivation for a new common API to serve as a foundation across any non-blocking runtime. That is important because of servers (such as Netty) that are well-established in the async, non-blocking space.
The other part of the answer is functional programming. Much as the addition of annotations in Java 5 created opportunities (such as annotated REST controllers or unit tests), the addition of lambda expressions in Java 8 created opportunities for functional APIs in Java. This is a boon for non-blocking applications and continuation-style APIs (as popularized by
CompletableFutureand ReactiveX) that allow declarative composition of asynchronous logic. At the programming-model level, Java 8 enabled Spring WebFlux to offer functional web endpoints alongside annotated controllers.
- 异步非阻塞（non-blocking web stack）
- 少量线程数处理并发性（handle concurrency with a small number of threads）
- 少量硬件资源提高伸缩性（scale with fewer hardware resources.）
- Servlet 3.1 提供一个非阻塞API
- 函数式编程（functional programming）
1.3.2 Define “Reactive”
The term, “reactive,” refers to programming models that are built around reacting to change — network components reacting to I/O events, UI controllers reacting to mouse events, and others. In that sense, non-blocking is reactive, because, instead of being blocked, we are now in the mode of reacting to notifications as operations complete or data becomes available.
There is also another important mechanism that we on the Spring team associate with “reactive” and that is non-blocking back pressure. In synchronous, imperative code, blocking calls serve as a natural form of back pressure that forces the caller to wait. In non-blocking code, it becomes important to control the rate of events so that a fast producer does not overwhelm its destination.
Reactive Streams is a small spec (also adopted in Java 9) that defines the interaction between asynchronous components with back pressure. For example a data repository (acting as Publisher) can produce data that an HTTP server (acting as Subscriber) can then write to the response. The main purpose of Reactive Streams is to let the subscriber to control how quickly or how slowly the publisher produces data.
- 对I / O事件做出反应的网络组件
- 非阻塞在某种程度上说就是Reactive（In that sense, non-blocking is reactive）
Performance has many characteristics and meanings. Reactive and non-blocking generally do not make applications run faster. They can, in some cases, (for example, if using the
WebClientto execute remote calls in parallel). On the whole, it requires more work to do things the non-blocking way and that can increase slightly the required processing time.
The key expected benefit of reactive and non-blocking is the ability to scale with a small, fixed number of threads and less memory. That makes applications more resilient under load, because they scale in a more predictable way. In order to observe those benefits, however, you need to have some latency (including a mix of slow and unpredictable network I/O). That is where the reactive stack begins to show its strengths, and the differences can be dramatic.
- 一般而言，并不是为了使应用程序运行更快（Reactive and non-blocking generally do not make applications run faster）
- 为了非阻塞需要额外的工作可能会增加处理时间（it requires more work to do things the non-blocking way and that can increase slightly the required processing time）
关键的一个好处（The key expected benefit）
- 利用固定、少量的线程，小的内存提供伸缩性的能力（reactive and non-blocking is the ability to scale with a small, fixed number of threads and less memory）
- 可能有背压（back pressure）
Callbacks are hard to compose together, quickly leading to code that is difficult to read and maintain (known as “Callback Hell”).
The second approach (mentioned earlier), seeking more efficiency, can be a solution to the resource wasting problem. By writing asynchronous, non-blocking code, you let the execution switch to another active task using the same underlying resources and later come back to the current process when the asynchronous processing has finished.
But how can you produce asynchronous code on the JVM? Java offers two models of asynchronous programming:
- Callbacks: Asynchronous methods do not have a return value but take an extra
callbackparameter (a lambda or anonymous class) that gets called when the result is available. A well known example is Swing’s
- Futures: Asynchronous methods return a
Future<T>immediately. The asynchronous process computes a
Tvalue, but the
Futureobject wraps access to it. The value is not immediately available, and the object can be polled until the value is available. For instance,
Long Live模式：Netty I/O连接（RPC）
Reactive 性能测试： https://blog.ippon.tech/sprin…
Web：快速响应（Socket Connection Timeout）
Tomcat Connector Thread Pool（200个线程） –> Reactive Thread Pool(50个线程)
- Tomcat Thread 负责处理连接（可以由200个连接扩充到2000个连接）
4. 设计Reactive Web
利用Servlet 3.1规范中的异步处理（Asynchronous processing），异步上下文（AsyncContext）实现异步Servlet。
Some times a filter and/or servlet is unableto complete the processing of a request
without waiting for a resource or event before generating a response. For example, a
servlet may need to wait for an available JDBC connection, for a response from a
remote web service, for a JMS message, or for an application event, before
proceeding to generate a response. Waiting within the servlet is an inefficient
operation as it is a blocking operation that consumes a thread and other limited
resources. Frequently a slow resource such as a database may have many threads
blocked waiting for access and can cause thread starvation and poor quality of
service for an entire web container.
The asynchronous processing of requests is introduced to allow the thread may
return to the container and perform other tasks. When asynchronous processing
begins on the request, another thread or callback may either generate the response
and call completeor dispatch the request so that it may run in the context of the
container using the AsyncContext.dispatchmethod. A typical sequence of events
for asynchronous processing is:
- The request is received and passed via normal filters for authentication etc. to the
- The servlet processes the request parameters and/or content to determine the
nature of the request.
- The servlet issues requests for resources or data, for example, sends a remote web
service request or joins a queue waiting for a JDBC connection.
- The servlet returns without generating a response.
- After some time, the requested resourcebecomes available, the thread handling
that event continues processing either in the same thread or by dispatching to a
resource in the container using the AsyncContext.
利用Servlet 3.1规范中的Non Blocking IO
Non-blocking request processing in the Web Container helps improve the ever
increasing demand for improved Web Container scalability, increase the number of
connections that can simultaneously be handled by the Web Container. Nonblocking IO in the Servlet container allowsdevelopers to readdata as it becomes
available or write data when possible to do so. Non-blocking IO only works with
async request processing in Servlets and Filters (as defined in Section 220.127.116.11,
“Asynchronous processing” on page 2-10), and upgrade processing (as defined in
Section 18.104.22.168, “Upgrade Processing” on page 2-20). Otherwise, an
IllegalStateExceptionmust be thrown when
5. 实现Reactive Web