正如本文所描述的，Servlet是一种扩展Java服务器并访问其功能的标准化方式。

每个Servlet都可以被视为一个小型服务器(因此得名)，它可以访问用Java代码建模的请求和响应，以及其他上下文数据，比如Session。

有了这些，servlet的Java代码就可以与它所需要的任何东西交互以呈现响应，包括交给JSP页面来生成HTML视图。

除了以上，只是要指出流血的明显……

To many this is hyper obvious, but to someone used to writing apps which are just run and then end: a servlet spends most of its time hanging around doing nothing... waiting to be sent something, a request, and then responding to it. For this reason a servlet has a lifetime: it is initalised and then waits around, responding to anything thrown at it, and is then destroyed. Which implies that it has to be created (and later destroyed) by something else (a framework), that it runs in its own thread or process, and that it does nothing unless asked to. And also that, by some means or other, a mechanism must be implemented whereby this "entity" can "listen" for requests.

我建议阅读有关线程、进程和套接字的内容可以让你对此有所了解:这与一个基本的“hello world”应用程序的功能方式是完全不同的。

有人可能会说，术语“服务器”或“servlet”有点大材小用。一个更合理、更简单的名字可能是“responder”。选择术语“服务器”的原因是历史的:第一个这样的安排是“文件服务器”，多个用户/客户端终端将从中央机器请求特定的文件，然后该文件将像一本书或一盘炸鱼和薯条一样被“提供”。

如果你是初学者，我认为本教程可能会给出什么是Servlet的基本概念…

以下是一些有价值的观点。

利用Servlet技术创建web应用程序，该应用程序驻留在服务器端，生成动态网页。

Servlet可以根据上下文以多种方式描述。

Servlet是一种用于创建web应用程序的技术。 Servlet是一个API，它提供了许多接口和类，包括 文件。 Servlet是一个必须实现的接口，用于创建任何 servlet。 Servlet是一个扩展服务器和服务器功能的类 响应传入的请求。它可以对任何类型的 请求。 Servlet是部署在服务器上用于创建的web组件 动态网页。 参考:在这里。

A servlet at its very core is a java class; which can handle HTTP requests. Typically the internal nitty-gritty of reading a HTTP request and response over the wire is taken care of by the containers like Tomcat. This is done so that as a server side developer you can focus on what to do with the HTTP request and responses and not bother about dealing with code that deals with networking etc. The container will take care of things like wrapping the whole thing in a HTTP response object and send it over to the client (say a browser).

Now the next logical question to ask is who decides what is a container supposed to do? And the answer is; In Java world at least It is guided (note I did not use the word controlled) by specifications. For example Servlet specifications (See resource 2) dictates what a servlet must be able to do. So if you can write an implementation for the specification, congratulations you just created a container (Technically containers like Tomcat also implement other specifications and do tricky stuff like custom class loaders etc but you get the idea).

假设您有一个容器，您的servlet现在是java类，其生命周期将由容器维护，但它们对传入HTTP请求的反应将由您决定。你可以通过在init()、doGet()、doPost()等预定义方法中编写你想要做的事情来做到这一点。看看资源3。

这里有一个有趣的练习。像资源3中那样创建一个简单的servlet，在它的构造函数方法(是的，你可以有一个servlet的构造函数)、init()、doGet()、doPost()方法中编写一些System.out.println()语句，并在tomcat中运行servlet。查看控制台日志和tomcat日志。

资源

看看这里的HTTP servlet (Tomcat示例)。 Servlet规范。 简单的Servlet示例。 开始在线阅读这本书/PDF 它还提供了整本书的下载。也许这会有帮助。 如果你刚刚开始使用servlet，那么阅读相关材料和servlet API是一个不错的主意。这是一个较慢的学习过程，但对弄清基本知识更有帮助。

Servlet是web应用程序中用来创建动态网页的服务器端技术。servlet实际上是一个api，它由一组类和接口组成，具有一定的功能。当我们使用Servlet API时，我们可以使用Servlet类和接口的预定义功能。

Servlet的生命周期:

Web容器维护servlet实例的生命周期。

1。加载Servlet类

２ ． 创建Servlet实例

3.Init()方法被调用

4所示。调用Service()方法

５ ． 调用Destroy()方法

当客户端(浏览器)提出请求时，web-container检查servlet是否正在运行，如果是，则调用service()方法并向浏览器提供响应。

当servlet没有运行时，web-container遵循以下步骤。

1. Classloader装入servlet类

2. 实例化servlet

3.初始化servlet

4.调用service()方法

服务请求后，web-container等待特定的时间，在这段时间内，如果请求来了，那么它只调用service()方法，否则它调用destroy()方法。

什么是Servlet?

A servlet is simply a class which responds to a particular type of network request - most commonly an HTTP request. Basically servlets are usually used to implement web applications - but there are also various frameworks which operate on top of servlets (e.g. Struts) to give a higher-level abstraction than the "here's an HTTP request, write to this HTTP response" level which servlets provide. Servlets run in a servlet container which handles the networking side (e.g. parsing an HTTP request, connection handling etc). One of the best-known open source servlet containers is Tomcat. In a request/response paradigm, a web server can serve only static pages to the client To serve dynamic pages, a we require Servlets. Servlet is nothing but a Java program This Java program doesn’t have a main method. It only has some callback methods. How does the web server communicate to the servlet? Via container or Servlet engine. Servlet lives and dies within a web container. Web container is responsible for invoking methods in a servlets. It knows what callback methods the Servlet has.

请求流程

Client sends HTTP request to Web server Web server forwards that HTTP request to web container. Since Servlet can not understand HTTP, its a Java program, it only understands objects, so web container converts that request into valid request object Web container spins a thread for each request All the business logic goes inside doGet() or doPost() callback methods inside the servlets Servlet builds a Java response object and sends it to the container. It converts that to HTTP response again to send it to the client

容器如何知道哪个Servlet客户端请求了?

有一个文件叫web。xml 这是web容器的主文件 在这个文件中有关于servlet的信息- servlet Servlet-name servlet类 servlet-mappings-类似/Login或/Notifications的路径映射在这里 Servlet-name url模式 等等 web应用程序中的每个servlet都应该在这个文件中有一个条目 查找的方式是- url-pattern -> servlet-name -> servlet-class

如何“安装”servlet ? servlet对象继承自javax.servlet库。*。Tomcat和Spring可以用来利用这些对象来适应用例。

参考-在1.5x上观看- https://www.youtube.com/watch?v=tkFRGdUgCsE。这有一个很棒的解释。