What are the essential differences between CGI and servlet running modes? What are the fundamental differences between PHP and Java in Web development?

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FastCGI is a network protocol that works on a socket and has nothing to do with the language. In general, the previous CGI process is a process from the server fork when every request comes in. it only processes this request and exits after the processing is complete. The process is to obtain the HTTP header from the environment variable, read POST data from standard input and output HTTP response from standard output. Due to the need to constantly create and destroy processes, this implementation method has low performance and many restrictions on functions. FastCGI is an improvement of CGI. it accepts multiple consecutive requests on a single connection and processes them one by one, thus increasing the throughput. FastCGI and CGI are the same as languages. any language can use FastCGI as long as it complies with the FastCGI protocol. However, the processing model of FastCGI is restricted. Generally, only one request can be processed at a single connection, to achieve a certain degree of concurrency, you must create many processes (FastCGI also has the multiplexing function, but does not know how to support it)

However, from the perspective of Web applications, the difference between the two is not big. Although PHP uses FastCGI, it also calls a PHP script for each request. Although many PHP programmers like to mix web pages and code to make it difficult to maintain, PHP also supports the use of OOP, using MVC like Java; java also supports templates such as JSP that can embed code. There are some differences. for example, Java works in the same process, global objects can be called, and additional thread pools can be used, the lifecycle of PHP Objects is basically limited to the scope of a single Request. However, many things are similar and all are Request-oriented programming. Let's start with simple server code.
CGI: View Python's built-in CGIHTTPServer
The main code is as follows. in run_cgi, fork processes run the cgi program again, and the server process is in a parent-child relationship.
Servlet for spring + jetty, Servlet for spring + jetty,
The app code and the server are in the same process The app code and the server are in the same process