Shulou(Shulou.com)06/01 Report--

This article mainly introduces "what is the thread safety problem of Servlet". In daily operation, I believe that many people have doubts about the thread safety problem of Servlet. The editor consulted all kinds of materials and sorted out simple and easy-to-use operation methods. I hope it will be helpful to answer the doubt of "what is the thread safety problem of Servlet?" Next, please follow the editor to study!

The Servlet architecture is based on the Java multithreading mechanism, and its lifecycle is the responsibility of the Web container.

When a client requests a Servlet for the first time, the Servlet container instantiates the Servlet class based on the web.xml configuration file. When a new client requests the Servlet, the Servlet class is no longer instantiated, that is, multiple threads are using the instance.

In this way, when two or more threads access the same Servlet at the same time, multiple threads may access the same resource at the same time, and the data may become inconsistent, so it is easy to cause a series of security problems.

There are many ways to solve this kind of problem.

1. Implement SingleThreadModel interface

This interface specifies how the system handles calls to the same Servlet. If a Servlet is specified by this interface, then the service method in this Servlet will not be executed by two threads at the same time, and there will certainly be no thread safety issues. This method only needs to inherit the interface.

Public class XXXXX extends HttpServlet implements SingleThreadModel {. }

2. Synchronize operations on shared data

Using the synchronized keyword can ensure that only one thread can access the protected section at a time. In this paper, we can ensure the thread safety of Servlet by synchronizing block operations. The synchronized code is as follows:

Public class XXXXXX extends HttpServlet {. Synchronized (this) {XXXX}}

3. Avoid using instance variables

Some thread safety problems are caused by instance variables, as long as instance variables are not used in any method in the Servlet, then the Servlet is thread safe.

Testing the above three methods shows that thread-safe Servlet programs can be designed with them. However, if a Servlet implements the SingleThreadModel interface, the Servlet engine will create a separate Servlet instance for each new request, which will incur a lot of overhead. SingleThreadModel is no longer advocated in Servlet2.4; similarly, the use of synchronization in programs to protect shared data to be used will greatly degrade the performance of the system. This is because the synchronized block of code can only be executed by one thread at a time, reducing the throughput of processing customer requests at the same time, and many customers are in a blocking state. In addition, in order to ensure the consistency of the main memory content and the data in the working memory of the thread, the cache should be refreshed frequently, which will greatly affect the performance of the system. Therefore, in the actual development, we should also avoid or minimize the synchronization code in Servlet; avoiding the use of instance variables in Serlet is the best choice to ensure servlet thread safety. As you can see from the Java memory model, the temporary variables in the method allocate space on the stack, and each thread has its own private stack space, so they do not affect thread safety.

Summary

Thread safety problems with Servlet only show up with a large number of concurrent visits and are difficult to find, so you should pay special attention to writing Servlet programs. Thread safety problems are mainly caused by instance variables, so you should avoid using instance variables in Servlet. If the application design cannot avoid using instance variables, use synchronization to protect the instance variables to be used, but to ensure the best performance of the system, synchronize the code path with the least availability.

At this point, the study on "what is the thread safety problem of Servlet" is over. I hope to be able to solve your doubts. The collocation of theory and practice can better help you learn, go and try it! If you want to continue to learn more related knowledge, please continue to follow the website, the editor will continue to work hard to bring you more practical articles!

Welcome to subscribe "Shulou Technology Information " to get latest news, interesting things and hot topics in the IT industry, and controls the hottest and latest Internet news, technology news and IT industry trends.