Intermediate and advanced Java interview questions (with answers)

#1. How does redis synchronize with local data?

The program implements mysql updates, additions, and deletions and will operate redis synchronously

The program queries redis. If it does not exist, it queries mysql and automatically saves redis

2. How many data structures does redis have?

set, list, hash, string, zset

3. How is java memory overflow caused?

OutOfMemoryError:

(1)PerGern Space A large number of jars or classes are used in the program, causing insufficient space for the virtual machine to load classes.

Solution: Adjust parameters XX:PermSize and XX:MaxPermSize, reduce jar packages and reduce repeated loading of classes

(2) Java Heap

Space Java virtual machine creation is too Multiple objects. Solution: Adjust parameters Xms (initial heap size) and Xmx (maximum heap size), check for infinite loops or unnecessary creation of duplicate objects.

（3）unable to create new native Thread

The JVM takes up too much memory space, and creating a thread in the JVM requires creating a thread in the operating system. Solution: Adjust the thread size in the JVM.

4. String s = “123”, how many objects are generated by this statement?

If there is no "123" in the string pool, generate one and put it into the constant pool. If there is "123", generate 0

5 , the new features of JDK8, describe with examples

(1) lambda expression: functional programming, method reference

(2) Stream API

(3 ) Default method of the interface

(4) Improvement of date and time API, new DateTimeFormatter method

6. Solve high concurrency and high load

(1) Make HTML as static as possible, use the information entry and release system CMS to automatically generate static pages for information entry, and cache dynamic data that does not change frequently on the front end.

(2) CDN acceleration, distributing resources such as CSS/JS on different servers

(3) Cache data that does not change frequently (Redis, memcache).

(4) The picture server is separated from the application server.

(5) Cluster

7. What is the role of the producer and consumer models?

(1) Improve the operating efficiency of the entire system by balancing production capacity and consumer spending power (2) Decoupling

8, Mybatis Level 1, Level 2 Level cache

(1) Level one cache: HashMap local cache based on PerpetualCache, which stores the scope Session. When Session

flush or close, all Cache in the Session will be cleared.

(2) The second-level cache has the same mechanism as the first-level cache. By default, it also uses PerpetualCache and HashMap storage. The difference is in the storage scope Mapper, and the storage source can be customized. If you need to enable the second-level cache. Add

9 to the sql mapping file to describe the detailed process of a service from publishing to consumption

First obtain the configuration information of zk, and then obtain the URL that needs to be exposed. Then call the registry and register method to register the URL to zookeeper

10. How to achieve load balancing? What algorithms can be achieved?

Random (random), round-robin, consistent-hash and master-slave

11. If you want How do you implement Spring AOP?

The implementation of aop technology is mainly divided into two categories: one is the use of dynamic proxy technology, which uses the method of intercepting messages to decorate the messages to replace the execution of the original object behavior

The second is to use static weaving to introduce specific syntax to create "aspects", so that the code related to "aspects" is woven into the compiler

12. How to prevent repeated page submissions?

Cluster environment: using token plus redis (redis is single-threaded, processing needs to be queued)

Processing process:

1. Before submitting data, you must submit it to the service Apply for a token, put the token into the redis memory, and the token is valid for

2. Verify the token in the background after submission, delete the token at the same time, generate a new token and return

13. What is micro Serve?

Split the project into microservices according to different business rules and deploy them on different machines. Services call each other

14. What is a web service?

(1) A web service is an application that exposes an API that can be called through the web to the outside world

(2) Transmits data based on the HTTP protocol, which makes running Different applications on different machines can exchange data or integrate with each other without resorting to additional, specialized third-party software and hardware

15. Tell me about the reasons for choosing Struts2 for your project?

①Action is a POJO class, does not rely on Servlet API, and has good testability; ②Powerful interceptor simplifies the complexity of development;

③Supports multiple performances Layer technology: JSP, Freemarker, etc.; ④ Flexible verification methods; ⑤ Internationalization (I18N) support ⑥ Declarative exception management;

⑦ Simplify Ajax through JSON plug-in; ⑧ Integrate with Spring through Spring plug-in;

16. Talk about the difference between interceptors and filters?

Both interceptors and filters can be used to implement cross-cutting attention functions. The main differences are: ①Interceptors are based on the JAVA reflection mechanism, while filters are based on function callbacks

②Filters Depends on the Servlet container, while the interceptor does not depend on the Servlet container

③Interceptors can only work on Action requests (methods in Action), while filters can work on almost all requests (CSS JSP JS)

17. What types of transaction management does Spring support?

Programmatic transaction management: Programmatically manage things, great flexibility, difficult to maintain

Declarative transaction management: Business code and transaction management can be separated, and only Use annotations and XML configuration to manage things

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