dreaife的休憩小栈

Manually declaring thread pools with ThreadPoolExecutor helps avoid OOM risks, and monitoring thread pool status is recommended, with different businesses using different thread pools. Thread pool parameters should be configured reasonably to avoid repeated creation and long-running tasks, and thread pools should be named to make troubleshooting easier. Pay attention to issues caused by sharing thread pools with ThreadLocal, and consider using TransmittableThreadLocal to solve context propagation problems.

The Java Memory Model (JMM) defines the visibility of shared variables in multithreaded environments and involves the CPU cache model and instruction reordering. By specifying the relationship between threads and main memory, JMM ensures the visibility and consistency of shared variables and addresses key problems in multithreaded programming. Key concepts include the happens-before principle, atomicity, visibility, and ordering, which help ensure correct program execution in concurrent environments.

This article introduces the basics of Java concurrent programming, including the definitions of threads and processes, Java thread implementation mechanisms, thread life cycle, the differences between concurrency and parallelism, the concepts of synchronous and asynchronous execution, and the advantages and disadvantages of multithreading. It also discusses thread safety, deadlocks and how to avoid them, the use of the volatile keyword, the difference between optimistic and pessimistic locking, and how to use thread pools and Future to improve execution efficiency. Finally, it introduces the application scenarios and principles of tools such as CyclicBarrier and CountDownLatch.

Java collections are mainly derived from the Collection and Map interfaces and include subinterfaces such as List, Set, and Queue. List stores ordered duplicate elements, Set stores unique elements, Queue stores elements in a specific order, and Map stores key-value pairs. Collection choices should match requirements such as thread safety and sorting. Java collections provide flexible data storage methods and multiple operations, often more suitable than arrays. The article also compares ArrayList vs. LinkedList for insertion and deletion performance, and HashMap vs. Hashtable for thread safety and efficiency, while noting that ConcurrentHashMap provides better concurrency support.

Reflection is a core mechanism used by frameworks, allowing runtime class analysis and method invocation, and is widely used in frameworks such as Spring. Its advantage is flexibility, but it can also introduce security risks and performance overhead. The proxy pattern extends target object functionality through proxy objects and is divided into static and dynamic proxies, with dynamic proxies being more flexible and commonly used in frameworks. JDK dynamic proxies can only proxy classes that implement interfaces, while CGLIB can proxy classes without interfaces. Dynamic proxies generate bytecode at runtime and provide higher flexibility and efficiency.

Java language features include simplicity, object orientation, platform independence, multithreading support, reliability, and security. Java SE is the base edition suited for desktop applications, while Java EE is the enterprise edition for more complex enterprise applications. The differences among JVM, JDK, and JRE are that JVM runs bytecode, JDK is the development toolkit, and JRE is the runtime environment. Java improves efficiency through bytecode and supports both compilation and interpretation. Exception handling is divided into checked and unchecked exceptions using try-catch-finally. Generics improve readability, reflection provides runtime analysis capabilities, serialization is used for object persistence, and I/O streams are divided into byte streams and character streams. Design patterns such as decorator and adapter are widely used in Java I/O.

This article studies basic web scraping libraries, including Python urllib and requests. It introduces HTTP request construction, exception handling, URL parsing, regular expression usage, and how to extract information from the Maoyan movie ranking page. It also emphasizes advanced usage such as request headers, cookies, proxy settings, and session persistence.

A web crawler is an automated program used to obtain information from web pages. Its basic workflow includes sending HTTP requests to retrieve page source code, extracting the required data, and saving it. Since web pages are built from HTML, CSS, and JavaScript, crawlers need to handle both static and dynamic pages. Sessions and cookies maintain user state, while proxy servers can hide the real IP address. Common request methods include GET and POST, and response status codes indicate request results. Crawlers should follow anti-scraping constraints and use proxies and proper headers to improve efficiency.