How to build a web in eclipse

Java is passed by value, whether it is a primitive type or an object. For basic types, the actual value of the variable is passed, and modification within the method does not affect the external variable; for objects, a copy of the reference address is passed, and the object content can be modified within the method but the external reference point cannot be changed. For example: modifying the basic type parameters does not affect the original value; modifying the object properties will affect the original object, but letting the parameters point to the new object is invalid. If you need to change the reference itself, you can implement it indirectly by arrays or wrapper classes.

There are three ways to copy files in Java. The first is to use FileInputStream and FileOutputStream, which is suitable for Java7 and earlier versions. By reading byte streams and writing to the target file, it is suitable for understanding the underlying principles but limited performance; the second is to use Files.copy(), which is recommended for Java7 and above versions. The code is concise and efficient, and FileChannel is used internally and supports whether to overwrite existing files; the third is to use ApacheCommonsIO tool class, which is suitable for projects that have been introduced to this library. It has simple operation but requires third-party dependencies to be added. The selection method should be determined based on the Java version, whether third-party libraries are allowed and specific performance requirements.

A common way to create threads in Java is to implement the Runnable interface. 1. Create a class to implement Runnable and override the run() method; 2. Create a Thread object and pass the Runnable instance in; 3. Call start() to start the thread. Compared to inheriting Thread, Runnable avoids single inheritance restrictions, separates tasks from threads, and better supports thread pooling. Java8 can use Lambda to simplify the code. Note that run() does not start threads, the same Runnable can be multiplexed by multiple threads, and start() cannot be called repeatedly after the thread is started.

Java's clone() method implements shallow copying by default when copying objects. If you need deep copying, you need to manually process nested objects. 1. To call clone(), you need to implement the Cloneable interface and override the clone() method. 2. Shallow copy only copies the primitive type values, and object fields copy references. 3. Deep copy requires manually cloning nested objects to avoid reference sharing. 4. Common alternatives include replica constructors and static factory methods for their clearer and safer. 5. Pay attention to exception handling and visibility modifiers when using clone().

TomakeJavaapplicationsrunbetterincontainers,youmustadjustJVMsettingstorespectcontainerlimits,optimizestartuptime,andmonitorperformance.First,use-XX: UseContainerSupporttoensuretheJVMrecognizesmemoryandCPUlimits.Second,set-Xmxto70–80%ofcontainermemory

Java provides a variety of advanced synchronization mechanisms to solve complex concurrency problems. 1. ReentrantLock can enable fair locks to ensure thread request sequence, which is suitable for resource allocation and other scenarios; 2. Condition replaces wait/notify to realize multi-condition waiting wake-up, improving control flexibility; 3. ReadWriteLock allows multiple read threads to be parallelized, improving the performance of read more and write less scenarios; 4. StampedLock supports optimistic read locks, reducing lock overhead when read frequently and conflicts are low, and data consistency needs to be processed by itself.

Common annotations for JavaBeanValidation include: 1.@NotNull verification field is not empty; 2.@NotBlank verification string is not blank; 3.@Size limits length or size; 4.@Min/@Max controls the numerical range; 5.@Email checks the mailbox format; verification triggers can be added by adding @Valid before SpringMVC's Controller parameters and matching BindingResult; custom constraints need to create annotations and implement the ConstraintValidator interface; verification packets can be used to verify different scenarios by specifying groups attributes and defining interfaces.

Netty is mature and flexible, especially suitable for high concurrency and low latency scenarios. It encapsulates complex logic such as event registration and buffer management, and provides unified ChannelAPI, built-in ByteBuf buffer pool, clear thread model and out-of-box functions such as SSL support; the key to performance optimization lies in reasonable thread model and memory management, avoiding time-consuming operations into EventLoop threads, and it is recommended to use independent business thread pools to ensure thread safety through channel.eventLoop().execute(...) and enable PooledByteBufAllocator to reduce GC frequency; protocol analysis is recommended to inherit ByteToMessageDecoder