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How to filter a List using Java 8 Stream API?

In Java 8, using the filter() method of StreamAPI combined with Lambda expressions can efficiently filter Lists. 1. Basic filtering: If you keep integers greater than 10, you need to use filter(n->n>10); 2. The filtering object list can be judged by object properties, such as filter(p->p.getAge()>30); 3. Multi-condition filtering can be implemented using logical operations combinations or chain calls; 4. The results can be further processed in combination with map() or limit(), such as extracting attributes or limiting the number.

Jul 23, 2025 am 02:52 AM

Securing Java Applications against OWASP Top 10

Preventinjectionbyusingparameterizedqueries,querybuilders,andinputvalidation;2.SecureauthenticationwithSpringSecurityorApacheShiro,enforcestrongpasswords,MFA,andsecuresessioncookies;3.Protectsensitivedataviabcrypt/PBKDF2forpasswords,AES-256-GCMencryp

Jul 23, 2025 am 02:18 AM

java security

Creating and Using Custom Exceptions in Java

Custom exceptions can improve code readability and maintenance and are suitable for specific error scenarios in business logic. In Java development, standard exception classes such as NullPointerException and IOException can only express common errors and cannot accurately describe complex business problems, such as "insufficient user balance" or "illegal order status". At this time, using custom exceptions (such as InsufficientBalanceException) can allow the caller to understand the nature of the error more clearly. To create a custom exception, you only need to inherit Exception or RuntimeException and provide a constructor with String parameters; if you need an unchecked exception,

Jul 23, 2025 am 02:05 AM

The Role of Java in Big Data and Apache Spark

JavamattersinBigDataduetoJVMecosystem,maturelibraries,andenterpriseadoption;2.JavapairspowerfullywithApacheSparkviafullAPIsupport,performanceparity,andseamlesstoolintegration;3.UseJavawithSparkwhenteamsknowJava,buildingenterpriseapps,needingconcurren

Jul 23, 2025 am 02:02 AM

How the Java `equals()` and `hashCode()` Methods Work

The equals() and hashCode() methods must be rewrite correctly at the same time, otherwise the hash set (such as HashMap and HashSet) will be invalid; 2. Equals() is used to define the logical equality of objects, and the actual field values need to be compared instead of references; 3. HashCode() returns the object hash code, and it is necessary to ensure that the equal objects have the same hash value; 4. Violating the contract will make it impossible to find the stored object from the collection, because hash search first uses hashCode() to locate the bucket, and then uses equals() to confirm the match; 5. It is recommended to use Objects.equals() and Objects.hash() to implement null safe and consistent logic, and avoid objects used as keys.

Jul 23, 2025 am 02:02 AM

java equals()

Java Futures and Promises for Asynchronous Operations

Future is suitable for simple asynchronous tasks, while CompletableFuture provides more flexible chain calls and combination operations. 1. Future submits tasks through ExecutorService, using get() to get results, but the functions are limited; 2. CompletableFuture supports thenApply, thenAccept, exceptionally and other methods, which can realize chain processing and exception capture; 3. Complete() can be called manually to complete Future; 4. It is recommended to customize thread pools to optimize resource management to avoid blocking public thread pools; 5. Configure the number of threads reasonably according to the task type, and web applications can combine with frameworks

Jul 23, 2025 am 01:50 AM

Understanding Java Memory Model (JMM) Internals

Java Memory Model (JMM) is a set of specifications that solve the problems of visibility, orderliness and atomicity in concurrent programming. 1. The volatile keyword ensures the visibility of variables and prohibits instruction reordering, but does not guarantee the atomicity of composite operations; 2. Synchronized not only realizes mutually exclusive access, but also establishes happens-before relationships to ensure data consistency; 3. After the final field is assigned in the constructor, other threads can correctly see their initialization values, which is an important means to build thread-safe objects. Mastering the memory semantics of these keywords helps to write stable and reliable concurrent code.

Jul 23, 2025 am 01:08 AM

Advanced Java Logging Configuration with MDC

MDC is a thread binding context map provided by SLF4J, which is used to add custom information to the log to improve traceability. 1. Use MDC.put(key,value) to add context data, such as user ID and request ID; 2. Output these fields through %X{key} in the log configuration (such as Logback, Log4j2); 3. Automatically inject MDC information through interceptors or filters in web applications, and call MDC.clear() after the request is completed; 4. Manually pass the MDC context in multi-threaded or asynchronous tasks, which can be implemented by encapsulating the Executor or using a third-party library; 5. Configure the log framework (such as Logback, Log4j2) to ensure correct input

Jul 23, 2025 am 12:51 AM

How to use regular expressions in Java to validate an email?

The method to verify the mailbox format in Java is to use regular expressions to match the Pattern and Matcher classes. 1. Use Pattern and Matcher classes: generate Pattern objects by compiling regular expressions, and then create Matcher objects to match input strings; 2. Mailbox regular structure: including user name part, domain name part and top-level domain name part, which can cover most legal mailbox formats; 3. Notes: There is no need to pursue full compliance with RFC standards, front-end and back-end double-factor verification should be taken into account, and third-party libraries such as Apache CommonsValidator can be considered; 4. Sample test code: Write test methods to verify legal and illegal mailboxes to ensure accuracy.

Jul 23, 2025 am 12:50 AM

What is type erasure in Java generics?

Java's generic type erasure is the mechanism by which the compiler erases specific type information when processing generics. 1. Java will remove generic information during compilation, so that List and List are regarded as the same type at runtime; 2. This design is to be compatible with versions before Java 1.5; 3. Generic types will be replaced with boundary types, such as T is replaced with Object, TextendsNumber is replaced with Number, and the compiler inserts type conversion to ensure security; 4. Type erasure causes problems such as inability to create generic arrays, inability to check generic types with instanceof, and signature conflicts of different generic methods; 5. You can obtain parent class generic information through reflection or use anonymous internal classes to save generics to bypass

Jul 23, 2025 am 12:15 AM

java generics Type erasure

Java Native Memory Diagnostics and Tools

Confirm that the NativeMemory problem is manifested as normal heap memory but the total process memory is growing, the RES memory is far beyond the -Xmx setting, and an OOM error of Directbuffer or nativethread. 1. Use NMT (-XX:NativeMemoryTracking=summary) to track the native memory of JVM and view the memory trends of modules such as Thread and Internal through jcmd; 2. Pay attention to the DirectBuffer leakage, it is not released when using allocateDirect() or the MaxDirectMemorySize setting is unreasonable; 3. Check that too many threads lead to high stack space occupancy, which can be used

Jul 23, 2025 am 12:09 AM

java programming

Developing Serverless Java Functions on AWS Lambda

JavaissuitableforAWSLambdainspecificscenariosdespitenotbeingthemostcommonchoice.TodevelopJava-basedLambdafunctionseffectively,firstsetupyourenvironmentusingMavenorGradle,installAWSSAMCLIorServerlessFramework,useJava8or11,configureanIDEwithAWSToolkitp

Jul 22, 2025 am 04:37 AM

how to override toString method in java

The main purpose of overriding the toString() method is to return a more meaningful representation of the object string. The default toString() outputs class name and hash code, such as com.example.Person@1b6d3586, which is not conducive to debugging and log analysis, and after rewriting, you can output such as Person{name='Alice',age=30}, which is convenient for quick understanding of object status. When rewriting, you need to use @Override annotation to return clear format and avoid null or complex logic. Suitable for debugging, logging, unit testing, and collection output. Mainstream IDEs such as IntelliJ and Eclipse provide the function of automatically generating toString(), L

Jul 22, 2025 am 04:37 AM

Understanding Java Class Loader Leakage

The main reasons for the Java class loader leak are that the thread context class loader is not reset, the static variable holds the class loader or class instance, the listener and callback are not logged out, and the JDBC driver registration is not cleared. 1. The thread context class loader has not been restored after use, so it should be set and restored manually; 2. Static variables hold the class loader or the classes it loads for a long time, so it cannot be recycled. It is recommended to replace strong references with weak references; 3. The listener and callback are not logged out, which will cause the class loader to be unable to be released, and it should be explicitly unregistered when closed; 4. The JDBC driver is not removed from DriverManager, which will also cause leakage, and should be actively cleaned before the application is closed. Such problems can be effectively prevented through code specifications, resource management and memory analysis tools.

Jul 22, 2025 am 03:57 AM

java