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Understanding Java Thread Dump Analysis

Java thread dump is a key tool for troubleshooting performance issues, deadlocks and blocking problems, recording the status and call stack of all threads at a certain moment in the JVM. The acquisition methods include: 1. Use jstack tool to execute jstack; 2. Send SIGQUIT signals through kill-3; 3. Use graphical tools such as JVisualVM or JConsole to export; 4. Acquire through platform interface in containers or cloud environments. Thread states such as RUNNABLE, BLOCKED, WAITING, etc. can help identify problems. A large number of BLOCKED threads may indicate fierce competition in locks. Too much WAITING may mean slow task processing or unreasonable configuration. The steps for analyzing deadlock are: 1. Find BLO

Jul 24, 2025 am 02:58 AM

How to implement a singleton design pattern in Java?

TheSingletonpatterninJavacanbeimplementedusingvariousapproaches,eachwithspecificadvantages.1.Lazyinitializationwiththreadsafetyusesdouble-checkedlockingandthevolatilekeywordtoensureasingleinstanceiscreatedonlywhenneeded,idealforresource-heavyobjects.

Jul 24, 2025 am 02:53 AM

how to read a file in java line by line

To read Java files line by line, it is recommended to use BufferedReader. The steps are: 1. Introduce the BufferedReader and FileReader classes; 2. Open the file with FileReader and wrap it into a BufferedReader; 3. Use the readLine() method to loop through each line until it returns null; 4. Use try-with-resources to automatically close the resource; 5. Capture and handle possible IOExceptions. Common problems include path errors, insufficient permissions, null pointer exceptions and excessive file sizes, which need to be handled in a targeted manner. Other methods include Scanner (suitable for parsing line content) and File

Jul 24, 2025 am 02:45 AM

Reactive Programming in Java with Project Reactor

ProjectReactor is a Java library based on responsive stream specifications used to handle asynchronous data flows. Its core types are Mono and Flux. 1. Use operators such as map, flatMap, and filter for data flow conversion and processing. 2. Control data flow rate through backpressure mechanisms such as onBackpressureBuffer and onBackpressureDrop. 3. Use onErrorResume, onErrorReturn, and retry for error processing. 4. Use subscribeOn and publishOn to implement thread scheduling. 5. It is widely used in microservice asynchronous calls, event-driven architecture, real-time

Jul 24, 2025 am 02:43 AM

java programming

how to convert list to array in java

In Java, there are three main methods to convert List into arrays: 1. Use the toArray() method to pass newType[0] is more concise and type-safe; 2. You need to manually traverse the conversion for basic type arrays, such as List to int[]; 3. Use StreamAPI (Java8) to achieve more flexible conversion through stream().toArray(Type[]::new). Pay attention to the matching problem of array length and type. Different scenarios can choose the appropriate method according to Java version and requirements.

Jul 24, 2025 am 02:42 AM

How to check if an Array contains a specific value in Java?

There are three common ways to determine whether an array contains a specific value in Java. 1. Use Arrays.asList().contains(), which is suitable for object type arrays, with concise code but not for basic type arrays; 2. Iterate through the array and manually check it, which is suitable for basic type arrays, with light performance but large code volume; 3. Use HashSet to improve search efficiency, which is suitable for scenarios with large data volume and multiple searches, and initialization has performance overhead. Selection should be traded based on array type, performance requirements, and code style.

Jul 24, 2025 am 02:35 AM

Java Concurrency in Practice: A Modern Approach

Use java.util.concurrent as the basis, Java21's Executors.newVirtualThreadPerTaskExecutor() is preferred to handle high-throughput I/O tasks; 2. Follow the principles of immutable objects and thread safety design, avoid sharing mutable states, and use record to define immutable data; 3. Use high-level abstracts such as CompletableFuture and StructuredConcurrency to replace low-level primitives such as synchronized/wait/notify; 4. Make good use of JFR, JMC and thread dumps for concurrency diagnosis, and discover thread hunger in time

Jul 24, 2025 am 02:30 AM

How to sleep a thread in Java?

The easiest way to get a thread to pause execution in Java is to use the Thread.sleep() method. This method causes the current thread to enter a blocking state and pauses the execution of the specified time (in milliseconds or nanoseconds), such as Thread.sleep(1000) means sleeping for 1 second; 1. This method must be placed in the try-catch block to handle InterruptedException; 2. It only affects the current thread, not other threads, and is suitable for multi-threaded environments; 3. It is often used to simulate delays, control loop frequency, and avoid frequent access to resources; 4. The sleep time is inaccurate and is affected by operating system scheduling; 5. Alternative solutions include wait()/notify() and TimeUni

Jul 24, 2025 am 02:30 AM

Connecting to Databases with Java (JDBC)

Make sure to add the JDBC driver of the corresponding database and configure project dependencies; 2. Use the DriverManager.getConnection() method to establish a connection through JDBCURL, username and password; 3. Use Statement or PreparedStatement to execute SQL queries and process ResultSet results; 4. Follow best practices such as using try-with-resources to automatically close resources, use PreparedStatement to prevent SQL injection, properly manage credentials and use connection pools, so as to achieve safe and efficient interaction between Java applications and databases.

Jul 24, 2025 am 02:08 AM

jdbc

Migrating a Legacy Java Application to Java 17 LTS

Evaluate the current status: confirm the JDK version, update the build tool plug-in, analyze dependency compatibility and use jdeps to detect internal API usage; 2. Handle destructive changes: remove discarded functions such as Applets, deal with strong encapsulation restrictions and temporarily open the module or refactor it into a public API through --add-opens; 3. Update the build configuration: Maven set maven.compiler.release=17, Gradle specifies the Java17 toolchain and upgrades to JUnit5; 4. Continuous testing: Run unit and integration tests, gradually introduce new features such as text blocks, pattern matching and Record to ensure stability, and ultimately achieve a safe and efficient Java17 migration.

Jul 24, 2025 am 02:01 AM

how to parse a string to a date in java

There are two main ways to parse strings as dates in Java: use SimpleDateFormat (for Java7 and below) and DateTimeFormatter (recommended for Java8). 1. When using SimpleDateFormat, you need to define the format string and create an instance. Use parse() method to convert the string into a Date object, but you should pay attention to its thread unsafe characteristics; 2. When using DateTimeFormatter, combine LocalDate or LocalDateTime to achieve a safer and modern parsing method; 3. Before parsing, you should ensure that the format matches, and it is recommended to pass regular verification or try-catc

Jul 24, 2025 am 01:57 AM

java 日期解析

Java Logging Best Practices with SLF4J and Logback

Use SLF4J instead of Logback to ensure portability; 2. Replace string splicing with parameterized logs to improve performance; 3. Use TRACE/DEBUG/INFO/WARN/ERROR levels reasonably; 4. Structured logs through MDC for machine resolution; 5. Avoid recording sensitive information such as passwords or PII; 6. Configure AsyncAppender to prevent blocking the main thread; 7. Test log output with ListAppender - Following these practices can make the log truly serve development and operation and maintenance, rather than creating noise.

Jul 24, 2025 am 01:55 AM

What is a Semaphore in Java concurrency?

AsemaphoreinJavaisasynchronizationtoolthatcontrolsaccesstosharedorlimitedresourcesthroughacquire()andrelease()operations.Itworksbymaintainingacountofpermits;threadsmustacquireapermitbeforeaccessingtheresource,andreleaseitafterward.1.Binarysemaphoresh

Jul 24, 2025 am 01:54 AM

java concurrency

how to get current date and time in java

There are three main ways to get the current time in Java: 1. Use java.util.Date to be suitable for simple scenarios. Use newDate() to get the current time and match SimpleDateFormat format; 2. It is recommended to use java.time.LocalDateTime introduced by Java8, and obtain the current time through LocalDateTime.now(), which supports flexible formatting and time zone processing; 3. Get time information with time zones recommended to use ZonedDateTime combined with ZoneId, such as ZonedDateTime.now(ZoneId.of("Asia/Shangh

Jul 24, 2025 am 01:53 AM

java date time