To correctly handle JDBC transactions, you must first turn off the automatic commit mode, then perform multiple operations, and finally commit or rollback according to the results; 1. Call conn.setAutoCommit(false) to start the transaction; 2. Execute multiple SQL operations, such as INSERT and UPDATE; 3. Call conn.commit() if all operations are successful, and call conn.rollback() if an exception occurs to ensure data consistency; at the same time, try-with-resources should be used to manage resources, properly handle exceptions and close connections to avoid connection leakage; in addition, it is recommended to use connection pools and set save points to achieve partial rollback, and keep transactions as short as possible to improve performance.

Use classes in the java.time package to replace the old Date and Calendar classes; 2. Get the current date and time through LocalDate, LocalDateTime and LocalTime; 3. Create a specific date and time using the of() method; 4. Use the plus/minus method to immutably increase and decrease the time; 5. Use ZonedDateTime and ZoneId to process the time zone; 6. Format and parse date strings through DateTimeFormatter; 7. Use Instant to be compatible with the old date types when necessary; date processing in modern Java should give priority to using java.timeAPI, which provides clear, immutable and linear

To calculate the difference between two dates, you need to select the corresponding function according to the database type: 1. Use DATEDIFF() to calculate the day difference in MySQL, or specify the units such as HOUR and MINUTE in TIMESTAMPDIFF(); 2. Use DATEDIFF(date_part, start_date, end_date) in SQLServer and specify the units; 3. Use direct subtraction in PostgreSQL to obtain the day difference, or use EXTRACT(DAYFROMAGE(...)) to obtain more accurate intervals; 4. Use julianday() function to subtract the day difference in SQLite; always pay attention to the date order

Install the corresponding database driver; 2. Use connect() to connect to the database; 3. Create a cursor object; 4. Use execute() or executemany() to execute SQL and use parameterized query to prevent injection; 5. Use fetchall(), etc. to obtain results; 6. Commit() is required after modification; 7. Finally, close the connection or use a context manager to automatically handle it; the complete process ensures that SQL operations are safe and efficient.

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Java's garbage collection (GC) is a mechanism that automatically manages memory, which reduces the risk of memory leakage by reclaiming unreachable objects. 1.GC judges the accessibility of the object from the root object (such as stack variables, active threads, static fields, etc.), and unreachable objects are marked as garbage. 2. Based on the mark-clearing algorithm, mark all reachable objects and clear unmarked objects. 3. Adopt a generational collection strategy: the new generation (Eden, S0, S1) frequently executes MinorGC; the elderly performs less but takes longer to perform MajorGC; Metaspace stores class metadata. 4. JVM provides a variety of GC devices: SerialGC is suitable for small applications; ParallelGC improves throughput; CMS reduces

JavaFlightRecorder(JFR)isessentialfordiagnosingproductionJavaissueswithminimaloverhead.1.JFRcapturescriticalruntimedataincludingCPUprofiling,garbagecollection,threadactivity,exceptions,I/O,andJVMinternals,enablinganalysisoflatencyspikes,memoryleaks,d

defer is used to perform specified operations before the function returns, such as cleaning resources; parameters are evaluated immediately when defer, and the functions are executed in the order of last-in-first-out (LIFO); 1. Multiple defers are executed in reverse order of declarations; 2. Commonly used for secure cleaning such as file closing; 3. The named return value can be modified; 4. It will be executed even if panic occurs, suitable for recovery; 5. Avoid abuse of defer in loops to prevent resource leakage; correct use can improve code security and readability.