[Java Exceptions]The base class for all exceptions and errors in 1.java is throwable** throwable** error exception* (check-in exception) (Runtime exception) * * Exceptions in 2.java are divided into runtime exceptions and check-in exceptions. * Run-time exceptions represent runtimeexception and all subclasses, which do not need to be captured in the program, and most can be controlled through code to avoid avoidance. * Check for exceptions except for RuntimeException and all of its subclasses, requires that processing be captured in the program. * * 3. Custom exception classes, which must inherit from an existing exception class, typically inherit exception or runtimeexception*, respectively, to declare a check-time exception and a run-time exception. *** [Capture using try Catch]* * 1. Use try{} to capture potentially problematic code, using multiple catch blocks for different exception handling operations. * When an exception occurs in a try block, the corresponding catch block is entered and the remaining code in the try is no longer executed. ** ！！ After catching an exception with a try catch, the program's exception will not block the program's operation. * * 2.catch blocks can have more than one, generally end with exception, which means catch all exceptions; catch blocks must be small to large in order. * * 3. E.getmessage () get the error message; E.printstacktrace () Prints the wrong stack information * * 4.try_catch in order to ensure that the program is not interrupted, you must ensure that all exceptions in the program are captured. * * 5.finally{} Indicates whether the program has a statement that must be executed for an exception to occur. Typically used for operations such as closing a stream, releasing resources, and so on. Even if there are return;* in the block, you must execute the statement in finally. Use system.exit (int i); The program completely ends and does not perform finally. * * 6.try-finally can be combined to exist, instead of having to include a catch to indicate that an exception has not been processed, executing the statement in finally. Other code cannot be executed. ****** [Throws and throw]* * 1. In the method body, if an exception occurs, you can not make a try-catch capture, you can use throws to throw on the method declaration; * After it is thrown, it is captured by the place where the method is called, and if not captured, it can continue to be thrown. * In principle, exception handling must be done in the main method, which will cause the program to fail to discover if it continues to throw. * * 2.throws If you throw more than one exception to use, separate. * * 3.throw throws an exception manually in the program public static void Setage (int i) {if (i<0| | I>100) {* Throw new IllegalArgumentException ("The age you entered is not legal"); * * 4. If you throw a check-type exception using throw, you must use throws on the method body to throw an exception, If you throw a run-time exception with throw, you do not need to throw an exception on the method body. * * 5 If the exception system does not throw new RuntimeException ("Exception"), or throw new* Exception ("Exception"). } }"Common exceptions"ArithmeticException-Arithmetic Operation exception numberformatexception-numeric format exception indexoutofboundsexception- Subscript out-of-bounds exception negativearraysizeexception-Creates an array with a negative size error exception NullPointerException-NULL pointer reference exception classcastexception-type cast exception.* [use of log4j]* * 1. Import Log4j.jar add** 2. Create log4j.propeities** 3 in the log4j sibling directory. In the class that needs to print the log, get a Log object by Logger.getlogger (the class name. Class). * * 4. Use the Log object to invoke different levels of print statements, respectively, for the output of the log. * Logr.debug ("Print a debug Message"), Logr.info ("Print a Info"), Logr.warn ("Print a warn message"), Logr.error ("Print an error message"); #1. Log4j.rootlogger = Total Configuration # log4j.rootlogger=[level],appendername1 (adapter name), Appendername2. [level]:error 3Warn 4INFO 6DEBUG 7#log4j.rootlogger= Setting info indicates that the level is greater than info can be log output. Log4j.rootlogger=debug, logfile,stdout #2. Configure each adapter, # Log4j.appender. Adapter name = Specify the output destination for the log # Org.apache.log4j.ConsoleAppender (console), # Org.apache.log4j.FileAppender (file), # Org.apache.log4j.DailyRollingFileAppender (Generate a log file every day), # Org.apache.log4j.RollingFileAppender (creates a new file when the file size reaches the specified size), # Org.apache.log4j.WriterAppender (sends the log information in stream format to any specified place) #3. log4j.appender.stdout.target= set the console to print the statement style (only if the console has one) # 4.log4j.appender.logfile.append = True true, does not overwrite, False writes when the file is emptied and then written. #5. log4j.appender.logfile.Threshold = Debug Sets a separate level for the current adapter. #6. log4j.appender.logfile.layout= which layout structure to use for log display# org.apache.log4j.HTMLLayout (layout in HTML table), # org.apache.log4j.PatternLayout (flexibility to specify layout mode), # Org.apache.log4j.SimpleLayout (contains the level and information string for log information), # Org.apache.log4j.TTCCLayout (contains information about the time, thread, category, etc.) #7 of log generation. log4j.appender.logfile.layout.conversionpattern= sets the format of the patternlayout. #%M The message specified in the output code #%p output priority, that is, debug,info,warn,error,fatal#%r output from the application boot to output the log information in the number of milliseconds #%c output belongs to the class, usually the full name of the class #%t Output the thread name that generated the log event #%n output a carriage return newline, the Windows platform is "\ r \ n", the UNIX platform is "\ n" #%d output the date or time of the log point, the default format is ISO8601, you can specify the format later, such as:%d{yyy MMM DD HH:mm:ss, SSS}, output similar to: October 18, 2002 22:10:28, 921#%l The occurrence of the output log event, including the name of the class, the thread that occurred, and the number of rows in the code. Example: Testlog4.main (testlog4.java:10) #8. LOG4J.APPENDER.LOGFILE.MAXFILESIZE=20MB You can set the maximum file size when Org.apache.log4j.RollingFileAppender. #90log4j. appender.logfile.maxbackupindex=10 Org.apache.log4j.RollingFileAppender You can set the maximum number of files.
Getting Started with Java article nineth: Exceptions and log4j use
