Java异常,配置log4j

　　注意:

　　1.Java中的所有异常都是由Throwable类的子类生成的对象，所有的异常类都是Throwable类的子类或子类的子类。Throwable类是Object类的直接子类，Error类和Exception类是Throwable类的两个直接子类。

　　Error  错误类

　　java.lang.Error

　　错误类一般是指虚拟机相关的

　　Exception  异常类

　　2.java.lang.Exception类是Java中所有异常的直接或间接父类

　　java中异常处理是通过5个关键字实现的try,catch,finally,throw,throws

　　throw与throws的区别:

　　throw是语句抛出异常，throws是可能发生异常抛出的声明

　　异常捕获语法:

        try {
            //将可能出错的代码放在此处
        } catch (Exception e) {
            //若try块中发生异常那么将被catch捕获到
        }finally{
            //无论是否出现异常finally都会执行
            //若try或catch中出现System.exit(0)finally块将不执行,因为java虚拟机已被关闭
        }　　　　

　　多路异常捕获语法:

        //多路异常捕获
        try {
            //将可能出错的代码放在此处
        } catch (NullPointerException e) {
            //多路异常捕获子类异常在前
        }catch (Exception e) {
            //父类异常在后
        }finally{
            //无论是否出现异常finally都会执行
            //若try或catch中出现System.exit(0)finally块将不执行,因为java虚拟机已被关闭
        }

　　多路异常捕获要注意:子类异常在前,父类异常在后

配置log4j图片教程(无使用教程):

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　　以下是Exception直接已知子类     AclNotFoundException, ActivationException, AlreadyBoundException

ApplicationException, AWTException, BackingStoreException

BadAttributeValueExpException, BadBinaryOpValueExpException, BadLocationException

BadStringOperationException, BrokenBarrierException, CertificateException, ClassNotFoundException

CloneNotSupportedException, DataFormatException, DatatypeConfigurationException, DestroyFailedException

ExecutionException, ExpandVetoException, FontFormatException, GeneralSecurityException, GSSException

IllegalAccessException, IllegalClassFormatException, InstantiationException, InterruptedException, IntrospectionException

InvalidApplicationException, InvalidMidiDataException, InvalidPreferencesFormatException, InvalidTargetObjectTypeException

InvocationTargetException, IOException, JMException, LastOwnerException, LineUnavailableException, MidiUnavailableException

MimeTypeParseException, NamingException, NoninvertibleTransformException, NoSuchFieldException, NoSuchMethodException

NotBoundException, NotOwnerException, ParseException, ParserConfigurationException, PrinterException, PrintException

PrivilegedActionException, PropertyVetoException, RefreshFailedException, RemarshalException, RuntimeException, SAXException

ServerNotActiveException, SQLException, TimeoutException, TooManyListenersException, TransformerException, UnmodifiableClassException

UnsupportedAudioFileException, UnsupportedCallbackException, UnsupportedFlavorException, UnsupportedLookAndFeelException

URISyntaxException, UserException, XAException, XMLParseException, XPathException

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