怎样打印日志

以Slf4j+logbak为例：

　　代码如下：

@Slf4j
public class TestThrowable {
    public static void main(String args[]){
        try{
            returnNum(new int[]{1});
        }catch (Exception e){
            log.error("错误信息" + e.toString());
            log.info("----------");
            log.error("错误信息" + e.getMessage());
            log.info("----------");
            log.error("错误信息:{}", e.toString());
            log.info("----------");
            log.error("错误信息:{}", e);
            log.info("----------");
            log.error("错误信息:", e);
            log.info("----------");
          log.error("错误码:{} 错误信息:", "0001", e);
        }
    }
    private static int returnNum (int [] arr) {
        if (arr[0] == 1) {
            return returnA(arr);
        }
        return -1;
    }
    private static int returnA (int [] arr) {
        return arr[10];
    }
}

　　运行结果如下：

16:11:39.307 [main] ERROR com.test.TestThrowable - 错误信息java.lang.ArrayIndexOutOfBoundsException: 10
16:11:39.314 [main] INFO com.test.TestThrowable - ----------
16:11:39.314 [main] ERROR com.test.TestThrowable - 错误信息10
16:11:39.314 [main] INFO com.test.TestThrowable - ----------
16:11:39.314 [main] ERROR com.test.TestThrowable - 错误信息:java.lang.ArrayIndexOutOfBoundsException: 10
16:11:39.317 [main] INFO com.test.TestThrowable - ----------
16:11:39.323 [main] ERROR com.test.TestThrowable - 错误信息:{}
java.lang.ArrayIndexOutOfBoundsException: 10
    at com.test.TestThrowable.returnA(TestThrowable.java:45)
    at com.test.TestThrowable.returnNum(TestThrowable.java:38)
    at com.test.TestThrowable.main(TestThrowable.java:20)
16:11:39.324 [main] INFO com.test.TestThrowable - ----------
16:11:39.324 [main] ERROR com.test.TestThrowable - 错误信息:
java.lang.ArrayIndexOutOfBoundsException: 10
    at com.test.TestThrowable.returnA(TestThrowable.java:45)
    at com.test.TestThrowable.returnNum(TestThrowable.java:38)
    at com.test.TestThrowable.main(TestThrowable.java:20)
16:11:39.324 [main] INFO com.test.TestThrowable - ----------
16:43:54.855 [main] ERROR com.test.TestThrowable - 错误码:0001 错误信息:
java.lang.ArrayIndexOutOfBoundsException: 10
    at com.test.TestThrowable.returnA(TestThrowable.java:46)
    at com.test.TestThrowable.returnNum(TestThrowable.java:39)
    at com.test.TestThrowable.main(TestThrowable.java:20)

　　得到结果：

　　1、e.toString()返回异常类型和错误信息描述（堆栈信息不完整，不会显示错误的具体方法，发生在哪行代码）

　　2、e.getMessage()返回错误信息描述（堆栈信息不完整，不会显示错误的具体方法，发生在哪行代码）

　　3、log.error("xxx"+e.toString()) 打印堆栈信息不完整，不会显示错误的具体方法，发生在哪行代码

　　4、log.error("xxx"+e.getMessage()) 打印堆栈信息不完整，不会显示错误的具体方法，发生在哪行代码

　　5、log.error("xxx", e) 打印完整的堆栈信息，可以查看到错误发生在哪行代码

　　6、log.error("错误码:{} 错误信息:", "0001", e); 这个打印格式是最好的

========================================================================================

　　Throwable的toString()源码

/**
     * Returns a short description of this throwable.
     * The result is the concatenation of:
     * <ul>
     * <li> the {@linkplain Class#getName() name} of the class of this object
     * <li> ": " (a colon and a space)
     * <li> the result of invoking this object's {@link #getLocalizedMessage}
     *      method
     * </ul>
     * If {@code getLocalizedMessage} returns {@code null}, then just
     * the class name is returned.
     *
     * @return a string representation of this throwable.
     */
    public String toString() {
        String s = getClass().getName();
        String message = getLocalizedMessage();
        return (message != null) ? (s + ": " + message) : s;
    }

　　Throwable的getLocalizedMessage()源码

/**
     * Creates a localized description of this throwable.
     * Subclasses may override this method in order to produce a
     * locale-specific message.  For subclasses that do not override this
     * method, the default implementation returns the same result as
     * {@code getMessage()}.
     *
     * @return  The localized description of this throwable.
     * @since   JDK1.1
     */
    public String getLocalizedMessage() {
        return getMessage();
    }

　　Throwable的getMessage()源码

/**
     * Returns the detail message string of this throwable.
     *
     * @return  the detail message string of this {@code Throwable} instance
     *          (which may be {@code null}).
     */
    public String getMessage() {
        return detailMessage;
    }

　　

　　log源码未分析，未完、待续。