slf4j日志MDC输出格式

// 自动配置模板
...
<Property name="layout">%d %p %X{traceId} [%t] %c{10}:%M:%L %m%n</Property>
...
<PatternLayout pattern="${layout}"/>
...
// 具体项目覆盖配置的格式
<Property name="layout">%d %p [%t] %c{1.}:%M:%L %X{myTraceId} %m%n</Property>

MDC.put("myTraceId", myTraceId);
try {
    ...
} catch (Exception e) {
    ...
} finally {
    MDC.clear();
}

// options, 对应配置中的key列表
private MdcPatternConverter(final String[] options) {
    super(options != null && options.length > 0 ? "MDC{" + options[0] + '}' : "MDC", "mdc");
    if (options != null && options.length > 0) {
        full = false;
        if (options[0].indexOf(',') > 0) {
            // 按照逗号切分key
            keys = options[0].split(",");
            for (int i = 0; i < keys.length; i++) {
                keys[i] = keys[i].trim();
            }
            key = null;
        } else {
            keys = null;
            key = options[0];
        }
    } else {
        full = true;
        key = null;
        keys = null;
    }
}

// 格式化
public void format(final LogEvent event, final StringBuilder toAppendTo) {
    final ReadOnlyStringMap contextData = event.getContextData();
    // if there is no additional options, we output every single
    // Key/Value pair for the MDC in a similar format to Hashtable.toString()
    // 如果没有附加的属性，我们输出每一个单独的MDC配置的key/value对，类似与Hashtable.toString()的格式
    if (full) {
        if (contextData == null || contextData.size() == 0) {
            toAppendTo.append("{}");
            return;
        }
        appendFully(contextData, toAppendTo);
    } else {
        if (keys != null) {
            if (contextData == null || contextData.size() == 0) {
                toAppendTo.append("{}");
                return;
            }
            // 存在附加属性配置
            appendSelectedKeys(keys, contextData, toAppendTo);
        } else if (contextData != null){
            // otherwise they just want a single key output
            final Object value = contextData.getValue(key);
            if (value != null) {
                StringBuilders.appendValue(toAppendTo, value);
            }
        }
    }
}

// 按照配置的MDC keys输出，输出格式为{key=value,key2=value2}
private static void appendSelectedKeys(final String[] keys, final ReadOnlyStringMap contextData, final StringBuilder sb) {
    // Print all the keys in the array that have a value.
    final int start = sb.length();
    sb.append('{');
    for (int i = 0; i < keys.length; i++) {
        final String theKey = keys[i];
        final Object value = contextData.getValue(theKey);
        if (value != null) { // !contextData.containskey(theKey)
            if (sb.length() - start > 1) {
                sb.append(", ");
            }
            sb.append(theKey).append('=');
            StringBuilders.appendValue(sb, value);
        }
    }
    sb.append('}');
}

<Property name="layout">%d %p [%t] %c{1.}:%M:%L %X{myTraceId,} %m%n</Property>

int index = 1;
logger.info("这是第"+index+"条数据");
logger.info("这是第"+String.valueOf(index)+"条数据");

logger.debug(String format, Object param); //支持一个参数
logger.debug(String format, Object param1, Object param2); //支持两个参数
logger.debug(String format, Object… param); //任意数量参数，构造参数数组具有一定的性能损耗

int index1=1;int index2=2;i
logger.info("这是第{}条数据",index1);
logger.info("这是第{}、{}条数据",index1,index2);

logger.info("{1,2} 这是第{}条数据",index2);
logger.info("{1,2} 这是第{{}}条数据",index2);

/**用”\”转义{}占位符*/
logger.info("\\{} 这是第{}条数据 ",index2);
/**用“\”本身转义“{}”中的”\”*/
logger.info("\\\\{} 这是第{}条数据 ",index3); 

if(logger.isDebugEnabled()){
			logger.info("这是第{}条数据 ",index2);
}

logger.error("Failed to format {}", s, e);

log.debug("Found {} records matching filter: '{}'", records, filter);//slf4j
log.debug("Found " + records + " records matching filter: '" + filter + "'");//log4j