目前，比较流行的Log Framework 有：Apache Commons Logging，Avalon LogKit，log4j，SLF4J 等，ObjectiveSQL 无法确定应用系统使用哪一种 Log Framework，所以提供了扩展接口，由应用系统根据自身的需要进行实现，以Slf4j 为示例，详细介绍应用系统如何扩展实现Log Framework。

ObjectiveSQL 中的扩展接口Logger.java 和LoggerFactory.java 如下：

public interface Logger {

    void debug(long elapsedTime, String sql, Object[] params);

    void info(long elapsedTime, String sql, Object[] params);

    void error(String message, Throwable throwable);
}

public interface LoggerFactory {

    Logger create(Class<?> clazz);
}

结合SpringBoot 示例如下：

import com.github.braisdom.objsql.Logger;
import com.github.braisdom.objsql.LoggerFactory;
import com.github.braisdom.objsql.util.StringUtil;

import java.util.Arrays;

public class ObjLoggerFactoryImpl implements LoggerFactory {

    private class ObjLoggerImpl implements Logger {

        private final org.slf4j.Logger logger;

        public ObjLoggerImpl(org.slf4j.Logger logger) {
            this.logger = logger;
        }

        @Override
        public void debug(long elapsedTime, String sql, Object[] params) {
            logger.debug(createLogContent(elapsedTime, sql, params));
        }

        @Override
        public void info(long elapsedTime, String sql, Object[] params) {
            logger.info(createLogContent(elapsedTime, sql, params));
        }

        @Override
        public void error(String message, Throwable throwable) {
            logger.error(message, throwable);
        }

        private String createLogContent(long elapsedTime, String sql, Object[] params) {
            String[] paramStrings = Arrays.stream(params).map(param -> String.valueOf(param)).toArray(String[]::new);
            String paramString = String.join(",", paramStrings);
            return String.format("[%dms] %s, with: [%s]", elapsedTime, sql, String.join(",",
                    paramString.length() > 100 ? StringUtil.truncate(paramString, 99) : paramString));
        }
    }

    @Override
    public Logger create(Class<?> clazz) {
        org.slf4j.Logger logger = org.slf4j.LoggerFactory.getLogger(clazz);
        return new ObjLoggerImpl(logger);
    }
}

LoggerFactory loggerFactory = new ObjLoggerFactoryImpl();
Databases.installLoggerFactory(loggerFactory);

其实，原理很简单，只需要按要求实现Logger 和LoggerFactory 两个接口，在接口中注入自身Log Framework 的实现即可，示例中是以Slf4j 为示例，其它类型的Framework 也类似。完成具体实现后，需要将实例注入ObjectiveSQL。