使用MyBatis拦截器对公共字段设置值

在表设计时，通常各个表有一些公共字段，比如主键、创建时间、最后修改时间等。这些字段如果都由开发人员去手动设置，一个是产生无用的代码，另外有可能规则不一致，造成错误。因此对于各个表的公用字段，一般会统一处理，MyBatis和Hibernate都有自身的拦截器，实现对应的接口，并配置即可。
    本文以MyBatis为例说明。假设各个表都有3个公共字段：id、gmt_create、gmt_modified。

package com.nowfox.commons.plugin;

import java.lang.reflect.Field;
import java.util.Date;
import java.util.Properties;

import org.apache.ibatis.executor.Executor;
import org.apache.ibatis.mapping.MappedStatement;
import org.apache.ibatis.mapping.SqlCommandType;
import org.apache.ibatis.plugin.Interceptor;
import org.apache.ibatis.plugin.Intercepts;
import org.apache.ibatis.plugin.Invocation;
import org.apache.ibatis.plugin.Plugin;
import org.apache.ibatis.plugin.Signature;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import com.nowfox.commons.util.IdUtils;

/**
 * 通用数据库拦截器

 * 没有设置id时设置id；插入时，如果没有创建时间补充；更新时间必补充
 * 
 * @author nowfox
 *
 */
@Intercepts({ @Signature(type = Executor.class, method = "update", args = { MappedStatement.class, Object.class }) })
public class CommonDbInterceptor implements Interceptor {
    private Logger logger = LoggerFactory.getLogger(getClass());
    private final static String FIELD_ID = "id";
    private final static String FIELD_GMT_CREATE = "gmtCreate";
    private final static String FIELD_GMT_MODIFIED = "gmtModified";

    @SuppressWarnings({ "rawtypes" })
    @Override
    public Object intercept(Invocation invocation) throws Throwable {
        try {
            Object parameter = invocation.getArgs()[1];
            Date now = new Date();
            Class classParameter = (Class) parameter.getClass();
            Field[] fields = classParameter.getDeclaredFields();
            for (Field field : fields) {
                field.setAccessible(true);
                String fieldName = field.getName();
                if (FIELD_ID.equalsIgnoreCase(fieldName)) {
                    Object value = field.get(parameter);
                    if (value == null) {
                        field.set(parameter, IdUtils.getLongId());
                    }
                } else if (FIELD_GMT_CREATE.equalsIgnoreCase(fieldName)) {
                    Object value = field.get(parameter);
                    if (value == null) {
                        // gmtCreate只有插入才添加
                        MappedStatement mappedStatement = (MappedStatement) invocation.getArgs()[0];
                        SqlCommandType sqlCommandType = mappedStatement.getSqlCommandType();
                        if (SqlCommandType.INSERT.equals(sqlCommandType)) {
                            field.set(parameter, now);
                        }
                    }
                } else if (FIELD_GMT_MODIFIED.equalsIgnoreCase(fieldName)) {
                    field.set(parameter, now);
                }
            }
        } catch (Exception e) {
            logger.error("通用设置值时出错", e);
        }
        return invocation.proceed();
    }

    @Override
    public Object plugin(Object target) {
        return Plugin.wrap(target, this);
    }

    @Override
    public void setProperties(Properties properties) {
    }

}

然后在mybatis-config.xml里指定拦截器

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE configuration  
PUBLIC "-//mybatis.org//DTD Config 3.0//EN"  
"http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
    <settings>
        <setting name="logPrefix" value="dao." />
    </settings>
    <plugins>
        <plugin interceptor="com.nowfox.commons.plugin.CommonDbInterceptor">
        </plugin>
    </plugins>
</configuration>