springboot+mybatis拦截器不生效问题分析

一、环境信息
SpringBoot:2.3.6.RELEASE
Mybatis-plus:3.3.1
二、碰到问题
今天因业务系统功能需要，使用mybatis的拦截器对ORACLE的数据库会话进行用户当前语言环境设置(NLS_LANGUAGE),碰到拦截器代码不生效的问题，特此记录下来，方便将来查阅。
三、代码如下：
1、在Mybatis的@Configuration相关代码添加如下代码（自动注入到拦截器链）：

/**
 * 更改会话状态
 *
 * @return
 */
@Bean
public AlterSessionInterceptor alterSessionInterceptor() {
    return new AlterSessionInterceptor();
}

2、拦截器代码（拦截StatementHandler的prepare方法，取到Connection执行ALTER SESSION的语句）：
/**

• 更改会话解析器

• 
  *
• @since 2021/7/14
  */

@Slf4j
@Intercepts({@Signature(type = StatementHandler.class, method = "prepare", args = {Connection.class, Integer.class})})
public class AlterSessionInterceptor implements Interceptor {

@Override
public Object intercept(Invocation invocation) throws Throwable {
    Object[] args = invocation.getArgs();
    Connection connection = (Connection) args[0];
    if ("Oracle".equalsIgnoreCase(connection.getMetaData().getDatabaseProductName())) {
        Statement statement = null;
        try {
            statement = connection.createStatement();
            String locale = RequestHelper.getCurrentLocale();
            if ("en_GB".equalsIgnoreCase(locale)) {
                statement.execute("ALTER SESSION SET NLS_LANGUAGE='AMERICAN'");
            } else {
                statement.execute("ALTER SESSION SET NLS_LANGUAGE='SIMPLIFIED CHINESE'");
            }
        } finally {
            statement.close();
        }
    }
    return invocation.proceed();
}

}
在运行调试时发现代码无法执行到拦截逻辑，经过参考分页插件代码，发现需要重载以下方法（代码默认是只要实现intercept这个接口，但是实际上需要多加以下插件的处理逻辑才可以，才会启用Plugin的Proxy）：

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

最终拦截器代码如下：
/**

• 更改会话解析器

• 
  *
• @since 2021/7/14
  */

@Slf4j
@Intercepts({@Signature(type = StatementHandler.class, method = "prepare", args = {Connection.class, Integer.class})})
public class AlterSessionInterceptor implements Interceptor {

@Override
public Object intercept(Invocation invocation) throws Throwable {
    Object[] args = invocation.getArgs();
    Connection connection = (Connection) args[0];
    if ("Oracle".equalsIgnoreCase(connection.getMetaData().getDatabaseProductName())) {
        Statement statement = null;
        try {
            statement = connection.createStatement();
            String locale = RequestHelper.getCurrentLocale();
            if ("en_GB".equalsIgnoreCase(locale)) {
                statement.execute("ALTER SESSION SET NLS_LANGUAGE='AMERICAN'");
            } else {
                statement.execute("ALTER SESSION SET NLS_LANGUAGE='SIMPLIFIED CHINESE'");
            }
        } finally {
            statement.close();
        }
    }
    return invocation.proceed();
}

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

@Override
public void setProperties(Properties properties) {
    // to do nothing
}

}