1.使用場景

springboot使用mybatis開啟redis二級快取，使用的程式碼如下：

ApplicationContextHolder.java

import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;
import org.springframework.context.annotation.Lazy;
import org.springframework.stereotype.Component;

@Component
public class ApplicationContextHolder implements ApplicationContextAware {

    private static ApplicationContext applicationContext;

    /**
     * 實現ApplicationContextAware介面的context注入函式, 將其存入靜態變數.
     */
    @Override
    public void setApplicationContext(ApplicationContext applicationContext) {
        ApplicationContextHolder.applicationContext = applicationContext; // NOSONAR
    }

    /**
     * 取得儲存在靜態變數中的ApplicationContext.
     */
    public static ApplicationContext getApplicationContext() {
        checkApplicationContext();
        return applicationContext;
    }

    /**
     * 從靜態變數ApplicationContext中取得Bean, 自動轉型為所賦值物件的型別.
     */
    @SuppressWarnings("unchecked")
    public static <T> T getBean(String name) {
        checkApplicationContext();
        return (T) applicationContext.getBean(name);
    }

    /**
     * 從靜態變數ApplicationContext中取得Bean, 自動轉型為所賦值物件的型別.
     */
    @SuppressWarnings("unchecked")
    public static <T> T getBean(Class<T> clazz) {
        checkApplicationContext();
        return (T) applicationContext.getBeansOfType(clazz);
    }

    /**
     * 清除applicationContext靜態變數.
     */
    public static void cleanApplicationContext() {
        applicationContext = null;
    }

    private static void checkApplicationContext() {
        if (applicationContext == null) {
            throw new IllegalStateException("applicaitonContext未注入,請在applicationContext.xml中定義SpringContextHolder");
        }
    }
}

RedisCacheServiceImpl.java

import dgis.lite.usgs.ApplicationContextHolder;
import dgis.lite.usgs.utils.SpringUtils;
import org.apache.ibatis.cache.Cache;
import org.springframework.boot.autoconfigure.AutoConfigureAfter;
import org.springframework.context.annotation.Configuration;
import org.springframework.dao.DataAccessException;
import org.springframework.data.redis.connection.RedisConnection;
import org.springframework.data.redis.core.RedisCallback;
import org.springframework.data.redis.core.RedisTemplate;
import org.springframework.stereotype.Component;
import org.springframework.util.CollectionUtils;

import java.util.Set;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.ReadWriteLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;


public class RedisCacheServiceImpl implements Cache {

    // 讀寫鎖
    private final ReadWriteLock readWriteLock = new ReentrantReadWriteLock(true);

        private RedisTemplate<String, Object> redisTemplate = ApplicationContextHolder.getBean("redisTemplate");
 


    private String id;

    public RedisCacheServiceImpl(final String id) {
        if (id == null) {
            throw new IllegalArgumentException("Cache instances require an ID");
        }
        this.id = id;
    }

    @Override
    public String getId() {
        return this.id;
    }

    @Override
    public void putObject(Object key, Object value) {
        if (value != null) {
            // 向Redis中新增資料，有效時間是1小時
            redisTemplate.opsForValue().set(key.toString(), value, 1, TimeUnit.HOURS);
        }
    }

    @Override
    public Object getObject(Object key) {
        try {
            if (key != null) {
                Object obj = redisTemplate.opsForValue().get(key.toString());
                return obj;
            }
        } catch (Exception e) {
        }
        return null;
    }

    @Override
    public Object removeObject(Object key) {
        try {
            if (key != null) {
                redisTemplate.delete(key.toString());
            }
        } catch (Exception e) {
        }
        return null;
    }

    @Override
    public void clear() {
        try {
            Set<String> keys = redisTemplate.keys("*:" + this.id + "*");
            if (!CollectionUtils.isEmpty(keys)) {
                redisTemplate.delete(keys);
            }
        } catch (Exception e) {
        }
    }

    @Override
    public int getSize() {
        Long size = (Long) redisTemplate.execute(new RedisCallback<Long>() {
            @Override
            public Long doInRedis(RedisConnection connection) throws DataAccessException {
                return connection.dbSize();
            }
        });
        return size.intValue();
    }

    @Override
    public ReadWriteLock getReadWriteLock() {
        return this.readWriteLock;
    }
}

2.出現問題

applicaitonContext屬性未注入, 請在applicationContext.xml中定義SpringContextHolder.

這個異常其實是在 ApplicationContextHolder.java 中我們自己寫的異常，出現原因是因為 mapper中定義的快取型別載入的比ApplicationContextHolder快，也就是說ApplicationContextHolder還沒有初始化好，mapper就開始初始化了。

3.解決方法

網上搜了一大堆方法，都是複製貼上的，最後處理方法其實比較簡單，就是不使用ApplicationContextHolder這個類，直接使用SpringUtils.getBean類初始化redisTemplate。即：

 private RedisTemplate<String, Object> redisTemplate = SpringUtils.getBean("redisTemplate");

修改後的RedisCacheServiceImpl.java

import dgis.lite.usgs.ApplicationContextHolder;
import dgis.lite.usgs.utils.SpringUtils;
import org.apache.ibatis.cache.Cache;
import org.springframework.boot.autoconfigure.AutoConfigureAfter;
import org.springframework.context.annotation.Configuration;
import org.springframework.dao.DataAccessException;
import org.springframework.data.redis.connection.RedisConnection;
import org.springframework.data.redis.core.RedisCallback;
import org.springframework.data.redis.core.RedisTemplate;
import org.springframework.stereotype.Component;
import org.springframework.util.CollectionUtils;

import java.util.Set;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.ReadWriteLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;


public class RedisCacheServiceImpl implements Cache {

    // 讀寫鎖
    private final ReadWriteLock readWriteLock = new ReentrantReadWriteLock(true);

    private RedisTemplate<String, Object> redisTemplate = SpringUtils.getBean("redisTemplate");

    private String id;

    public RedisCacheServiceImpl(final String id) {
        if (id == null) {
            throw new IllegalArgumentException("Cache instances require an ID");
        }
        this.id = id;
    }

    @Override
    public String getId() {
        return this.id;
    }

    @Override
    public void putObject(Object key, Object value) {
        if (value != null) {
            // 向Redis中新增資料，有效時間是1小時
            redisTemplate.opsForValue().set(key.toString(), value, 1, TimeUnit.HOURS);
        }
    }

    @Override
    public Object getObject(Object key) {
        try {
            if (key != null) {
                Object obj = redisTemplate.opsForValue().get(key.toString());
                return obj;
            }
        } catch (Exception e) {
        }
        return null;
    }

    @Override
    public Object removeObject(Object key) {
        try {
            if (key != null) {
                redisTemplate.delete(key.toString());
            }
        } catch (Exception e) {
        }
        return null;
    }

    @Override
    public void clear() {
        try {
            Set<String> keys = redisTemplate.keys("*:" + this.id + "*");
            if (!CollectionUtils.isEmpty(keys)) {
                redisTemplate.delete(keys);
            }
        } catch (Exception e) {
        }
    }

    @Override
    public int getSize() {
        Long size = (Long) redisTemplate.execute(new RedisCallback<Long>() {
            @Override
            public Long doInRedis(RedisConnection connection) throws DataAccessException {
                return connection.dbSize();
            }
        });
        return size.intValue();
    }

    @Override
    public ReadWriteLock getReadWriteLock() {
        return this.readWriteLock;
    }
}

　　SpringUtils.java

import org.apache.commons.lang.StringUtils;
import org.springframework.aop.framework.AopContext;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.NoSuchBeanDefinitionException;
import org.springframework.beans.factory.config.BeanFactoryPostProcessor;
import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;
import org.springframework.stereotype.Component;

@Component
public class SpringUtils implements BeanFactoryPostProcessor, ApplicationContextAware {

    /**
     * Spring 應用上下文環境
     */
    private static ConfigurableListableBeanFactory beanFactory;

    private static ApplicationContext applicationContext;

    public SpringUtils() {
    }

    @Override
    public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
        SpringUtils.beanFactory = beanFactory;
    }

    @Override
    public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
        SpringUtils.applicationContext = applicationContext;
    }

    /**
     * 獲取物件
     *
     * @param name
     * @return Object 一個以所給名字註冊的 bean 的例項
     * @throws BeansException
     */
    @SuppressWarnings("unchecked")
    public static <T> T getBean(String name) throws BeansException {
        return (T) beanFactory.getBean(name);
    }

    /**
     * 獲取型別為 requiredType 的物件
     *
     * @param clz
     * @return
     * @throws BeansException
     */
    public static <T> T getBean(Class<T> clz) throws BeansException {
        T result = (T) beanFactory.getBean(clz);
        return result;
    }

    /**
     * 如果 BeanFactory 包含一個與所給名稱匹配的 bean 定義，則返回 true
     *
     * @param name
     * @return boolean
     */
    public static boolean containsBean(String name) {
        return beanFactory.containsBean(name);
    }

    /**
     * 判斷以給定名字註冊的 bean 定義是一個 singleton 還是一個 prototype。 如果與給定名字相應的 bean 定義沒有被找到，將會丟擲一個異常（NoSuchBeanDefinitionException）
     *
     * @param name
     * @return boolean
     * @throws NoSuchBeanDefinitionException
     */
    public static boolean isSingleton(String name) throws NoSuchBeanDefinitionException {
        return beanFactory.isSingleton(name);
    }

    /**
     * @param name
     * @return Class 註冊物件的型別
     * @throws NoSuchBeanDefinitionException
     */
    public static Class<?> getType(String name) throws NoSuchBeanDefinitionException {
        return beanFactory.getType(name);
    }

    /**
     * 如果給定的 bean 名字在 bean 定義中有別名，則返回這些別名
     *
     * @param name
     * @return
     * @throws NoSuchBeanDefinitionException
     */
    public static String[] getAliases(String name) throws NoSuchBeanDefinitionException {
        return beanFactory.getAliases(name);
    }

    /**
     * 獲取 aop 代理物件
     *
     * @param invoker
     * @return
     */
    @SuppressWarnings("unchecked")
    public static <T> T getAopProxy(T invoker) {
        return (T) AopContext.currentProxy();
    }

    /**
     * 獲取當前的環境配置，無配置返回 null
     *
     * @return 當前的環境配置
     */
    public static String[] getActiveProfiles() {
        return applicationContext.getEnvironment().getActiveProfiles();
    }

    /**
     * 獲取當前的環境配置，當有多個環境配置時，只獲取第一個
     *
     * @return 當前的環境配置
     */
    public static String getActiveProfile() {
        final String[] activeProfiles = getActiveProfiles();
        return StringUtils.isNotEmpty(String.valueOf(activeProfiles)) ? activeProfiles[0] : null;
    }

}

　　現在打包jar，執行正常。