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這篇文章主要講解了“如何解決Spring對(duì)靜態(tài)變量無(wú)法注入的問(wèn)題”,文中的講解內(nèi)容簡(jiǎn)單清晰,易于學(xué)習(xí)與理解,下面請(qǐng)大家跟著小編的思路慢慢深入,一起來(lái)研究和學(xué)習(xí)“如何解決Spring對(duì)靜態(tài)變量無(wú)法注入的問(wèn)題”吧!
今天在學(xué)習(xí)的過(guò)程中想寫一個(gè)連接和線程綁定的JDBCUtils工具類,但測(cè)試時(shí)發(fā)現(xiàn)一直報(bào)空指針異常,上網(wǎng)查了之后Spring并不支持對(duì)靜態(tài)成員變量注入,所以光試用@Autowired肯定是不行的。
可是我們編寫工具類時(shí)肯定是要使用靜態(tài)變量和方法的,我總結(jié)一下我用過(guò)可以實(shí)現(xiàn)對(duì)靜態(tài)成員變量注入的方法。
@Component public class JDBCUtils { @Autowired private static ComboPooledDataSource dataSource; private static ThreadLocal<Connection> tl = new ThreadLocal<Connection>(); public static Connection getThreadConnection(){ Connection conn = tl.get(); if (conn == null){ conn = getConnection(); tl.set(conn); } return conn; } public static DataSource getDataSource(){ return dataSource; } public static Connection getConnection(){ Connection connection = null; try { connection = dataSource.getConnection(); } catch (SQLException e) { e.printStackTrace(); } return connection; } public static void removeThreadConnection(){ tl.remove(); } }
在類前加@Component注解,在set方法上加 @Autowired注解,這里注意兩點(diǎn)
1.配置文件里已經(jīng)配置了變量的相關(guān)參數(shù)
2.靜態(tài)變量自動(dòng)生成set方法時(shí)會(huì)有static修飾,要去掉,否則還是無(wú)法注入
@Component public class JDBCUtils { private static ComboPooledDataSource dataSource; @Autowired public void setDataSource(ComboPooledDataSource dataSource) { JDBCUtils.dataSource = dataSource; }
同樣注意將set方法上的static去掉
public class JDBCUtils { private static ComboPooledDataSource dataSource; public void setDataSource(ComboPooledDataSource dataSource) { this.dataSource = dataSource; } private static ThreadLocal<Connection> tl = new ThreadLocal<Connection>(); public static Connection getThreadConnection(){ Connection conn = tl.get(); if (conn == null){ conn = getConnection(); tl.set(conn); } return conn; } public static DataSource getDataSource(){ return dataSource; } public static Connection getConnection(){ Connection connection = null; try { connection = dataSource.getConnection(); } catch (SQLException e) { e.printStackTrace(); } return connection; } public static void removeThreadConnection(){ tl.remove(); } }
<bean id="JDBCUtils" class="com.cc.utils.JDBCUtils"> <property name="dataSource" ref="dataSource"></property> </bean>
用@PostConstruct加在init方法上,在類初始化后執(zhí)行該方法,對(duì)成員變量賦值。在這之前,我們要改造一下工具類,去掉我們想注入變量的static的修飾符,這樣我們就可以用@Autowired實(shí)現(xiàn)對(duì)其注入。
然后加一個(gè)靜態(tài)的類自身的引用對(duì)象,當(dāng)我們想要變量時(shí)通過(guò)這個(gè)引用對(duì)象來(lái)獲取。
@Component public class JDBCUtils { @Autowired private ComboPooledDataSource dataSource; private static JDBCUtils jdbcUtils; @PostConstruct public void init(){ jdbcUtils = this; this.dataSource = dataSource; } private static ThreadLocal<Connection> tl = new ThreadLocal<Connection>(); public static Connection getThreadConnection(){ Connection conn = tl.get(); if (conn == null){ conn = getConnection(); tl.set(conn); } return conn; } public static DataSource getDataSource(){ return jdbcUtils.dataSource; } public static Connection getConnection(){ Connection connection = null; try { connection = jdbcUtils.dataSource.getConnection(); } catch (SQLException e) { e.printStackTrace(); } return connection; } public static void removeThreadConnection(){ tl.remove(); } }
當(dāng)然這種用初始化方法也可以用xml配置,原理一樣。
public class JDBCUtils { private ComboPooledDataSource dataSource; public void setDataSource(ComboPooledDataSource dataSource) { this.dataSource = dataSource; } private static JDBCUtils jdbcUtils; public void init(){ jdbcUtils = this; this.dataSource = dataSource; } private static ThreadLocal<Connection> tl = new ThreadLocal<Connection>(); public static Connection getThreadConnection(){ Connection conn = tl.get(); if (conn == null){ conn = getConnection(); tl.set(conn); } return conn; } public static DataSource getDataSource(){ return jdbcUtils.dataSource; } public static Connection getConnection(){ Connection connection = null; try { connection = jdbcUtils.dataSource.getConnection(); } catch (SQLException e) { e.printStackTrace(); } return connection; } public static void removeThreadConnection(){ tl.remove(); } }
<bean id="JDBCUtils" class="com.cc.utils.JDBCUtils" init-method="init"> <property name="dataSource" ref="dataSource"></property> </bean>
今天在寫redission 的一個(gè)工具類的時(shí)候,隨手寫出下面的代碼
package com.wt.redission.wtredission.utils; import org.redisson.api.*; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.stereotype.Component; import javax.annotation.PostConstruct; @Component public class RedissionUtilserror { @Autowired private static RedissonClient redissonClient; public static RLock getRLock(String objectName) { RLock rLock =redissonClient.getLock(objectName); return rLock; } //根據(jù)名字獲取map public static <K, V> RMap<K, V> getRMap(String objectName) { RMap<K, V> map = redissonClient.getMap(objectName); return map; } //根據(jù)名字和值設(shè)置map public static void setMap(String objectName,Object key,Object value){ RMap<Object, Object> map =redissonClient.getMap(objectName); map.put(key,value); } //根據(jù)名字獲取set public static <V> RSet<V> getSet(String objectName) { RSet<V> set = redissonClient.getSet(objectName); return set; } //根據(jù)名字和值設(shè)置set public static void setSet(String objectName,Object value){ RSet<Object> set = redissonClient.getSet(objectName); set.add(value); } //根據(jù)名字獲取list public static <V> RList<V> getRList(String objectName) { RList<V> rList = redissonClient.getList(objectName); return rList; } //根據(jù)名字和值設(shè)置list public static void setList(String objectName, int index,Object element ){ RList<Object> objectRList = redissonClient.getList(objectName); objectRList.set(index,element); } //根據(jù)名字獲取bucket public static <T> RBucket<T> getRBucket(String objectName) { RBucket<T> bucket = redissonClient.getBucket(objectName); return bucket; } //根據(jù)名字和值 設(shè)置對(duì)應(yīng)的bucket public static <T> T setBucket(String objectName,String value){ RBucket<Object> bucket = redissonClient.getBucket(objectName); bucket.set(value); T t= (T) bucket.get(); //值類型由返回值確定 return t; } }
乍一看好像沒(méi)問(wèn)題 我寫一個(gè)靜態(tài)方法 然后在方法中使用靜態(tài)變量redissonClient ,哇....,一切看得如此正常
當(dāng)我開(kāi)始測(cè)試時(shí),NPE.............,我去這是怎么回事,自己在想這不科學(xué)啊,怎么會(huì)空指針,于是我開(kāi)始找原因
最后發(fā)現(xiàn)是基礎(chǔ)不牢啊............,對(duì)jvm的類加載機(jī)制幾乎就沒(méi)考慮,簡(jiǎn)要說(shuō)要錯(cuò)誤的原因
jvm在進(jìn)行類加載的時(shí)候,首先會(huì)加載類變量,類方法,也就是我這里被static修飾的方法,然后當(dāng)我調(diào)用靜態(tài)方法進(jìn)行使用的時(shí)候,會(huì)使用到redissionClient,注意這個(gè)redissionClient是通過(guò)autowired進(jìn)來(lái)的,關(guān)鍵問(wèn)題就在這里,autowired的底層是通過(guò)構(gòu)造器和set方法注入bean的
redissionClient被static修飾 并且還是一個(gè)接口 在被調(diào)用的時(shí)候肯定沒(méi)有實(shí)例化
下面提供三種方式正確使用
package com.wt.redission.wtredission.utils; import org.redisson.api.*; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.stereotype.Component; import java.util.List; @Component public class RedissionUtils { private static RedissonClient redissonClient; @Autowired public RedissionUtils(RedissonClient redissonClient){ RedissionUtils.redissonClient=redissonClient; } public static RLock getRLock(String objectName) { RLock rLock = redissonClient.getLock(objectName); return rLock; } //根據(jù)名字獲取map public static <K, V> RMap<K, V> getRMap(String objectName) { RMap<K, V> map = redissonClient.getMap(objectName); return map; } //根據(jù)名字和值設(shè)置map public static void setMap(String objectName,Object key,Object value){ RMap<Object, Object> map =redissonClient.getMap(objectName); map.put(key,value); } //根據(jù)名字獲取set public static <V> RSet<V> getSet(String objectName) { RSet<V> set = redissonClient.getSet(objectName); return set; } //根據(jù)名字和值設(shè)置set public static void setSet(String objectName,Object value){ RSet<Object> set = redissonClient.getSet(objectName); set.add(value); } //根據(jù)名字獲取list public static <V> RList<V> getRList(String objectName) { RList<V> rList = redissonClient.getList(objectName); return rList; } //根據(jù)名字和值設(shè)置list public static void setList(String objectName, int index,Object element ){ RList<Object> objectRList = redissonClient.getList(objectName); objectRList.set(index,element); } //根據(jù)名字獲取bucket public static <T> RBucket<T> getRBucket(String objectName) { RBucket<T> bucket = redissonClient.getBucket(objectName); return bucket; } //根據(jù)名字和值 設(shè)置對(duì)應(yīng)的bucket public static <T> T setBucket(String objectName,String value){ RBucket<Object> bucket = redissonClient.getBucket(objectName); bucket.set(value); T t= (T) bucket.get(); //值類型由返回值確定 return t; } }
package com.wt.redission.wtredission.utils; import org.redisson.api.*; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.stereotype.Component; import javax.annotation.PostConstruct; @Component public class RedissionUtils2 { @Autowired RedissonClient redissonClient; public static RedissionUtils2 redissionUtils; @PostConstruct public void init(){ redissionUtils=this; redissionUtils.redissonClient=this.redissonClient; } public static RLock getRLock(String objectName) { RLock rLock = redissionUtils.redissonClient.getLock(objectName); return rLock; } //根據(jù)名字獲取map public static <K, V> RMap<K, V> getRMap(String objectName) { RMap<K, V> map = redissionUtils.redissonClient.getMap(objectName); return map; } //根據(jù)名字和值設(shè)置map public static void setMap(String objectName,Object key,Object value){ RMap<Object, Object> map =redissionUtils.redissonClient.getMap(objectName); map.put(key,value); } //根據(jù)名字獲取set public static <V> RSet<V> getSet(String objectName) { RSet<V> set = redissionUtils.redissonClient.getSet(objectName); return set; } //根據(jù)名字和值設(shè)置set public static void setSet(String objectName,Object value){ RSet<Object> set = redissionUtils.redissonClient.getSet(objectName); set.add(value); } //根據(jù)名字獲取list public static <V> RList<V> getRList(String objectName) { RList<V> rList = redissionUtils.redissonClient.getList(objectName); return rList; } //根據(jù)名字和值設(shè)置list public static void setList(String objectName, int index,Object element ){ RList<Object> objectRList = redissionUtils.redissonClient.getList(objectName); objectRList.set(index,element); } //根據(jù)名字獲取bucket public static <T> RBucket<T> getRBucket(String objectName) { RBucket<T> bucket = redissionUtils.redissonClient.getBucket(objectName); return bucket; } //根據(jù)名字和值 設(shè)置對(duì)應(yīng)的bucket public static <T> T setBucket(String objectName,String value){ RBucket<Object> bucket = redissionUtils.redissonClient.getBucket(objectName); bucket.set(value); T t= (T) bucket.get(); //值類型由返回值確定 return t; } }
package com.wt.redission.wtredission.utils; import io.micrometer.core.instrument.util.StringUtils; import org.springframework.beans.BeansException; import org.springframework.beans.factory.NoSuchBeanDefinitionException; import org.springframework.context.ApplicationContext; import org.springframework.context.ApplicationContextAware; import org.springframework.context.annotation.Scope; import org.springframework.stereotype.Component; import javax.servlet.http.HttpServletRequest; /** * Spring Context工具類. * * @author:Hohn */ @Component @Scope("singleton") public class SpringUtil implements ApplicationContextAware { /** * Spring應(yīng)用上下文環(huán)境. */ private static ApplicationContext applicationContext; /** * 實(shí)現(xiàn)ApplicationContextAware接口的回調(diào)方法,設(shè)置上下文環(huán)境 * * <br>?param: applicationContext * @throws BeansException */ @Override public void setApplicationContext(ApplicationContext applicationContext) throws BeansException { SpringUtil.applicationContext = applicationContext; } /** * 獲取ApplicationContext. * * <br>?return: ApplicationContext */ public static ApplicationContext getApplicationContext() { return applicationContext; } /** * 獲取對(duì)象. * * <br>?param: name * <br>?return: Object 一個(gè)以所給名字注冊(cè)的bean的實(shí)例 * @throws BeansException */ @SuppressWarnings("unchecked") public static <T> T getBean(String name) throws BeansException { return (T) applicationContext.getBean(name); } /** * 獲取類型為requiredType的對(duì)象. * * <br>?param: clz * <br>?return: * @throws BeansException */ public static <T> T getBean(Class<T> clz) throws BeansException { return (T)applicationContext.getBean(clz); } /** * 如果BeanFactory包含一個(gè)與所給名稱匹配的bean定義,則返回true * * <br>?param: name * <br>?return: boolean */ public static boolean containsBean(String name) { return applicationContext.containsBean(name); } /** * 判斷以給定名字注冊(cè)的bean定義是一個(gè)singleton還是一個(gè)prototype。 * 如果與給定名字相應(yīng)的bean定義沒(méi)有被找到,將會(huì)拋出一個(gè)異常(NoSuchBeanDefinitionException) * <br>?param: name * <br>?return: boolean * @throws NoSuchBeanDefinitionException */ public static boolean isSingleton(String name) throws NoSuchBeanDefinitionException { return applicationContext.isSingleton(name); } /** * <br>?param: name * <br>?return: Class 注冊(cè)對(duì)象的類型 * @throws NoSuchBeanDefinitionException */ public static Class<?> getType(String name) throws NoSuchBeanDefinitionException { return applicationContext.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 * * <br>?param: name * <br>?return: * @throws NoSuchBeanDefinitionException */ public static String[] getAliases(String name) throws NoSuchBeanDefinitionException { return applicationContext.getAliases(name); } /** * 請(qǐng)求頭獲取請(qǐng)求token * @param servletRequest * @return */ public static String getJwtToken(HttpServletRequest servletRequest, String tokenId) { String token = servletRequest.getHeader(tokenId); if (StringUtils.isBlank(token)) { token = servletRequest.getParameter(tokenId); } return token; } }
感謝各位的閱讀,以上就是“如何解決Spring對(duì)靜態(tài)變量無(wú)法注入的問(wèn)題”的內(nèi)容了,經(jīng)過(guò)本文的學(xué)習(xí)后,相信大家對(duì)如何解決Spring對(duì)靜態(tài)變量無(wú)法注入的問(wèn)題這一問(wèn)題有了更深刻的體會(huì),具體使用情況還需要大家實(shí)踐驗(yàn)證。這里是億速云,小編將為大家推送更多相關(guān)知識(shí)點(diǎn)的文章,歡迎關(guān)注!
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