文章详情

短信预约-IT技能 免费直播动态提醒

请输入下面的图形验证码

提交验证

短信预约提醒成功

Spring对静态变量无法注入的解决方案

2024-04-02 19:55

关注

Spring对静态变量无法注入

问题

今天在学习的过程中想写一个连接和线程绑定的JDBCUtils工具类,但测试时发现一直报空指针异常,上网查了之后Spring并不支持对静态成员变量注入,所以光试用@Autowired肯定是不行的。

可是我们编写工具类时肯定是要使用静态变量和方法的,我总结一下我用过可以实现对静态成员变量注入的方法。


@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();
    }
}

set方法注入

注解方式

在类前加@Component注解,在set方法上加 @Autowired注解,这里注意两点

1.配置文件里已经配置了变量的相关参数

2.静态变量自动生成set方法时会有static修饰,要去掉,否则还是无法注入


@Component
public class JDBCUtils {
    private static ComboPooledDataSource dataSource;
    @Autowired
    public void setDataSource(ComboPooledDataSource dataSource) {
        JDBCUtils.dataSource = dataSource;
    }

xml方式

同样注意将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>

@PostConstruct注解方式注入

用@PostConstruct加在init方法上,在类初始化后执行该方法,对成员变量赋值。在这之前,我们要改造一下工具类,去掉我们想注入变量的static的修饰符,这样我们就可以用@Autowired实现对其注入。

然后加一个静态的类自身的引用对象,当我们想要变量时通过这个引用对象来获取。


@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();
    }
}

当然这种用初始化方法也可以用xml配置,原理一样。


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>

静态方法注入bean失败原因

今天在写redission 的一个工具类的时候,随手写出下面的代码


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;
    } 
 
    //根据名字获取map
    public static  <K, V> RMap<K, V> getRMap(String objectName) {
        RMap<K, V> map = redissonClient.getMap(objectName);
        return map;
    }
 
    //根据名字和值设置map
    public static void setMap(String objectName,Object key,Object value){
        RMap<Object, Object> map =redissonClient.getMap(objectName);
        map.put(key,value);
    } 
 
    //根据名字获取set
    public static <V> RSet<V> getSet(String objectName) {
        RSet<V> set = redissonClient.getSet(objectName);
        return set;
    }
 
    //根据名字和值设置set
    public static void setSet(String objectName,Object value){
        RSet<Object> set = redissonClient.getSet(objectName);
        set.add(value);
    }
 
    //根据名字获取list
    public static  <V> RList<V> getRList(String objectName) {
        RList<V> rList = redissonClient.getList(objectName);
        return rList;
    } 
 
    //根据名字和值设置list
    public static void setList(String objectName, int  index,Object element ){
        RList<Object> objectRList = redissonClient.getList(objectName);
        objectRList.set(index,element);
    }
 
    //根据名字获取bucket
    public static <T> RBucket<T> getRBucket(String objectName) {
        RBucket<T> bucket = redissonClient.getBucket(objectName);
        return bucket;
    }
 
    //根据名字和值 设置对应的bucket
    public static  <T> T setBucket(String objectName,String value){
        RBucket<Object> bucket = redissonClient.getBucket(objectName);
        bucket.set(value);
        T t= (T) bucket.get(); //值类型由返回值确定
        return  t;
    } 
}

乍一看好像没问题 我写一个静态方法 然后在方法中使用静态变量redissonClient ,哇....,一切看得如此正常

当我开始测试时,NPE.............,我去这是怎么回事,自己在想这不科学啊,怎么会空指针,于是我开始找原因

最后发现是基础不牢啊............,对jvm的类加载机制几乎就没考虑,简要说要错误的原因

jvm在进行类加载的时候,首先会加载类变量,类方法,也就是我这里被static修饰的方法,然后当我调用静态方法进行使用的时候,会使用到redissionClient,注意这个redissionClient是通过autowired进来的,关键问题就在这里,autowired的底层是通过构造器和set方法注入bean的

redissionClient被static修饰 并且还是一个接口 在被调用的时候肯定没有实例化

下面提供三种方式正确使用

方式一


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;
    } 
 
    //根据名字获取map
    public static  <K, V> RMap<K, V> getRMap(String objectName) {
        RMap<K, V> map = redissonClient.getMap(objectName);
        return map;
    }
 
    //根据名字和值设置map
    public static void setMap(String objectName,Object key,Object value){
        RMap<Object, Object> map =redissonClient.getMap(objectName);
        map.put(key,value);
    } 
 
    //根据名字获取set
    public static <V> RSet<V> getSet(String objectName) {
        RSet<V> set = redissonClient.getSet(objectName);
        return set;
    }
 
    //根据名字和值设置set
    public static void setSet(String objectName,Object value){
        RSet<Object> set = redissonClient.getSet(objectName);
        set.add(value);
    }
 
    //根据名字获取list
    public static  <V> RList<V> getRList(String objectName) {
        RList<V> rList = redissonClient.getList(objectName);
        return rList;
    } 
 
    //根据名字和值设置list
    public static void setList(String objectName, int  index,Object element ){
        RList<Object> objectRList = redissonClient.getList(objectName);
        objectRList.set(index,element);
    }
 
    //根据名字获取bucket
    public static <T> RBucket<T> getRBucket(String objectName) {
        RBucket<T> bucket = redissonClient.getBucket(objectName);
        return bucket;
    }
 
    //根据名字和值 设置对应的bucket
    public static  <T> T setBucket(String objectName,String value){
        RBucket<Object> bucket = redissonClient.getBucket(objectName);
        bucket.set(value);
        T t= (T) bucket.get(); //值类型由返回值确定
        return  t;
    } 
}

方式二


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;
    } 
 
    //根据名字获取map
    public static  <K, V> RMap<K, V> getRMap(String objectName) {
        RMap<K, V> map = redissionUtils.redissonClient.getMap(objectName);
        return map;
    }
 
    //根据名字和值设置map
    public static void setMap(String objectName,Object key,Object value){
        RMap<Object, Object> map =redissionUtils.redissonClient.getMap(objectName);
        map.put(key,value);
    } 
 
    //根据名字获取set
    public static <V> RSet<V> getSet(String objectName) {
        RSet<V> set = redissionUtils.redissonClient.getSet(objectName);
        return set;
    }
 
    //根据名字和值设置set
    public static void setSet(String objectName,Object value){
        RSet<Object> set = redissionUtils.redissonClient.getSet(objectName);
        set.add(value);
    }
 
    //根据名字获取list
    public static  <V> RList<V> getRList(String objectName) {
        RList<V> rList = redissionUtils.redissonClient.getList(objectName);
        return rList;
    } 
 
    //根据名字和值设置list
    public static void setList(String objectName, int  index,Object element ){
        RList<Object> objectRList = redissionUtils.redissonClient.getList(objectName);
        objectRList.set(index,element);
    }
 
    //根据名字获取bucket
    public static <T> RBucket<T> getRBucket(String objectName) {
        RBucket<T> bucket = redissionUtils.redissonClient.getBucket(objectName);
        return bucket;
    }
 
    //根据名字和值 设置对应的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(); //值类型由返回值确定
        return  t;
    } 
}

方式三 通过spring上下文获取


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;
 

@Component
@Scope("singleton")
public class SpringUtil implements ApplicationContextAware {
 
    
    private static ApplicationContext applicationContext;
 
    
    @Override
    public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
		SpringUtil.applicationContext = applicationContext;
    }
 
    
    public static ApplicationContext getApplicationContext() {
        return applicationContext;
    }
 
    
    @SuppressWarnings("unchecked")
    public static <T> T getBean(String name) throws BeansException {
        return (T) applicationContext.getBean(name);
    }
 
    
    public static <T> T getBean(Class<T> clz) throws BeansException {
        return (T)applicationContext.getBean(clz);
    }
 
    
    public static boolean containsBean(String name) {
        return applicationContext.containsBean(name);
    }
 
    
    public static boolean isSingleton(String name) throws NoSuchBeanDefinitionException {
        return applicationContext.isSingleton(name);
    }
 
    
    public static Class<?> getType(String name) throws NoSuchBeanDefinitionException {
        return applicationContext.getType(name);
    }
 
    
    public static String[] getAliases(String name) throws NoSuchBeanDefinitionException {
        return applicationContext.getAliases(name);
    } 
 
	
	public static String getJwtToken(HttpServletRequest servletRequest, String tokenId) {
		String token = servletRequest.getHeader(tokenId);
		if (StringUtils.isBlank(token)) {
			token = servletRequest.getParameter(tokenId);
		}
		return token;
	}
}

以上为个人经验,希望能给大家一个参考,也希望大家多多支持编程网。

阅读原文内容投诉

免责声明:

① 本站未注明“稿件来源”的信息均来自网络整理。其文字、图片和音视频稿件的所属权归原作者所有。本站收集整理出于非商业性的教育和科研之目的,并不意味着本站赞同其观点或证实其内容的真实性。仅作为临时的测试数据,供内部测试之用。本站并未授权任何人以任何方式主动获取本站任何信息。

② 本站未注明“稿件来源”的临时测试数据将在测试完成后最终做删除处理。有问题或投稿请发送至: 邮箱/279061341@qq.com QQ/279061341

软考中级精品资料免费领

  • 历年真题答案解析
  • 备考技巧名师总结
  • 高频考点精准押题
  • 2024年上半年信息系统项目管理师第二批次真题及答案解析(完整版)

    难度     813人已做
    查看
  • 【考后总结】2024年5月26日信息系统项目管理师第2批次考情分析

    难度     354人已做
    查看
  • 【考后总结】2024年5月25日信息系统项目管理师第1批次考情分析

    难度     318人已做
    查看
  • 2024年上半年软考高项第一、二批次真题考点汇总(完整版)

    难度     435人已做
    查看
  • 2024年上半年系统架构设计师考试综合知识真题

    难度     224人已做
    查看

相关文章

发现更多好内容

猜你喜欢

AI推送时光机
位置:首页-资讯-后端开发
咦!没有更多了?去看看其它编程学习网 内容吧
首页课程
资料下载
问答资讯