Spring對(duì)靜態(tài)變量無(wú)法注入的解決方案
Spring對(duì)靜態(tài)變量無(wú)法注入
問(wèn)題
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();
}
}
set方法注入
注解方式
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;
}
xml方式
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>
@PostConstruct注解方式注入
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>
靜態(tài)方法注入bean失敗原因
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
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;
}
}
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;
}
}
方式三 通過(guò)spring上下文獲取
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;
/**
* 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;
}
}
以上為個(gè)人經(jīng)驗(yàn),希望能給大家一個(gè)參考,也希望大家多多支持腳本之家。
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