在SpringBoot中注入RedisTemplate实例异常的解决方案

注入redistemplate实例异常

最近，在项目开发过程中使用了redistemplate，进行单元测试时提示

field redistemplate in com.example.demo1.dao.redisdao required a bean of type ‘org.springframework.data.redis.core.redistemplate’ that could not be found

翻译过来就是“找不到类型为redistemplate的bean”。

当然，仅看这句话我们无法确定为什么会出现这个问题。

贴出详细的错误日志

2018-08-10 14:53:49.761 - caught exception while allowing testexecutionlistener [org.springframework.test.context.web.servlettestexecutionlistener@5af3afd9] to prepare test instance [com.example.demo1.demo1applicationtests@2361365c]
java.lang.illegalstateexception: failed to load applicationcontext
    at org.springframework.test.context.cache.defaultcacheawarecontextloaderdelegate.loadcontext(defaultcacheawarecontextloaderdelegate.java:124)
    at org.springframework.test.context.support.defaulttestcontext.getapplicationcontext(defaulttestcontext.java:83)
    at org.springframework.test.context.web.servlettestexecutionlistener.setuprequestcontextifnecessary(servlettestexecutionlistener.java:189)
    at org.springframework.test.context.web.servlettestexecutionlistener.preparetestinstance(servlettestexecutionlistener.java:131)
    at org.springframework.test.context.testcontextmanager.preparetestinstance(testcontextmanager.java:230)
    at org.springframework.test.context.junit4.springjunit4classrunner.createtest(springjunit4classrunner.java:228)
    at org.springframework.test.context.junit4.springjunit4classrunner$1.runreflectivecall(springjunit4classrunner.java:287)
    at org.junit.internal.runners.model.reflectivecallable.run(reflectivecallable.java:12)
    at org.springframework.test.context.junit4.springjunit4classrunner.methodblock(springjunit4classrunner.java:289)
    at org.springframework.test.context.junit4.springjunit4classrunner.runchild(springjunit4classrunner.java:247)
    at org.springframework.test.context.junit4.springjunit4classrunner.runchild(springjunit4classrunner.java:94)
    at org.junit.runners.parentrunner$3.run(parentrunner.java:290)
    at org.junit.runners.parentrunner$1.schedule(parentrunner.java:71)
    at org.junit.runners.parentrunner.runchildren(parentrunner.java:288)
    at org.junit.runners.parentrunner.access$000(parentrunner.java:58)
    at org.junit.runners.parentrunner$2.evaluate(parentrunner.java:268)
    at org.springframework.test.context.junit4.statements.runbeforetestclasscallbacks.evaluate(runbeforetestclasscallbacks.java:61)
    at org.springframework.test.context.junit4.statements.runaftertestclasscallbacks.evaluate(runaftertestclasscallbacks.java:70)
    at org.junit.runners.parentrunner.run(parentrunner.java:363)
    at org.springframework.test.context.junit4.springjunit4classrunner.run(springjunit4classrunner.java:191)
    at org.eclipse.jdt.internal.junit4.runner.junit4testreference.run(junit4testreference.java:86)
    at org.eclipse.jdt.internal.junit.runner.testexecution.run(testexecution.java:38)
    at org.eclipse.jdt.internal.junit.runner.remotetestrunner.runtests(remotetestrunner.java:459)
    at org.eclipse.jdt.internal.junit.runner.remotetestrunner.runtests(remotetestrunner.java:675)
    at org.eclipse.jdt.internal.junit.runner.remotetestrunner.run(remotetestrunner.java:382)
    at org.eclipse.jdt.internal.junit.runner.remotetestrunner.main(remotetestrunner.java:192)
caused by: org.springframework.beans.factory.unsatisfieddependencyexception: error creating bean with name 'redisdao': unsatisfied dependency expressed through field 'redistemplate'; nested exception is org.springframework.beans.factory.nosuchbeandefinitionexception: no qualifying bean of type 'org.springframework.data.redis.core.redistemplate<java.lang.string, java.lang.object>' available: expected at least 1 bean which qualifies as autowire candidate. dependency annotations: {@org.springframework.beans.factory.annotation.autowired(required=true)}
    at org.springframework.beans.factory.annotation.autowiredannotationbeanpostprocessor$autowiredfieldelement.inject(autowiredannotationbeanpostprocessor.java:588)
    at org.springframework.beans.factory.annotation.injectionmetadata.inject(injectionmetadata.java:88)
    at org.springframework.beans.factory.annotation.autowiredannotationbeanpostprocessor.postprocesspropertyvalues(autowiredannotationbeanpostprocessor.java:366)
    at org.springframework.beans.factory.support.abstractautowirecapablebeanfactory.populatebean(abstractautowirecapablebeanfactory.java:1264)
    at org.springframework.beans.factory.support.abstractautowirecapablebeanfactory.docreatebean(abstractautowirecapablebeanfactory.java:553)
    at org.springframework.beans.factory.support.abstractautowirecapablebeanfactory.createbean(abstractautowirecapablebeanfactory.java:483)
    at org.springframework.beans.factory.support.abstractbeanfactory$1.getobject(abstractbeanfactory.java:306)
    at org.springframework.beans.factory.support.defaultsingletonbeanregistry.getsingleton(defaultsingletonbeanregistry.java:230)
    at org.springframework.beans.factory.support.abstractbeanfactory.dogetbean(abstractbeanfactory.java:302)
    at org.springframework.beans.factory.support.abstractbeanfactory.getbean(abstractbeanfactory.java:197)
    at org.springframework.beans.factory.support.defaultlistablebeanfactory.preinstantiatesingletons(defaultlistablebeanfactory.java:761)
    at org.springframework.context.support.abstractapplicationcontext.finishbeanfactoryinitialization(abstractapplicationcontext.java:867)
    at org.springframework.context.support.abstractapplicationcontext.refresh(abstractapplicationcontext.java:543)
    at org.springframework.boot.springapplication.refresh(springapplication.java:693)
    at org.springframework.boot.springapplication.refreshcontext(springapplication.java:360)
    at org.springframework.boot.springapplication.run(springapplication.java:303)
    at org.springframework.boot.test.context.springbootcontextloader.loadcontext(springbootcontextloader.java:120)
    at org.springframework.test.context.cache.defaultcacheawarecontextloaderdelegate.loadcontextinternal(defaultcacheawarecontextloaderdelegate.java:98)
    at org.springframework.test.context.cache.defaultcacheawarecontextloaderdelegate.loadcontext(defaultcacheawarecontextloaderdelegate.java:116)
    ... 25 common frames omitted
caused by: org.springframework.beans.factory.nosuchbeandefinitionexception: no qualifying bean of type 'org.springframework.data.redis.core.redistemplate<java.lang.string, java.lang.object>' available: expected at least 1 bean which qualifies as autowire candidate. dependency annotations: {@org.springframework.beans.factory.annotation.autowired(required=true)}
    at org.springframework.beans.factory.support.defaultlistablebeanfactory.raisenomatchingbeanfound(defaultlistablebeanfactory.java:1493)
    at org.springframework.beans.factory.support.defaultlistablebeanfactory.doresolvedependency(defaultlistablebeanfactory.java:1104)
    at org.springframework.beans.factory.support.defaultlistablebeanfactory.resolvedependency(defaultlistablebeanfactory.java:1066)
    at org.springframework.beans.factory.annotation.autowiredannotationbeanpostprocessor$autowiredfieldelement.inject(autowiredannotationbeanpostprocessor.java:585)
    ... 43 common frames omitted

看到这一大段错误日志是不是有点晕，其实我们只需要看关键的错误日志就可以定位到问题。

错误日志中的第二个caused by打印了关键的错误日志：

no qualifying bean of type ‘org.springframework.data.redis.core.redistemplate< java.lang.string, java.lang.object>

笔主回看写的代码，在注入redistemplate< k, v>时指定了具体的类型。

@component
public class redisdao {
    /**
     * 注入时指定了k、v类型
     */
    @autowired
    private redistemplate<string, object> redistemplate;
    @autowired
    private stringredistemplate stringredistemplate;
    @resource(name="redistemplate")
    valueoperations<string, object> valopsobj;
    @resource(name="stringredistemplate")
    valueoperations<string, string> valopsstr;  
}

根据错误日志查看defaultlistablebeanfactory这个类的第1493行的代码，源码如下：

   /**
     * 为无法解决的依赖抛出nosuchbeandefinitionexception或beannotofrequiredtypeexception。
     * raise a nosuchbeandefinitionexception or beannotofrequiredtypeexception
     * for an unresolvable dependency.
     */
    private void raisenomatchingbeanfound(
            class<?> type, resolvabletype resolvabletype, dependencydescriptor descriptor) throws beansexception {
        checkbeannotofrequiredtype(type, descriptor);
        //抛出nosuchbeandefinitionexception
        throw new nosuchbeandefinitionexception(resolvabletype,
                "expected at least 1 bean which qualifies as autowire candidate. " +
                "dependency annotations: " + objectutils.nullsafetostring(descriptor.getannotations()));
    }
   /**
     * 为无法解决的依赖抛出beannotofrequiredtypeexception，如果适用，例如，bean的目标类型匹配但是公开的代理不匹配。
     * 
     * 
     * raise a beannotofrequiredtypeexception for an unresolvable dependency, if applicable,
     * i.e. if the target type of the bean would match but an exposed proxy doesn't.
     */
    private void checkbeannotofrequiredtype(class<?> type, dependencydescriptor descriptor) {
        for (string beanname : this.beandefinitionnames) {
            rootbeandefinition mbd = getmergedlocalbeandefinition(beanname);
            class<?> targettype = mbd.gettargettype();
            if (targettype != null && type.isassignablefrom(targettype) &&
                    isautowirecandidate(beanname, mbd, descriptor, getautowirecandidateresolver())) {
                // probably a proxy interfering with target type match -> throw meaningful exception.
                object beaninstance = getsingleton(beanname, false);
                class<?> beantype = (beaninstance != null ? beaninstance.getclass() : predictbeantype(beanname, mbd));
                if (!type.isassignablefrom((beantype))) {
                    //抛出beannotofrequiredtypeexception
                    throw new beannotofrequiredtypeexception(beanname, type, beantype);
                }
            }
        }
        beanfactory parent = getparentbeanfactory();
        if (parent instanceof defaultlistablebeanfactory) {
            ((defaultlistablebeanfactory) parent).checkbeannotofrequiredtype(type, descriptor);
        }
    }

这两个方法说明了没有找到redistemplate< string, object>可以匹配的bean，那么这个问题该如何解决呢？不妨在使用redistemplate< k, v>时不指定具体的类型，修改代码如下：

/**
 * 注入时不指定k、v的类型 
 */
@autowired
private redistemplate redistemplate;

重新启动服务，启动日志没有报错，redistemplate注入bean成功了。

为什么redistemplate< string, object>注入bean会失败呢，很是纳闷。思考很久，想到redistemplate在springboot框架中是自动配置的，容器中默认的就是redistemplate的实例。

想到这里，就需要翻下官网的文档，看看官网文档有没有什么说明。果然，官方文档第30.1.1章节还是针对redistemplate做了说明。

官方文档地址：https://docs.spring.io/spring-boot/docs/current/reference/htmlsingle/

if you add your own @bean of any of the auto-configured types, it replaces the default (except in the case of redistemplate, when the exclusion is based on the bean name, redistemplate, not its type). 

如果针对自动配置类型添加自己的bean，它将取代默认的。我的代码好像写的没问题啊，等等…括号中这句话才是重点啊。翻译一波，在redistemplate的情况下除外，当排除基于bean的名称，而不是它的类型。英文不太好，怎么翻译好像都不大通顺。

现在好像明白了，刚才的redistemplate< string, object>注入时用到了@autowired，@autowired默认按照类型装配的。也就是说，想要获取redistemplate< string, object>的bean，要根据名字装配。那么自然想到使用@resource，它默认按照名字装配。

再次修改代码如下：

   /**
     * 注入时指定了k、v类型
     */
    @resource
    private redistemplate<string, object> redistemplate;

再次重新启动服务，启动日志没有报错，redistemplate< string, object>注入bean成功了。通过这个错误，学习到springboot框架中自动配置类的一个特性。同时，也反映出学习一门技术要从官网开始，避免踩坑。

在实际开发过程中，使用redistemplate< k, v>不是必须指定k、v的类型，使用默认的bean就能满足需求。

最后想再验证一个小的问题

再次修改代码如下：

/**
 * redis访问工具类
 * @author zhaoheng
 * @date   2018年8月10日
 */
@component
public class redisdao {
    /**
     * 注入时指定k、v类型都为string
     */
    @autowired
    private redistemplate<string, string> redistemplate;
    @autowired
    private stringredistemplate stringredistemplate;
    /**
     * 比较两个对象是否是同一个对象
     */
    public boolean compare () {
        log.info("redistemplate的hashcode：{}", redistemplate.hashcode());
        log.info("stringredistemplate的hashcode：{}", stringredistemplate.hashcode());
        log.info("equal()的结果：{}", redistemplate.equals(stringredistemplate));
        return redistemplate == stringredistemplate;
    }   
}
/**
 * 单元测试类
 * @author zhaoheng
 * @date   2018年8月10日
 */
@runwith(springrunner.class)
@springboottest
public class demo1applicationtests {
    private static final logger log = loggerfactory.getlogger(demo1applicationtests.class);
    @autowired
    private redisdao redisdao;
    @test
    public void contextloads() {
        boolean flag = redisdao.compare();
        log.info("redistemplate和stringredistemplate的比较结果：{}", flag);
    }
}

上边这段代码在注入redistemplate时指定k、v都为string类型，在compare()方法中比较redistemplate和stringredistemplate是否是同一个对象。运行下单元测试类，测试结果如下：

2018-08-10 18:30:57.075 - started demo1applicationtests in 15.58 seconds (jvm running for 16.974)
2018-08-10 18:30:57.360 - redistemplate的hashcode：1996087296
2018-08-10 18:30:57.360 - stringredistemplate的hashcode：1996087296
2018-08-10 18:30:57.363 - equal()的结果：true
2018-08-10 18:30:57.364 - redistemplate和stringredistemplate的比较结果：true

测试结果表明redistemplate和stringredistemplate是同一个对象。等等…这次注入redistemplate时指定k、v都为string为什么没有错呢？而且，两个对象竟然是同一个对象。还是来看下stringredistemplate的源码吧。

public class stringredistemplate extends redistemplate<string, string> {
    /**
     * constructs a new <code>stringredistemplate</code> instance. {@link #setconnectionfactory(redisconnectionfactory)}
     * and {@link #afterpropertiesset()} still need to be called.
     */
    public stringredistemplate() {
        redisserializer<string> stringserializer = new stringredisserializer();
        setkeyserializer(stringserializer);
        setvalueserializer(stringserializer);
        sethashkeyserializer(stringserializer);
        sethashvalueserializer(stringserializer);
    }
    /**
     * constructs a new <code>stringredistemplate</code> instance ready to be used.
     * 
     * @param connectionfactory connection factory for creating new connections
     */
    public stringredistemplate(redisconnectionfactory connectionfactory) {
        this();
        setconnectionfactory(connectionfactory);
        afterpropertiesset();
    }
    protected redisconnection preprocessconnection(redisconnection connection, boolean existingconnection) {
        return new defaultstringredisconnection(connection);
    }
}

看了源码是不是理解了，因为stringredistemplate类的父类就是redistemplate< string, string>，而bean默认是单例的，两个是自然是同一个对象了。

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。