前言
本文主要给大家介绍的是关于Spring实现接口动态的相关内容,分享出来供大家参考学习,下面话不多说,来一起看看详细的介绍吧。
关于这个问题是因为领导最近跟我提了一个需求,是有关于实现类Mybatis的@Select、@Insert注解的功能。其是基于interface层面,不存在任何的接口实现类。因而在实现的过程中,首先要解决的是如何动态实现接口的实例化。其次是如何将使接口根据注解实现相应的功能。
声明
解决方案是基于Mybatis源码,进行二次开发实现。
解决方法
我们先来看看Mybatis是如何实现Dao类的扫描的。
MapperScannerConfigurer.java
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
|
public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException { if ( this .processPropertyPlaceHolders) { processPropertyPlaceHolders(); } ClassPathMapperScanner scanner = new ClassPathMapperScanner(registry); scanner.setAddToConfig( this .addToConfig); scanner.setAnnotationClass( this .annotationClass); scanner.setMarkerInterface( this .markerInterface); scanner.setSqlSessionFactory( this .sqlSessionFactory); scanner.setSqlSessionTemplate( this .sqlSessionTemplate); scanner.setSqlSessionFactoryBeanName( this .sqlSessionFactoryBeanName); scanner.setSqlSessionTemplateBeanName( this .sqlSessionTemplateBeanName); scanner.setResourceLoader( this .applicationContext); scanner.setBeanNameGenerator( this .nameGenerator); scanner.registerFilters(); scanner.scan(StringUtils.tokenizeToStringArray( this .basePackage, ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS)); } |
ClassPathMapperScanner是Mybatis继承ClassPathBeanDefinitionScanner类而来的。这里对于ClassPathMapperScanner的配置参数来源于我们在使用Mybatis时的配置而来,是不是还记得在使用Mybatis的时候要配置basePackage的参数呢?
接着我们就顺着scanner.scan()
方法,进入查看一下里面的实现。
ClassPathBeanDefinitionScanner.java
1
2
3
4
5
6
7
8
9
10
11
12
|
public int scan(String... basePackages) { int beanCountAtScanStart = this .registry.getBeanDefinitionCount(); doScan(basePackages); // Register annotation config processors, if necessary. if ( this .includeAnnotationConfig) { AnnotationConfigUtils.registerAnnotationConfigProcessors( this .registry); } return ( this .registry.getBeanDefinitionCount() - beanCountAtScanStart); } |
这里关键的代码是doScan(basePackages);
,那么我们在进去看一下。可能你会看到的是Spring源码的实现方法,但这里Mybatis也实现了自己的一套,我们看一下Mybatis的实现。
ClassPathMapperScanner.java
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
|
public Set<BeanDefinitionHolder> doScan(String... basePackages) { Set<BeanDefinitionHolder> beanDefinitions = super .doScan(basePackages); if (beanDefinitions.isEmpty()) { logger.warn( "No MyBatis mapper was found in '" + Arrays.toString(basePackages) + "' package. Please check your configuration." ); } else { for (BeanDefinitionHolder holder : beanDefinitions) { GenericBeanDefinition definition = (GenericBeanDefinition) holder.getBeanDefinition(); if (logger.isDebugEnabled()) { logger.debug( "Creating MapperFactoryBean with name '" + holder.getBeanName() + "' and '" + definition.getBeanClassName() + "' mapperInterface" ); } // the mapper interface is the original class of the bean // but, the actual class of the bean is MapperFactoryBean definition.getPropertyValues().add( "mapperInterface" , definition.getBeanClassName()); definition.setBeanClass(MapperFactoryBean. class ); definition.getPropertyValues().add( "addToConfig" , this .addToConfig); boolean explicitFactoryUsed = false ; if (StringUtils.hasText( this .sqlSessionFactoryBeanName)) { definition.getPropertyValues().add( "sqlSessionFactory" , new RuntimeBeanReference( this .sqlSessionFactoryBeanName)); explicitFactoryUsed = true ; } else if ( this .sqlSessionFactory != null ) { definition.getPropertyValues().add( "sqlSessionFactory" , this .sqlSessionFactory); explicitFactoryUsed = true ; } if (StringUtils.hasText( this .sqlSessionTemplateBeanName)) { if (explicitFactoryUsed) { logger.warn( "Cannot use both: sqlSessionTemplate and sqlSessionFactory together. sqlSessionFactory is ignored." ); } definition.getPropertyValues().add( "sqlSessionTemplate" , new RuntimeBeanReference( this .sqlSessionTemplateBeanName)); explicitFactoryUsed = true ; } else if ( this .sqlSessionTemplate != null ) { if (explicitFactoryUsed) { logger.warn( "Cannot use both: sqlSessionTemplate and sqlSessionFactory together. sqlSessionFactory is ignored." ); } definition.getPropertyValues().add( "sqlSessionTemplate" , this .sqlSessionTemplate); explicitFactoryUsed = true ; } if (!explicitFactoryUsed) { if (logger.isDebugEnabled()) { logger.debug( "Enabling autowire by type for MapperFactoryBean with name '" + holder.getBeanName() + "'." ); } definition.setAutowireMode(AbstractBeanDefinition.AUTOWIRE_BY_TYPE); } } } return beanDefinitions; } |
definition.setBeanClass(MapperFactoryBean.class);
这行代码是非常关键的一句,由于在Spring中存在两种自动实例化的方式,一种是我们常用的本身的接口实例化类进行接口实例化,还有一种就是这里的自定义实例化。而这里的setBeanClass方法就是在BeanDefinitionHolder中进行配置。在Spring进行实例化的时候进行处理。
那么我们在看一下MapperFactoryBean.class
MapperFactoryBean.java
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
|
public class MapperFactoryBean<T> extends SqlSessionDaoSupport implements FactoryBean<T> { private Class<T> mapperInterface; private boolean addToConfig = true ; /** * Sets the mapper interface of the MyBatis mapper * * @param mapperInterface class of the interface */ public void setMapperInterface(Class<T> mapperInterface) { this .mapperInterface = mapperInterface; } /** * If addToConfig is false the mapper will not be added to MyBatis. This means * it must have been included in mybatis-config.xml. * <p> * If it is true, the mapper will be added to MyBatis in the case it is not already * registered. * <p> * By default addToCofig is true. * * @param addToConfig */ public void setAddToConfig( boolean addToConfig) { this .addToConfig = addToConfig; } /** * {@inheritDoc} */ @Override protected void checkDaoConfig() { super .checkDaoConfig(); notNull( this .mapperInterface, "Property 'mapperInterface' is required" ); Configuration configuration = getSqlSession().getConfiguration(); if ( this .addToConfig && !configuration.hasMapper( this .mapperInterface)) { try { configuration.addMapper( this .mapperInterface); } catch (Throwable t) { logger.error( "Error while adding the mapper '" + this .mapperInterface + "' to configuration." , t); throw new IllegalArgumentException(t); } finally { ErrorContext.instance().reset(); } } } /** * {@inheritDoc} */ public T getObject() throws Exception { return getSqlSession().getMapper( this .mapperInterface); } /** * {@inheritDoc} */ public Class<T> getObjectType() { return this .mapperInterface; } /** * {@inheritDoc} */ public boolean isSingleton() { return true ; } |
在该类中其实现了FactoryBean接口,看过Spring源码的人,我相信对其都有很深的印象,其在Bean的实例化中起着很重要的作用。在该类中我们要关注的是getObject方法,我们之后将动态实例化的接口对象放到Spring实例化列表中,这里就是入口,也是我们的起点。不过要特别说明的是mapperInterface的值是如何被赋值的,可能会有疑问,我们再来看看上面的ClassPathMapperScanner.java我们在配置MapperFactoryBean.class的上面存在一行 definition.getPropertyValues().add("mapperInterface", definition.getBeanClassName());
其在之后在Spring的PostProcessorRegistrationDelegate类的populateBean方法中进行属性配置,会将其依靠反射的方式将其注入到MapperFactoryBean.class中。
而且definition.getPropertyValues().add
中添加的值是注入到MapperFactoryBean对象中去的。这一点需要说明一下。
总结
以上就是这篇文章的全部内容了,希望本文的内容对大家的学习或者工作能带来一定的帮助,如果有疑问大家可以留言交流,谢谢大家对服务器之家的支持。
原文链接:https://segmentfault.com/a/1190000010366382