ClasspathScanningAnnotationSessionFactoryBean自动包装配

Spring 2.5以上 提倡使用 annotation 的方式取代 xml 的设定，这个部分几乎完全取代了 Spring Annotations 的功能，看來这个 project 应该已经沒有什么生存空间。但 spring annotations 的 hibernate module 所提供的 AutomaticAnnotationSessionFactoryBean 是一个很不错的功能。以往使用 Hibernate Annotations 时我们只能以 fully qualifiedclass name 或 fully qualified 的 package name 來指定 entity class。通过 AutomaticAnnotationSessionFactoryBean 我们可以自动找到所有标识为 @javax.persistence.Entity 的 classes 自动加入到 hibernate 的 mapping classes。Spring 2.5 既然本身就可以自动搜寻到 @Component 以及相关的 bean class，那我们就应该做到@Entity 的自动搜索。我按照 spring annotations 的做法，提供一个自製的 session factory bean：

import org.hibernate.HibernateException;

import org.hibernate.cfg.AnnotationConfiguration;

import org.springframework.core.io.Resource;

import org.springframework.core.io.support.PathMatchingResourcePatternResolver;

import org.springframework.core.io.support.ResourcePatternResolver;

import org.springframework.core.type.classreading.CachingMetadataReaderFactory;

import org.springframework.core.type.classreading.MetadataReader;

import org.springframework.core.type.classreading.MetadataReaderFactory;

import org.springframework.core.type.filter.AnnotationTypeFilter;

import org.springframework.core.type.filter.TypeFilter;

import org.springframework.orm.hibernate3.annotation.AnnotationSessionFactoryBean;

import org.springframework.util.ClassUtils;

import javax.persistence.Entity;

import java.io.IOException;

/**

* Created on: 2007/11/24

*

* @author Alan She

*/

public class ClasspathScanningAnnotationSessionFactoryBean extends AnnotationSessionFactoryBean {

private static final String DEFAULT_RESOURCE_PATTERN = "**/*.class";

private ResourcePatternResolver resourcePatternResolver = new PathMatchingResourcePatternResolver();

private MetadataReaderFactory metadataReaderFactory = new CachingMetadataReaderFactory(this.resourcePatternResolver);

private final TypeFilter entityFilter = new AnnotationTypeFilter(Entity.class);

private String resourcePattern = DEFAULT_RESOURCE_PATTERN;

private String[] basePackages;

public void setBasePackages(String basePackages) {

this.basePackages = basePackages;

}

protected void postProcessAnnotationConfiguration(AnnotationConfiguration config) throws HibernateException {

for (String basePackage : basePackages) {

try {

String packageSearchPath = ResourcePatternResolver.CLASSPATH_ALL_URL_PREFIX +

ClassUtils.convertClassNameToResourcePath(basePackage) + "/" + this.resourcePattern;

Resource[] resources = this.resourcePatternResolver.getResources(packageSearchPath);

for (int i = 0; i < resources.length; i++) {

Resource resource = resources[i];

MetadataReader metadataReader = this.metadataReaderFactory.getMetadataReader(resource);

if (isEntity(metadataReader)) {

String classFileFullPath = resource.getURL().getPath();

String basePackageResourcePath = ClassUtils.convertClassNameToResourcePath(basePackage);

int startIndex = classFileFullPath.indexOf(basePackageResourcePath);

final String classFilePath = classFileFullPath.substring(startIndex,

classFileFullPath.length() - ClassUtils.CLASS_FILE_SUFFIX.length());

Class entityClass = null;

try {

entityClass = ClassUtils.forName(ClassUtils.convertResourcePathToClassName(classFilePath));

} catch (ClassNotFoundException e) {

throw new HibernateException("Entity class not found during classpath scanning", e);

}

config.addAnnotatedClass(entityClass);

}

}

}

catch (IOException ex) {

throw new HibernateException("I/O failure during classpath scanning", ex);

}

}

}

private boolean isEntity(MetadataReader metadataReader) throws IOException {

if (entityFilter.match(metadataReader, this.metadataReaderFactory)) {

return true;

}

return false;

}

}

这个 class 的內容是以 Spring 2.5 的 ClassPathBeanDefinitionScanner 为骨干而來的。原理很简单，以 PathMatchingResourcePatternResolver 去找到所以 basePackage 下的 classes，一一比對是否有 annotate 了 @javax.persistence.Entity，如果有就加入到 session factory 的 annotationClass。[/code]

<bean id="sessionFactory" class="com.hibernate.ClasspathScanningAnnotationSessionFactoryBean"><property name="dataSource" ref="dataSource"/><property name="hibernateProperties"><props><prop key="hibernate.dialect">${hibernate.dialect}</prop></props></property><property name="basePackages"><list><value>package.model</value></list></property></bean>

[/code]

[/code]使用上也非常简单，跟一般 spring 宣告 session factory 一样，只需指定 basePackage 作为搜寻的范围即可。自动搜寻有优点也有缺点，但一个个的去设定 entity 很很麻烦。有人可能会觉得万一如果我有在 classpath 里的 entity 又不想加入那不就只能全都用手动设定？其实如果想要有些弹性可以加入 include / exclude pattern 等东西，让设定更活。毕竟设定当时代已经慢慢过去，在 convention over configuration 的大趋勢之下，想办法制定规则以及將规则以自动化落实才是长久之计。