Spring常见问题
Spring 自定义注解
Annotation不支持继承其他接口
Annotation支持三种类型：基本类型、数组类型、枚举类型
default关键字，设置默认值
value属性关键字，当且仅有一个属性时，使用时可省略
/**
* 名 称：OperateType
* 功 能：
* 创 建 人：K.K
* 创建时间：2015/10/21 13:51
* 修 改 人：
* 修改时间：
* 说 明：
* 版 本 号：
*/
public enum OperateType {
NIL(0),
GET(1),
ADD(2),
UPDATE(3),
DELETE(4);
private int value;
private OperateType(int value) {
this.value = value;
}
@Override
public String toString() {
return String.valueOf(this.value);
}
}
import java.lang.annotation.*;
/**
* 名 称：Operation
* 功 能：
* 创 建 人：K.K
* 创建时间：2015/10/21 13:16
* 修 改 人：
* 修改时间：
* 说 明：
* 版 本 号：
*/
@Target({ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
public @interface Operation {
String description() default "";
OperateType type() default OperateType.NIL;
String[] params() default {};
}
@Target描述注解的使用范围
- CONSTRUCTOR 构造器
- FIFLD 域
- LOCAL_VARIABLE 局部变量
METHOD方法- PACKAGE 包
- PARAMETER 参数
- TYPE 类或接口
@Retention注解的生命周期
- SOURCE 在源文件中有效
- CLASS 在class文件中有效
RUNTIME在运行时有效
@Documented允许javadoc将Annotation生成到doc
@Inherited允许子类继承Annotation标记
Spring获取ApplicationContext对象
1. FileSystemXmlApplicationContext
// 重新加载配置文件
ApplicationContext ctx = new FileSystemXmlApplicationContext(...);
2. ClassPathXmlApplicationContext
ApplicationContext ctx = new ClassPathXmlApplication(...);
3. WebApplicationContextUtils
ServletContext servletContext = request.getSession().getServletContext();
// 有可能返回null
ApplicationContext ctx = WebApplicationContextUtils.getWebApplicationContext(servletContext);
4. ContextLoader.getCurrentWebApplicationContext()
5. RequestContextUtils.findWebApplicationContext(..)
6. 创建一个类让其实现org.springframework.context.ApplicationContextAware接口来让Spring在启动的时候为我们注入ApplicationContext对象
Spring中提供一些Aware相关的接口，BeanFactoryAware、 ApplicationContextAware、ResourceLoaderAware、ServletContextAware等等，其中最常用到的是ApplicationContextAware。实现ApplicationContextAware的Bean，在Bean被初始后，将会被注入ApplicationContext的实例。ApplicationContextAware提供了publishEvent()方法，实现Observer(观察者)设计模式的事件传播机，提供了针对Bean的事件传播功能。通过Application.publishEvent方法，我们可以将事件通知系统内所有的ApplicationListener。
Spring事件处理一般过程：
定义Event类，继承org.springframework.context.ApplicationEvent。
编写发布事件类Publisher，实现org.springframework.context.ApplicationContextAware接口。
覆盖方法setApplicationContext(ApplicationContext applicationContext)和发布方法publish(Object obj)。
定义时间监听类EventListener，实现ApplicationListener接口，实现方法onApplicationEvent(ApplicationEvent event)。
@Component
@Lazy(false)
public class Loading implements ApplicationContextAware {
private static ApplicationContext applicationContext;
@Override
public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
this.applicationContext = applicationContext;
}
}
解决Spring中不同配置文件中存在name或者id相同的bean引起的问题
public class DefaultListableBeanFactory extends AbstractAutowireCapableBeanFactory implements ConfigurableListableBeanFactory, BeanDefinitionRegistry, Serializable {
...
private boolean allowBeanDefinitionOverriding = true;
...
public void registerBeanDefinition(String beanName, BeanDefinition beanDefinition) throws BeanDefinitionStoreException {
Assert.hasText(beanName, "Bean name must not be empty");
Assert.notNull(beanDefinition, "BeanDefinition must not be null");
if(beanDefinition instanceof AbstractBeanDefinition) {
try {
((AbstractBeanDefinition)beanDefinition).validate();
} catch (BeanDefinitionValidationException var7) {
throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName, "Validation of bean definition failed", var7);
}
}
Map ex = this.beanDefinitionMap;
synchronized(this.beanDefinitionMap) {
Object oldBeanDefinition = this.beanDefinitionMap.get(beanName);
if(oldBeanDefinition != null) {
if(!this.allowBeanDefinitionOverriding) {
throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName, "Cannot register bean definition [" + beanDefinition + "] for bean \'" + beanName + "\': There is already [" + oldBeanDefinition + "] bound.");
}
if(this.logger.isInfoEnabled()) {
this.logger.info("Overriding bean definition for bean \'" + beanName + "\': replacing [" + oldBeanDefinition + "] with [" + beanDefinition + "]");
}
} else {
this.beanDefinitionNames.add(beanName);
this.frozenBeanDefinitionNames = null;
}
this.beanDefinitionMap.put(beanName, beanDefinition);
}
this.resetBeanDefinition(beanName);
}
public class ContextLoader {
...
/**
* Config param for which {@link ApplicationContextInitializer} classes to use
* for initializing the web application context: {@value}
* @see #customizeContext(ServletContext, ConfigurableWebApplicationContext)
*/
public static final String CONTEXT_INITIALIZER_CLASSES_PARAM = "contextInitializerClasses";
...
/**
* Return the {@link ApplicationContextInitializer} implementation classes to use
* if any have been specified by {@link #CONTEXT_INITIALIZER_CLASSES_PARAM}.
* @param servletContext current servlet context
* @see #CONTEXT_INITIALIZER_CLASSES_PARAM
*/
@SuppressWarnings("unchecked")
protected List<Class<ApplicationContextInitializer<ConfigurableApplicationContext>>>
determineContextInitializerClasses(ServletContext servletContext) {
String classNames = servletContext.getInitParameter(CONTEXT_INITIALIZER_CLASSES_PARAM);
List<Class<ApplicationContextInitializer<ConfigurableApplicationContext>>> classes =
new ArrayList<Class<ApplicationContextInitializer<ConfigurableApplicationContext>>>();
if (classNames != null) {
for (String className : StringUtils.tokenizeToStringArray(classNames, ",")) {
try {
Class<?> clazz = ClassUtils.forName(className, ClassUtils.getDefaultClassLoader());
Assert.isAssignable(ApplicationContextInitializer.class, clazz,
"class [" + className + "] must implement ApplicationContextInitializer");
classes.add((Class<ApplicationContextInitializer<ConfigurableApplicationContext>>)clazz);
}
catch (ClassNotFoundException ex) {
throw new ApplicationContextException(
"Failed to load context initializer class [" + className + "]", ex);
}
}
}
return classes;
}
public class ForbidBeanDefinitionDuplicateContextInitializer implements ApplicationContextInitializer<XmlWebApplicationContext> {
@Override
public void initialize(XmlWebApplicationContext xmlWebApplicationContext) {
xmlWebApplicationContext.setAllowBeanDefinitionOverriding(false);
}
}
<context-param>
<param-name>contextConfigLocation</param-name>
<param-value>classpath:spring-service.xml</param-value>
</context-param>
<context-param>
<param-name>contextInitializerClasses</param-name>
<param-value>com.xxx.xxx.ForbidBeanDefinitionDuplicateContextInitializer</param-value>
</context-param>
<listener>
<listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
</listener>
<servlet>
<servlet-name>basics-orderService</servlet-name>
<servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
<init-param>
<param-name>contextConfigLocation</param-name>
<param-value>classpath:spring-web.xml</param-value>
</init-param>
<init-param>
<param-name>contextInitializerClasses</param-name>
<param-value>com.xxx.xxx.ForbidBeanDefinitionDuplicateContextInitializer</param-value>
</init-param>
<load-on-startup>1</load-on-startup>
</servlet>
BeanFactory与FactoryBean的区别
BeanFactory是IOC容器的基本接口。
FactoryBean一个能产生或者修饰对象生成的工厂Bean，它的实现与设计模式中的工厂模式和修饰器模式类似。
public interface BeanFactory {
/ **
* 用于提取FactoryBean实例并将其区分开来
* 由FactoryBean创建的bean。例如，如果bean命名为myJndiObject是一个FactoryBean，
* 使用＆myJndiObject将返回工厂，而不是工厂返回的实例。
* /
String FACTORY_BEAN_PREFIX = "&";
...
}