Spring框架简介

1. Spring框架的作用

轻量:Spring是轻量级的,基本的版本大小为2MB
控制反转:Spring通过控制反转实现了松散耦合,对象们给出它们的依赖,而不是创建或查找依赖的对象们。
面向切面的编程AOP:Spring支持面向切面的编程,并且把应用业务逻辑和系统服务分开。
容器:Spring包含并管理应用中对象的生命周期和配置
MVC框架: Spring-MVC
事务管理:Spring提供一个持续的事务管理接口,可以扩展到上至本地事务下至全局事务JTA
异常处理:Spring提供方便的API把具体技术相关的异常

tx:annotation-driven注解方式EnableTransactionManagement

替换方法是用@EnableTransactionManagement

以下是官方文档:

org.springframework.transaction.annotation
Annotation Type EnableTransactionManagement


@Target(value=TYPE)
@Retention(value=RUNTIME)
@Documented
@Import(value=TransactionManagementConfigurationSelector.class)
public @interface EnableTransactionManagement

Enables Spring’s annotation-driven transaction management capability, similar to the support found in Spring’s <tx:*> XML namespace. To be used on @Configuration classes as follows:

 @Configuration
 @EnableTransactionManagement
 public class AppConfig {
     @Bean
     public FooRepository fooRepository() {
         // configure and return a class having @Transactional methods
         return new JdbcFooRepository(dataSource());
     }

     @Bean
     public DataSource dataSource() {
         // configure and return the necessary JDBC DataSource
     }

     @Bean
     public PlatformTransactionManager txManager() {
         return new DataSourceTransactionManager(dataSource());
     }
 }

For reference, the example above can be compared to the following Spring XML configuration:

 <beans>
     <tx:annotation-driven/>
     <bean id="fooRepository" class="com.foo.JdbcFooRepository">
         <constructor-arg ref="dataSource"/>
     </bean>
     <bean id="dataSource" class="com.vendor.VendorDataSource"/>
     <bean id="transactionManager" class="org.sfwk...DataSourceTransactionManager">
         <constructor-arg ref="dataSource"/>
     </bean>
 </beans>
 

In both of the scenarios above, @EnableTransactionManagement and <tx:annotation-driven/> are responsible for registering the necessary Spring components that power annotation-driven transaction management, such as the TransactionInterceptor and the proxy- or AspectJ-based advice that weave the interceptor into the call stack when JdbcFooRepository‘s @Transactional methods are invoked.

A minor difference between the two examples lies in the naming of the PlatformTransactionManager bean: In the @Bean case, the name is “txManager” (per the name of the method); in the XML case, the name is“transactionManager”. The <tx:annotation-driven/> is hard-wired to look for a bean named “transactionManager” by default, however @EnableTransactionManagement is more flexible; it will fall back to a by-type lookup for anyPlatformTransactionManager bean in the container. Thus the name can be “txManager”, “transactionManager”, or “tm”: it simply does not matter.

For those that wish to establish a more direct relationship between @EnableTransactionManagement and the exact transaction manager bean to be used, the TransactionManagementConfigurer callback interface may be implemented – notice the implements clause and the @Override-annotated method below:

 @Configuration
 @EnableTransactionManagement
 public class AppConfig implements TransactionManagementConfigurer {
     @Bean
     public FooRepository fooRepository() {
         // configure and return a class having @Transactional methods
         return new JdbcFooRepository(dataSource());
     }

     @Bean
     public DataSource dataSource() {
         // configure and return the necessary JDBC DataSource
     }

     @Bean
     public PlatformTransactionManager txManager() {
         return new DataSourceTransactionManager(dataSource());
     }

     @Override
     public PlatformTransactionManager annotationDrivenTransactionManager() {
         return txManager();
     }
 }

This approach may be desirable simply because it is more explicit, or it may be necessary in order to distinguish between two PlatformTransactionManager beans present in the same container. As the name suggests, theannotationDrivenTransactionManager() will be the one used for processing @Transactional methods. See TransactionManagementConfigurer Javadoc for further details.

The mode() attribute controls how advice is applied; if the mode is AdviceMode.PROXY (the default), then the other attributes control the behavior of the proxying.

If the mode() is set to AdviceMode.ASPECTJ, then the proxyTargetClass() attribute is obsolete. Note also that in this case the spring-aspects module JAR must be present on the classpath.

Since:
3.1
Author:
Chris Beams
See Also:
TransactionManagementConfigurer, TransactionManagementConfigurationSelector, ProxyTransactionManagementConfiguration, AspectJTransactionManagementConfiguration

Optional Element Summary
 AdviceMode mode
Indicate how transactional advice should be applied.
 int order
Indicate the ordering of the execution of the transaction advisor when multiple advices are applied at a specific joinpoint.
 boolean proxyTargetClass
Indicate whether subclass-based (CGLIB) proxies are to be created (true) as opposed to standard Java interface-based proxies (false).

 

proxyTargetClass

public abstract boolean proxyTargetClass
Indicate whether subclass-based (CGLIB) proxies are to be created (true) as opposed to standard Java interface-based proxies (false). The default is false. Applicable only if mode() is set to AdviceMode.PROXY.Note that setting this attribute to true will affect all Spring-managed beans requiring proxying, not just those marked with @Transactional. For example, other beans marked with Spring’s @Async annotation will be upgraded to subclass proxying at the same time. This approach has no negative impact in practice unless one is explicitly expecting one type of proxy vs another, e.g. in tests.

Default:
false

mode

public abstract AdviceMode mode
Indicate how transactional advice should be applied. The default is AdviceMode.PROXY.
See Also:
AdviceMode
Default:
org.springframework.context.annotation.AdviceMode.PROXY

order

public abstract int order
Indicate the ordering of the execution of the transaction advisor when multiple advices are applied at a specific joinpoint. The default is Ordered.LOWEST_PRECEDENCE.
Default:
2147483647

 

https://docs.spring.io/spring/docs/4.0.x/javadoc-api/org/springframework/transaction/annotation/EnableTransactionManagement.html

更多文档:

https://docs.spring.io/spring/docs/4.0.x/javadoc-api/overview-summary.html

Nginx使用upstream模块实现tomcat负载均衡

UPSTREAM负载均衡模块

负载均衡模块用于从”upstream”指令定义的后端主机列表中选取一台主机。nginx先使用负载均衡模块找到一台主机,再使用upstream模块实现与这台主机的交互。为了方便介绍负载均衡模块,做到言之有物,以下选取nginx内置的ip hash模块作为实际例子进行分析。

配置

要了解负载均衡模块的开发方法,首先需要了解负载均衡模块的使用方法。因为负载均衡模块与之前书中提到的模块差别比较大,所以我们从配置入手比较容易理解。

在配置文件中,我们如果需要使用ip hash的负载均衡算法。我们需要写一个类似下面的配置:

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