Shulou(Shulou.com)06/02 Report--

Today, I will talk to you about how to solve the problem that the transaction configuration does not take effect caused by the expansion of the scanning scope of the package by SpringMVC. Many people may not know much about it. In order to make you understand better, the editor has summarized the following for you. I hope you can get something according to this article.

When integrating the new ssh framework, spring+springmvc+hibernate found a problem, that is, when the persistence layer uses hibernateTemplate, it does not automatically commit the transaction. After the scanning range of the package by SpringMVC is expanded, the transaction configuration does not take effect.

The first thing to configure is the initialized loaded application file of the Spring container, and then the front controller (DispatchServlet) of the SpringMVC. When the DispatchServlet is configured, a new container will be created in the Spring container.

These are actually two containers, Spring as the parent container and SpringMVC as the child container

Configuration of Spring in web.xml

Org.springframework.web.context.ContextLoaderListener contextConfigLocation classpath:/applicationContext.xml spring org.springframework.web.servlet.DispatcherServlet 1 spring /

ApplicationContext.xml uses AOP declarative transaction configuration

The problem encountered is that after executing the save method through Hibernate, the data cannot be inserted into the DB and the console does not print out the SQL (there is no output from the console)

After careful investigation and reading the online article, we found that the problem appeared in spring-servlet.xml:

The result of the above configuration is that SpringMVC scans and loads all package of Service and Dao

Problem analysis:

1. Spring and SpringMVC belong to the parent-child container relationship. When the framework starts, start the Spring container first, and then start the SpringMVC container. The child container can access the Bean in the parent container, but the parent container cannot access the Bean in the child container

2. Because SpringMVC expands the scope of scanning and loads instances of the class identified by @ Service, the Controller layer actually injects Service instances in the child container when injecting Service.

3. The transaction is configured in the parent container, and the Spring parent container applies the transaction configuration when loading the Service, while SpringMVC only loads the instance of Service.

The solution is as follows

ApplicationContext.xml sweeps the bag and excludes Controller

Springmvc.xml scan package scan only controller

Springmvc configuration file use-default-filters= "false", because the default value of use-default-filters is true, that is, all packages with @ Controller, @ Service and other annotations are scanned, and then only controller is scanned.

Further proof of printing container-managed bean names

We have SpringMVC scan Controller and Service,Spring scan Service and DAO.

Print the bean name managed by the parent-child window using the following code:

WebApplicationContext webApplicationContext = WebApplicationContextUtils.getWebApplicationContext (request.getSession (). GetServletContext ()); String [] definationBeanNames = webApplicationContext.getBeanNamesForAnnotation (Service.class); List names = new ArrayList (Arrays.asList (definationBeanNames)); Collections.addAll (names, webApplicationContext.getBeanNamesForAnnotation (Controller.class)); Collections.addAll (names, webApplicationContext.getBeanNamesForAnnotation (Repository.class)); System.out.println ("Bean managed by Spring parent container:") For (String beanName: names) {System.out.println (beanName);} webApplicationContext = RequestContextUtils.getWebApplicationContext (request); definationBeanNames = webApplicationContext.getBeanNamesForAnnotation (Service.class); names = new ArrayList (Arrays.asList (definationBeanNames)); Collections.addAll (names, webApplicationContext.getBeanNamesForAnnotation (Controller.class)); Collections.addAll (names, webApplicationContext.getBeanNamesForAnnotation (Repository.class)) System.out.println ("SpringMVC sub-container managed Bean:"); for (String beanName: names) {System.out.println (beanName);}

We found that the parent and child containers also maintain instances of classes in the Service layer, and should be two separate instances.

Use only child containers, not parent containers at all

Now let's test another scenario.

Comment out ContextLoaderListener in web.xml and modify the configuration to:

Spring org.springframework.web.servlet.DispatcherServlet contextConfigLocation classpath:/applicationContext.xml;/WEB-INF/spring-servlet.xml 1 spring /

The parent container is removed and all configuration files are loaded by SpringMVC.

The print result is as follows:

1. When the transaction is managed by Spring, Spring is responsible for managing the opening, closing, flush and other steps of the transaction in session. Developers only need to call methods such as save and update.

2. When there is a parent-child container in the web project framework, and the transaction is managed by the parent container, you should pay attention to the scope of SpringMVC scanning the package and only scan the Controller components. Official recommendation: father-son containers should each have their own responsibilities.

3. If the child container loads Service, the transaction will not take effect on that instance. That is, Spring does not automatically open a transaction when a method of service is called.

4. Based on the premise in 2: SpringMVC should only load web-related configuration (view configuration, Controller annotation scan), and Spring load data source, transaction configuration, Service and Dao annotation scan.

After reading the above, do you have any further understanding of how to solve the problem that the transaction configuration does not take effect due to the expansion of the scanning range of packages by SpringMVC? If you want to know more knowledge or related content, please follow the industry information channel, thank you for your support.

Welcome to subscribe "Shulou Technology Information " to get latest news, interesting things and hot topics in the IT industry, and controls the hottest and latest Internet news, technology news and IT industry trends.