[Java Spring MVC] I want to use DI in my own class

2018-11-05 Addendum

• The DI solution (method of retrieving beans via WebApplicationContext) described below will result in an error that there is no context when executed in batch or Junit test, so discuss with the staff and do not use it in this project Arranged for.
• If DI resolution is required in the self-made object, the object of the self-made class is instantiated in the class where @Inject (@Autowired) such as Controller and Service can be used.
• If you want to give the function of this self-made object to the data holding object such as Dto, set the object instantiated via DI to Dto object etc. or set the value of the processing result itself.
• Do not create a self-made class object that requires DI resolution in a class such as the Dto class where new is simply used instead of via @Inject (@Autowired) when instantiating. We will be in a position to receive injections from classes that can solve DI such as Controller.

In PHP's Laravel, getting an object globally via DI resolution from any class didn't cause any problems (which didn't happen to my knowledge), but in Spring it involves an annoying element of context, so Laravel It seems that it is not possible to have a DI solution with Hoi Hoi with a glue like this.

As usual, this is a story in a state where Spring Boot is not used, so it may not be the case when Spring Boot is introduced, but at this stage we have not been able to investigate that much.

Assigned to a Web system project using Java's Spring MVC. Spring Boot is not used because it seems to be a system made a little while ago. I'm still new to Java web systems, so it's very difficult to do.

Spring MVC seems to use annotations like "@Inject" for DI. Recently, I learned a little about domain-driven development, so I tried to make a simple domain object related to the repair part by thinking about making a domain object (an object that bears an easy-to-understand unit of work).

However, I learned that DI using annotations cannot be used in a class that does not follow the rules of Spring MVC, that is, in a self-made class. As a result of searching for an alternative method, I found it as it is, so I will briefly summarize it here.

Overview

• I want to be able to call DI resolutions in the same context as DIs that are resolved using annotations from anywhere.

import javax.servlet.ServletContext;
import javax.servlet.http.HttpServletRequest;

import org.springframework.web.context.WebApplicationContext;
import org.springframework.web.context.request.RequestAttributes;
import org.springframework.web.context.request.RequestContextHolder;
import org.springframework.web.context.request.ServletRequestAttributes;
import org.springframework.web.context.support.WebApplicationContextUtils;


(Omission)

    RequestAttributes requestAttributes = RequestContextHolder.getRequestAttributes();
    ServletRequestAttributes servletRequestAttributes = (ServletRequestAttributes) requestAttributes;
    HttpServletRequest httpServletRequest = servletRequestAttributes.getRequest();
    ServletContext servletContext = httpServletRequest.getServletContext();
    WebApplicationContext webApplicationContext =
        WebApplicationContextUtils.getRequiredWebApplicationContext(servletContext);

    //Get instance by bean definition name
    //Since it returns as Object type, cast it to the desired class
Target type variable name= (Cast to the desired mold) webApplicationContext.getBean("Bean definition name");

    //Get bean definition name list getBean()You can check the character string that can be used as an argument of.
    String[] beanDefinitionNames = webApplicationContext.getBeanDefinitionNames();

ApplicationContext.getBean ("Bean definition name")

• Instance acquisition with DI resolution without annotations.
• Since it is returned as Object type, cast it to the target class (interface) on the receiving side.
• ApplicationContext instance is WebApplicationContextUtils.getRequiredWebApplicationContext (ServletContext instance), and "WebApplicationContext" can be obtained.
• So how to get the ServletContext

Get ServletContext

• ServletContext can be obtained from the HttpServletRequest instance with getServletContext ().
• The HttpServletRequest instance is available at ((ServletRequestAttributes) RequestContextHolder.getRequestAttributes ()). getRequest ().

How to find out the bean definition name

• ʻThe Bean definition name that can be used as an argument of ApplicationContext.getBean () can be obtained by WebApplicationContext.getBeanDefinitionNames () `.
• Check by standard output or log output.

Sample class

• I made a class for DI resolution for my own class.
• I haven't learned about Spring Boot, so if I get on Boot, this kind of device may not be necessary.

package Specify the package name;

import java.util.Arrays;
import java.util.List;

import javax.servlet.ServletContext;
import javax.servlet.http.HttpServletRequest;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import org.springframework.web.context.WebApplicationContext;
import org.springframework.web.context.request.RequestAttributes;
import org.springframework.web.context.request.RequestContextHolder;
import org.springframework.web.context.request.ServletRequestAttributes;
import org.springframework.web.context.support.WebApplicationContextUtils;

/**
 *Domain object
 *DI (DependencyInjectionSolver) solver
 *In a self-made class not managed by Spring@DI using annotations such as Inject does not work, so
 *Get the DI resolved instance via this class.
 *
 *When testing the process that uses this class, JUnit's Test class says "@Annotate "WebAppConfiguration".
 */
public class DependencyInjectionSolver {
  private static final Logger logger = LoggerFactory.getLogger(DependencyInjectionSolver.class);

  /**
   *ApplicationContext for getting beans through this instance
   */
  private WebApplicationContext webApplicationContext;

  public DependencyInjectionSolver() {
    RequestAttributes requestAttributes = RequestContextHolder.getRequestAttributes();
    ServletRequestAttributes servletRequestAttributes = (ServletRequestAttributes) requestAttributes;
    HttpServletRequest httpServletRequest = servletRequestAttributes.getRequest();
    ServletContext servletContext = httpServletRequest.getServletContext();
    this.webApplicationContext = WebApplicationContextUtils.getRequiredWebApplicationContext(servletContext);
  }

  /**
   *Receive the bean definition name and get the DI resolved instance.
   *Since it returns as Object type, cast it on the acquisition side.
   *
   * @param string Bean definition name
   * @return Object
   */
  public Object getBeanByBeanName(String beanName) {
    return this.webApplicationContext.getBean(beanName);
  }

  /**
   *Get a list of defined Bean definition names.
   *GetBeanByBeanName for the names in this list()It can be used as an argument of.
   *
   * @return List<string>List of bean definition names
   */
  public List<String> gettableBeanNames() {
    String[] beanDefinitionNames = this.webApplicationContext.getBeanDefinitionNames();
    return Arrays.asList(beanDefinitionNames);
  }
}

User side

DependencyInjectionSolver diSolver = new DependencyInjectionSolver();
Variable name such as interface name= (Interface name etc.) diSolver.getBeanByBeanName("Bean definition name");