依赖Spring的情况下，Java Web项目如何在启动时加载数据库中的数据？

原文：https://blog.csdn.net/u012345283/article/details/39558537

原文：https://blog.csdn.net/wandrong/article/details/44782627

我的尝试：

1、继承HttpServlet，在web.xml中配置servlet的<load-on-startup>1</load-on-startup>，项目启动时globalParaService被注入了，但是跟踪到init方法里面，globalParaService为null。（失败）

public class InitSysServlet extends HttpServlet {

    private SysGlobalParaServiceI globalParaService;
    
    @Autowired
    public void setGlobalParaService(SysGlobalParaServiceI globalParaService) {
        this.globalParaService = globalParaService;
    }

    @Override
    public void init(ServletConfig config) throws ServletException {
        super.init(config);
        
        SysGlobalPara codeRule = globalParaService.getCodeRule();
        if (null != codeRule) {
            SystemConfig.IS_SET_WIZADED = "true".equals(codeRule.getSysValue());
        } else {
            SystemConfig.IS_SET_WIZADED = false;
        }
        
    }
}

然后，我试着手动创建globalParaService，代码调整为

public class InitSysServlet extends HttpServlet {

    @Override
    public void init(ServletConfig config) throws ServletException {
        super.init(config);
        
        SysGlobalParaServiceI globalParaService = new SysGlobalParaServiceImpl();
        SysGlobalPara codeRule = globalParaService.getCodeRule();
        if (null != codeRule) {
            SystemConfig.IS_SET_WIZADED = "true".equals(codeRule.getSysValue());
        } else {
            SystemConfig.IS_SET_WIZADED = false;
        }
        
    }
}

然而，SysGlobalParaServiceImpl里面依赖的其他由Spring注入的对象为null。

搞不定了，百度到以上两篇文章，根据上面文章进行尝试都成功了。

2、直接在init方法中获取Spring的bean （成功）

首先在Spring配置文件中配置SysGlobalParaServiceImpl类对应的bean，然后在代码中获取，最终代码如下：

public class InitSysServlet extends HttpServlet {

    private SysGlobalParaServiceI globalParaService;
    
    @Override
    public void init(ServletConfig config) throws ServletException {
        super.init(config);
        
        WebApplicationContext wac = ContextLoader.getCurrentWebApplicationContext();          
        globalParaService = (SysGlobalParaServiceI) wac.getBean("gpservice");

        SysGlobalPara codeRule = globalParaService.getCodeRule();
        if (null != codeRule) {
            SystemConfig.IS_SET_WIZADED = "true".equals(codeRule.getSysValue());
        } else {
            SystemConfig.IS_SET_WIZADED = false;
        }
    }
}

以下两种则与servlet无关，而是继承spring提供的接口。

3、实现Spring的接口InitializingBean，则实现类在被Sping初始化之后，会调用其中的afterPropertiesSet方法，代码如下：

@Component
public class InitSysServlet implements InitializingBean {

    private SysGlobalParaServiceI globalParaService;
    
    @Autowired
    public void setGlobalParaService(SysGlobalParaServiceI globalParaService) {
        this.globalParaService = globalParaService;
    }

    @Override
    public void afterPropertiesSet() throws Exception {
        SysGlobalPara codeRule = globalParaService.getCodeRule();
        if (null != codeRule) {
            SystemConfig.IS_SET_WIZADED = "true".equals(codeRule.getSysValue());
        } else {
            SystemConfig.IS_SET_WIZADED = false;
        }
    }


}

4、实现Spring的接口ApplicationListener<ContextRefreshedEvent>，在所有的bean初始化之后会调用其中的方法onApplicationEvent，代码如下：

@Component
public class InitSysServlet implements ApplicationListener<ContextRefreshedEvent> {

    private SysGlobalParaServiceI globalParaService;
    
    @Autowired
    public void setGlobalParaService(SysGlobalParaServiceI globalParaService) {
        this.globalParaService = globalParaService;
    }

    @Override
    public void onApplicationEvent(ContextRefreshedEvent arg0) {
        SysGlobalPara codeRule = globalParaService.getCodeRule();
        if (null != codeRule) {
            SystemConfig.IS_SET_WIZADED = "true".equals(codeRule.getSysValue());
        } else {
            SystemConfig.IS_SET_WIZADED = false;
        }
    }

}

最后，我采用的是第4中，实现Spring的接口ApplicationListener<ContextRefreshedEvent>。