spring 3++的javaConfig技术_spring 3 config-优快云博客

本文链接：https://blog.youkuaiyun.com/u010435615/article/details/81370032

本文介绍如何使用JavaConfig技术替代传统的XML配置方式，包括web.xml、spring-bean的XML配置等。详细展示了如何通过注解和硬编码的方式进行配置，以及如何实现自定义的WebApplicationInitializer接口来替代web.xml配置。

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spring 3以及servlet 3以后的版本都支持javaConfig技术以及注解技术，可以抛弃web.xml以及spring的xml配置了。
不用学习xml配置的知识，直接通过注解和硬编码方式去理解，对于开发人员来说是极好的。

替代web.xml

通过实现WebApplicationInitializer接口就可以了

public class MyWebAppInitializer implements WebApplicationInitializer {

     @Override
     public void onStartup(ServletContext container) {
       XmlWebApplicationContext appContext = new XmlWebApplicationContext();
       appContext.setConfigLocation("/WEB-INF/spring/spring-mvc.xml");

       ServletRegistration.Dynamic dispatcher =
         container.addServlet("dispatcher", new DispatcherServlet(appContext));
       dispatcher.setLoadOnStartup(1);
       dispatcher.addMapping("/");
     }

  }

上面相当于如下：

<servlet>
    <servlet-name>dispatcher</servlet-name>
    <servlet-class>
      org.springframework.web.servlet.DispatcherServlet
    </servlet-class>
    <init-param>
      <param-name>contextConfigLocation</param-name>
      <param-value>/WEB-INF/spring/spring-mvc.xml</param-value>
    </init-param>
    <load-on-startup>1</load-on-startup>
  </servlet>

  <servlet-mapping>
    <servlet-name>dispatcher</servlet-name>
    <url-pattern>/</url-pattern>
  </servlet-mapping>

就是一个springmvc的实现，但spring bean还是配置在xml文件中。
先直观理解web.xml写法与javaConfig区别：
javaConfig的代码实现先创建好需要加载的配置对象，然后再创建mvc关键的DispatcherServlet对象，把DispatcherServlet需要的配置构造函数传参进去，再把DispatcherServlet对象添加到servlet的上下文中完成注册，使用注册的对象完成其他配置，例如映射的uri等。

替代xml

使用AnnotationConfigWebApplicationContext以及@Configuration、@Bean等注解方式自定义AppConfig、DispatcherConfig等的spring bean。

@Configuration
public class AppConfig {

    @Bean(name="helloBean")
    public HelloWorld helloWorld() {
        return new HelloWorldImpl();
    }

}
@Configuration
@EnableWebMvc
@ComponentScan(basePackages = "com.xxx.springmvc")
public class DispatcherConfig{
    @Bean
    public ViewResolver viewResolver() {
        InternalResourceViewResolver viewResolver = new InternalResourceViewResolver();
        viewResolver.setViewClass(JstlView.class);
        viewResolver.setPrefix("/WEB-INF/views/");
        viewResolver.setSuffix(".jsp");
        return viewResolver;
    }

} 
 public class MyWebAppInitializer implements WebApplicationInitializer {

     @Override
     public void onStartup(ServletContext container) {
       // Create the 'root' Spring application context
       AnnotationConfigWebApplicationContext rootContext =
         new AnnotationConfigWebApplicationContext();
       rootContext.register(AppConfig.class);

       // Manage the lifecycle of the root application context
       container.addListener(new ContextLoaderListener(rootContext));

       // Create the dispatcher servlet's Spring application context
       AnnotationConfigWebApplicationContext dispatcherContext =
         new AnnotationConfigWebApplicationContext();
       dispatcherContext.register(DispatcherConfig.class);

       // Register and map the dispatcher servlet
       ServletRegistration.Dynamic dispatcher =
         container.addServlet("dispatcher", new DispatcherServlet(dispatcherContext));
       dispatcher.setLoadOnStartup(1);
       dispatcher.addMapping("/");
     }

  }

没有spring的servlet实现

有些时候不需要经过spring框架去实现servlet

public class MyServlet extends HttpServlet {
    private static final long serialVersionUID = 577211309543842236L;
    public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        PrintWriter out = response.getWriter();
        out.print("doGet");
        /**
         * todo
         */
        out.close();
        out = null;
    }
    public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        request.setCharacterEncoding("UTF-8");
        response.setCharacterEncoding("UTF-8");
        PrintWriter out = response.getWriter();
        out.print("doPost");
        /**
         * todo
         */
        out.close();
        out = null;
     }
 }
  public class MyWebAppInitializer implements WebApplicationInitializer {

     @Override
     public void onStartup(ServletContext container) {

        ServletRegistration.Dynamic myServlet=
                servletContext.addServlet("myServlet", new MyServlet());
        myServlet.addMapping("/myServlet");
     }

  }

filter以及listener的javaConfig

public class TestFilter implements Filter {

    private static final Set<String> ALLOWED_PATHS = Collections.unmodifiableSet(new HashSet<>(
            Arrays.asList( "/login", "/logout", "/register")));

    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        System.out.println("init-----------filter");
    }

    @Override
    public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) throws IOException, ServletException {
        HttpServletRequest request = (HttpServletRequest) req;
        HttpServletResponse response = (HttpServletResponse) res;
        String path = request.getRequestURI().substring(request.getContextPath().length()).replaceAll("[/]+$", "");
        boolean allowedPath = ALLOWED_PATHS.contains(path);

        if (allowedPath) {
            System.out.println("这里是不需要处理的url进入的方法");
            chain.doFilter(req, res);
        } else {
            System.out.println("这里是需要处理的url进入的方法");
            System.out.println(((HttpServletRequest) req).getRequestURI());
            //chain.doFilter(req, res);
        }
    }

    @Override
    public void destroy() {
        System.out.println("destroy----------filter");
    }
}
public class MyListener implements ServletContextListener {
    @Override
    public final void contextInitialized(ServletContextEvent sce) {
        //执行初始化操作
    }
     @Override
    public void contextDestroyed(ServletContextEvent servletContextEvent) {
        //执行销毁操作
    }
}
  public class MyWebAppInitializer implements WebApplicationInitializer {

     @Override
     public void onStartup(ServletContext container) {
        /**编码过滤器*/
        FilterRegistration.Dynamic characterEncodingFilter = container
        .addFilter("encodingFilter", new CharacterEncodingFilter());
        characterEncodingFilter.setInitParameter("encoding", "UTF-8");
        characterEncodingFilter.setInitParameter("forceEncoding", "true");
        characterEncodingFilter.addMappingForUrlPatterns(null, false, "/*");
        /**自定义过滤器*/
        FilterRegistration.Dynamic testFilter = container
        .addFilter("testFilter", new TestFilter());
        testFilter.addMappingForUrlPatterns(null, false, "/*");
        /**监听器*/    
        container.addListener(ConfigListener.class);
     }

  }

servlet、filter、listener需要使用springbean

上面的情况都是没有使用springbean的，当需要的时候，直接注解注入会有问题。
需要实现两个WebApplicationInitializer，并先启动springbean配置的WebApplicationInitializer，
再自动自定义相关的WebApplicationInitializer，即可实现。

/**首先启动*/
@Order(1)
public class SpringInitializer extends
        AbstractAnnotationConfigDispatcherServletInitializer {

    @Override
    protected Class<?>[] getRootConfigClasses() {
        return new Class[] { WebMvcConfiguration.class, SpringConfiguration.class};
    }

    @Override
    protected Class<?>[] getServletConfigClasses() {
        return null;
    }

    @Override
    protected String[] getServletMappings() {
        return new String[] { "/" };
    }

}
@Order(2)
public class MyWebAppInitializer implements WebApplicationInitializer {

    @Override
    public void onStartup(ServletContext container) {

       ServletRegistration.Dynamic myServlet=
                servletContext.addServlet("myServlet", new MyServlet());
       myServlet.addMapping("/myServlet");
    }

 }
 public class MyServlet extends HttpServlet {

    private static final long serialVersionUID = -4081955072339096256L;
    @Autowired
    ISystemService systemService;

    @Override
    public void init() throws ServletException {
        super.init();
        WebApplicationContextUtils
                .getWebApplicationContext(getServletContext())
                .getAutowireCapableBeanFactory().autowireBean(this);
    }



    @Override
    public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.print(systemService.select(null));
    }

    @Override
    public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

    }

}