springboot扫描自定义的servlet和filter代码详解

这几天使用spring boot编写公司一个应用，在编写了一个filter，用于指定编码的filter，如下：

									/**

									 * Created by xiaxuan on 16/11/1.

									 */

									@WebFilter(urlPatterns = "/*",filterName="CharacterEncodeFilter",

									    initParams={

									        @WebInitParam(name="encoding",value="UTF-8"),

									        @WebInitParam(name = "forceEncoding", value = "true")

									    })

									@Singleton

									public class CharacterEncodingFilter implements Filter {

									  private String encoding = "UTF-8";

									  private boolean forceEncoding = true;

									  @Override

									  public void init(FilterConfig filterConfig) throws ServletException {

									    this.encoding = filterConfig.getInitParameter("encoding");

									    String force = filterConfig.getInitParameter("forceEncoding");

									    this.forceEncoding = (force == null) || Boolean.valueOf(force);

									  }

									  @Override

									  public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {

									    if (this.forceEncoding || request.getCharacterEncoding() == null) {

									      request.setCharacterEncoding(this.encoding);

									      response.setCharacterEncoding(this.encoding);

									    }

									    chain.doFilter(request, response);

									  }

									  @Override

									  public void destroy() {

									  }

									  public void setEncoding(String encoding) {

									    this.encoding = encoding;

									  }

									  public void setForceEncoding(boolean forceEncoding) {

									    this.forceEncoding = forceEncoding;

									  }

									}

但是在实际使用的时候，却是完全没有起作用，后来查看了一下springboot的官方文档，filter和servlet、listener之类的需要单独进行注册才能使用，但是spring boot里面提供了一个注解来替代，为@ServletComponentScan，这个注解直接加在对应的Application启动类上即可，如下：

									@SpringBootApplication

									@ServletComponentScan

									@ComponentScan

									public class SpringBootWebApplication {

									  public static void main(String[] args) {

									    SpringApplication.run(SpringBootWebApplication.class, args);

									  }

									}

这样编写完之后，如果对应的filter是在自己当前模块下的某个package中的时候是可以起作用的，但是如果本身项目中有多个模块的时候，如果filter在一个类似与core下的package中，这样注解加上去并没有多大用处，最后会发现这个filter仍然没有起作用。

我自己编写的应用有两个，最开始的做法是把filter从core包中拆出来，然后在两个模块中各自添加一个，但是这样未免有些代码冗余，并且实现方式并不优雅，然后我查看了下@ServletComponentScan的源码，里面确实是有更好的解决方法。

@ServletComponentScan的源码如下：

									/**

									 * Enables scanning for Servlet components ({@link WebFilter filters}, {@link WebServlet

									 * servlets}, and {@link WebListener listeners}). Scanning is only performed when using an

									 * embedded Servlet container.

									 * <p>

									 * Typically, one of {@code value}, {@code basePackages}, or {@code basePackageClasses}

									 * should be specified to control the packages to be scanned for components. In their

									 * absence, scanning will be performed from the package of the class with the annotation.

									 *

									 * @author Andy Wilkinson

									 * @since 1.3.0

									 * @see WebServlet

									 * @see WebFilter

									 * @see WebListener

									 */

									@Target(ElementType.TYPE)

									@Retention(RetentionPolicy.RUNTIME)

									@Documented

									@Import(ServletComponentScanRegistrar.class)

									public @interface ServletComponentScan {

									  /**

									   * Alias for the {@link #basePackages()} attribute. Allows for more concise annotation

									   * declarations e.g.: {@code @ServletComponentScan("org.my.pkg")} instead of

									   * {@code @ServletComponentScan(basePackages="org.my.pkg")}.

									   * @return the base packages to scan

									   */

									  @AliasFor("basePackages")

									  String[] value() default {};

									  /**

									   * Base packages to scan for annotated servlet components. {@link #value()} is an

									   * alias for (and mutually exclusive with) this attribute.

									   * <p>

									   * Use {@link #basePackageClasses()} for a type-safe alternative to String-based

									   * package names.

									   * @return the base packages to scan

									   */

									  @AliasFor("value")

									  String[] basePackages() default {};

									  /**

									   * Type-safe alternative to {@link #basePackages()} for specifying the packages to

									   * scan for annotated servlet components. The package of each class specified will be

									   * scanned.

									   * @return classes from the base packages to scan

									   */

									  Class<?>[] basePackageClasses() default {};

									}