springboot扫描自定义的servlet和filter代码详解

2024-07-13 10:12:41

字体：大中小

来源：转载

供稿：网友

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")    })@Singletonpublic 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@ComponentScanpublic 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 {};}

这里有一个value()属性，上面的注解默认为basePackage,那么在扫描的时候就只扫描当前模块下面的包，其他不扫描，如果要连同其他模块一起扫描的话，给这个属性加上值即可，如下：