完全自定义实现SpringMVC核心组件
2022-12-07 10:07:26来源：今日头条
概述
通过Spring定义请求接口非常容器，通过几个注解就可以完成，如下：
@RestController@RequestMapping("/demos")public class DemoController { @GetMapping("/index") public Object index() { return "index" ; }}通过上面的@RestController, @RequestMapping就完成了一个简单的接口定义。
实际Spring Web底层是做了很多的工作，其核心组件有HandlerMapping,HandlerAdapter,ViewResolver等组件。
【资料图】
了解了上面的几个核心组件之后，接下来就是自定义实现上面的核心类，来完成接口的请求处理。
自定义Endpoint自定义注解，标记Controller类及请求参数：
@Target(ElementType.TYPE) @Retention(RetentionPolicy.RUNTIME) @Documented public @interface PackEndpoint { }参数标记，用来对接口参数进行注解。
@Target(ElementType.PARAMETER) @Retention(RetentionPolicy.RUNTIME) @Documented public @interface PackParam { }Endpoint接口参数封装对象该对象用来保存记录，方法参数由@PackParam注解的参数。
public class PackMethodParameter { // 用来解析接口参数的名称 private ParameterNameDiscoverer parameterNameDiscoverer = new LocalVariableTableParameterNameDiscoverer() ; private String name ; private Executable executable ; private int parameterIndex ; private Class type ; public PackMethodParameter(String name, int parameterIndex, Executable executable) { this.name = name; this.parameterIndex = parameterIndex ; this.executable = executable ; } public PackMethodParameter(int parameterIndex, Executable executable, Class type) { this.parameterIndex = parameterIndex ; this.executable = executable ; this.type = type ; } public boolean hasParameterAnnotation(Class clazz) { Method method = (Method) this.executable ; Parameter[] parameters = method.getParameters() ; return parameters[this.parameterIndex].isAnnotationPresent(clazz) ; } public String getParameterName() { String[] parameterNames = parameterNameDiscoverer.getParameterNames((Method) this.executable) ; return parameterNames[this.parameterIndex] ; } }自定义HandlerMapping自定义实现了SpringMVC标准的HandlerMapping，这样在DispatcherServlet中才能够识别。
public class PackHandlerMapping implements HandlerMapping, InitializingBean, ApplicationContextAware { private ApplicationContext context; private Map mapping = new HashMap<>(); @Override public HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception { String requestPath = request.getRequestURI(); Optional opt = mapping.entrySet().stream().filter(entry -> entry.getKey().equals(requestPath)).findFirst() .map(Map.Entry::getValue); if (opt.isPresent()) { HandlerExecutionChain executionChain = new HandlerExecutionChain(opt.get()) ; return executionChain ; } return null; } // Bean初始化时，从容器中查找所有符合条件的Bean对象，即Bean对象上有@PackEndpoint注解 @Override public void afterPropertiesSet() throws Exception { String[] beanNames = context.getBeanNamesForType(Object.class) ; for (String beanName : beanNames) { Object bean = this.context.getBean(beanName) ; Class clazz = bean.getClass() ; // 判断当前的Bean上是否有PackEndpoint注解，只对有该注解的类进行处理 if (clazz.getAnnotation(PackEndpoint.class) != null) { RequestMapping clazzMapping = clazz.getAnnotation(RequestMapping.class) ; String rootPath = clazzMapping.value()[0] ; if (clazzMapping != null) { ReflectionUtils.doWithMethods(clazz, method -> { RequestMapping nestMapping = AnnotatedElementUtils.findMergedAnnotation(method, RequestMapping.class) ; if (nestMapping != null) { String nestPath = nestMapping.value()[0] ; String path = rootPath + nestPath ; PackMethodHandler handler = new PackMethodHandler(method, bean) ; mapping.put(path, handler) ; } }) ; } } } } @Override public void setApplicationContext(ApplicationContext applicationContext) throws BeansException { this.context = applicationContext; } // 该类的作用：用来记录接口对应的信息，方法，对应的实例，参数信息 public static class PackMethodHandler { private Method method; private Object instance; private PackMethodParameter[] parameters ; public Method getMethod(){ return method; } public void setMethod(Method method){ this.method = method; } public Object getInstance(){ return instance; } public void setInstance(Object instance){ this.instance = instance; } public PackMethodHandler(Method method, Object instance){ super(); this.method = method; this.instance = instance; Parameter[] params = method.getParameters() ; this.parameters = new PackMethodParameter[params.length] ; for (int i = 0; i < params.length; i++) { this.parameters[i] = new PackMethodParameter(i, method, params[i].getType()) ; } } public PackMethodParameter[] getParameter() { return this.parameters ; } }} 自定义参数解析器专门用来解析处理接口方法中的参数信息然后从请求中读取。
public interface PackHandlerMethodArgumentResolver { boolean supportsParameter(PackMethodParameter methodParameter); Object resolveArgument(PackMethodParameter methodParameter, HttpServletRequest request);}public class PackParamHandlerMethodArgumentResolver implements PackHandlerMethodArgumentResolver { @Override public boolean supportsParameter(PackMethodParameter methodParameter){ return methodParameter.hasParameterAnnotation(PackParam.class) ; } @Override public Object resolveArgument(PackMethodParameter methodParameter, HttpServletRequest request){ String name = methodParameter.getParameterName() ; Object arg = null; String[] parameterValues = request.getParameterValues(name) ; if (parameterValues != null) { arg = parameterValues.length == 1 ? parameterValues[0] : parameterValues ; } return arg ; }}自定义HandlerAdapter自定义实现了SpringMVC标准的HandlerAdatper，这样在DispatcherServlet中才能够识别。
public class PackHandlerAdapter implements HandlerAdapter{ @Resource private ConversionService conversionService ; private PackParamHandlerMethodArgumentResolver argumentResolver = new PackParamHandlerMethodArgumentResolver() ; @Override public boolean supports(Object handler){ return handler instanceof PackMethodHandler; } @Override public ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception { PackMethodHandler methodHandler = (PackMethodHandler) handler ; PackMethodParameter[] parameters = methodHandler.getParameter() ; Object[] args = new Object[parameters.length] ; for (int i = 0; i < args.length; i++) { if (this.argumentResolver.supportsParameter(parameters[i])) { // 解析对应的方法参数 args[i] = this.argumentResolver.resolveArgument(parameters[i], request) ; // 类型转换 args[i] = this.conversionService.convert(args[i], parameters[i].getType()) ; } } // 调用目标方法 Object result = methodHandler.getMethod().invoke(methodHandler.getInstance(), args) ; // 设置响应header，输出内容 response.setHeader("Content-Type", "text/plain;charset=utf8") ; PrintWriter out = response.getWriter() ; out.write((String) result) ; out.flush() ; out.close() ; return null ; } @Override public long getLastModified(HttpServletRequest request, Object handler){ return -1 ; }}通过以上的步骤就完成了一个完全自定义SpringMVC核心组件的实现。
