springMVC源码解析--HandlerMethodArgumentResolverComposite参数解析器集合（二）
springMVC源码分析--RequestParamMethodArgumentResolver参数解析器（三）
HandlerMethodArgumentResolver是用来为处理器解析参数的，主要用在HandlerMethod中，每个Resolver对应一种类型的参数，其实现类特别的多。
HandlerMethodArgumentResolver接口及其实现类如下：

HandlerMethodArgumentResolver接口及其实现类.png

HandlerMethodArgumentResolver的接口定义如下：
（1）supportsParameter 用于判断是否支持对某种参数的解析
（2）resolveArgument 将请求中的参数值解析为某种对象

public interface HandlerMethodArgumentResolver {  
  
    /**  
     * Whether the given {@linkplain MethodParameter method parameter} is  
     * supported by this resolver.  
     * @param parameter the method parameter to check  
     * @return {@code true} if this resolver supports the supplied parameter;  
     * {@code false} otherwise  
     */  
    //判断是否支持某种类型的函数参数  
    boolean supportsParameter(MethodParameter parameter);  
  
    /**  
     * Resolves a method parameter into an argument value from a given request.  
     * A {@link ModelAndViewContainer} provides access to the model for the  
     * request. A {@link WebDataBinderFactory} provides a way to create  
     * a {@link WebDataBinder} instance when needed for data binding and  
     * type conversion purposes.  
     * @param parameter the method parameter to resolve. This parameter must  
     * have previously been passed to  
     * {@link #supportsParameter(org.springframework.core.MethodParameter)}  
     * and it must have returned {@code true}  
     * @param mavContainer the ModelAndViewContainer for the current request  
     * @param webRequest the current request  
     * @param binderFactory a factory for creating {@link WebDataBinder} instances  
     * @return the resolved argument value, or {@code null}.  
     * @throws Exception in case of errors with the preparation of argument values  
     */  
    //解析请求中的参数为某个函数的参数对象  
    Object resolveArgument(MethodParameter parameter, ModelAndViewContainer mavContainer,  
            NativeWebRequest webRequest, WebDataBinderFactory binderFactory) throws Exception;  
}

HandlerMethodArgumentResolver的执行流程：
参数的处理是在InvocableHandlerMethod中，当执行具体的请求处理时执行invokeForRequest函数

public class InvocableHandlerMethod extends HandlerMethod {
    .....
    public Object invokeForRequest(NativeWebRequest request, ModelAndViewContainer mavContainer, Object... providedArgs) throws Exception {
        //获取执行Controller的函数的参数对象  
        Object[] args = this.getMethodArgumentValues(request, mavContainer, providedArgs);
        if(this.logger.isTraceEnabled()) {
            this.logger.trace("Invoking \'" + ClassUtils.getQualifiedMethodName(this.getMethod(), this.getBeanType()) + "\' with arguments " + Arrays.toString(args));
        }

        Object returnValue = this.doInvoke(args);
        if(this.logger.isTraceEnabled()) {
            this.logger.trace("Method [" + ClassUtils.getQualifiedMethodName(this.getMethod(), this.getBeanType()) + "] returned [" + returnValue + "]");
        }
        return returnValue;
    }
}

具体的参数解析器的选择和使用参数解析器去解析参数的实现都在getMethodArgumentValues中，首先springMVC在启动时会将所有的参数解析器放到HandlerMethodArgumentResolverComposite，HandlerMethodArgumentResolverComposite是所有参数的一个集合，接下来就是从HandlerMethodArgumentResolverComposite参数解析器集合中选择一个支持对parameter解析的参数解析器，接下来就使用支持参数解析的解析器进行参数解析。

private Object[] getMethodArgumentValues(NativeWebRequest request, ModelAndViewContainer mavContainer,  
            Object... providedArgs) throws Exception {  
        //获取执行的具体函数的参数  
        MethodParameter[] parameters = getMethodParameters();  
        Object[] args = new Object[parameters.length];  
        for (int i = 0; i < parameters.length; i++) {  
            MethodParameter parameter = parameters[i];  
            parameter.initParameterNameDiscovery(this.parameterNameDiscoverer);  
            GenericTypeResolver.resolveParameterType(parameter, getBean().getClass());  
            //获取参数值对象  
            args[i] = resolveProvidedArgument(parameter, providedArgs);  
            if (args[i] != null) {  
                continue;  
            }  
            //首先判断是否有参数解析器支持参数parameter，采用职责链的设计模式  
            if (this.argumentResolvers.supportsParameter(parameter)) {  
                try {  
                    //如果参数解析器支持解析参数parameter，那么解析参数成Controller的函数需要的格式  
                    args[i] = this.argumentResolvers.resolveArgument(  
                            parameter, mavContainer, request, this.dataBinderFactory);  
                    continue;  
                }  
                catch (Exception ex) {  
                    if (logger.isDebugEnabled()) {  
                        logger.debug(getArgumentResolutionErrorMessage("Error resolving argument", i), ex);  
                    }  
                    throw ex;  
                }  
            }  
            if (args[i] == null) {  
                String msg = getArgumentResolutionErrorMessage("No suitable resolver for argument", i);  
                throw new IllegalStateException(msg);  
            }  
        }  
        //返回参数值  
        return args;  
    } 

以上代码会将我们通过链接提交的参数值转换为对象值。

转载于：http://blog.csdn.net/qq924862077/article/details/54177442