原生SpringMVC有如下缺陷
- 参数的JSON反序列化只支持
@RequestBody注解，这意味着不能在controller方法中写多个参数，如下代码是不对的public Map test(@RequestBody User user, @RequestBody Role role) - 如下代码，User和Role类都有id字段。假如请求方式是默认的x-www-form-urlencoded格式，那么请求test方法的http请求实体将类似于
id=1234&userName=uuuu&roleName=rrrrr，但实际上我们希望传两个id且代表不同的意思。另外，如果User中有School类的成员，School类中有schoolName字段，那么请求参数仅会变成id=1234&userName=uuuu&roleName=rrrrr&&schoolName=ssss。可见这种参数绑定方式有歧义而且没有属性的层级概念public class User { private int id; private String userName; ... } public class Role { private int id; private String roleName; ... } // controller的方法 public Map test(User user, Role role) - JSON参数绑定不能支持Map参数。如下代码中的userMap将会被SpringMVC初始化成
BindingAwareModelMap，而不是前端传过来的JSON对象public Map test(@RequestParam Map<String, User> userMap) - 参数校验不支持原始类型、原始类型的包装类。如下代码的校验不会起作用，原因是SpringMVC是对方法参数遍历，分别对每一个参数用适配的参数解析器把request中的parameter转换成参数，在参数解析器中只能知道当前的参数类型和HttpRequest，无法得到test方法的第N个参数带有什么注解
public Map test(@Valid @Range(min=1, max=10) Integer limit)
对上述缺陷的想法
- 可以用增加一个参数解析器去解析
@JsonParam注解,请求格式第一层是x-www-form-urlencode，第二层是JSON格式，如下例子（未进行encode）使得请求参数不具有歧义、且有属性有层次user={"id": 123, "userName": "abc"}&role={"id": 456, "roleName": "admin"} - SpringMVC默认使用
RequestMappingHandlerAdapter去初始化24个参数解析器，把我们拓展的自定义参数解析器排在后面，并且不允许修改顺序。这就导致了MapMethodProcessor比我们的解析器先处理Map参数，返回了ModelMap。因此不能通过增加参数解析器去处理无法传入Map参数的问题。 - Spring在初始化一个bean后，在放入BeanFactory前，首先会让
BeanPostProcessor对bean进行后处理，同时RequestMappingHandlerAdapter可以通过setArgumentResolvers方法覆盖默认的参数解析器，因此我们可以新建一个后置Bean处理器去处理RequestMappingHandlerAdapter，首先通过getArgumentResolvers拿到参数解析器列表，然后在列表的最前面加上我们自定义的参数解析器，使得我们的参数解析器比MapMethodProcessor要先处理，这样就能解析转换Map参数 JSR-303规范中定义了两个接口，一个是javax.validation.Validator，一个是javax.validation.executable.ExecutableValidator，其中Validator能对一个实体bean进行校验，ExecutableValidator能够对一个方法中的所有带有@Valid注解的参数进行校验，SpringMVC的参数解析器使用的是Validator。为了解决缺陷4，可以使用切面对Controller的方法进行处理，在调用方法之前，先用ExecutableValidator对方法参数进行处理。注意：如果使用Tomcat容器环境，则需要把切面定义在SpringMVC的配置文件中，而不是配置Spring的配置文件中，它们的上下文是不同的，Spring读不到SpringMVC的bean。Spring boot没有这个问题。
实现代码
json参数注解：
package com.baidu.waimai.springext;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
@Target({ ElementType.PARAMETER })
@Retention(RetentionPolicy.RUNTIME)
public @interface JsonParam {
String value();
boolean required() default true;
String defaultValue() default "";
}
@JsonParam的参数解析器，参考自org.springframework.web.method.annotation.ModelAttributeMethodProcessor，使用FastJson来做参数转换，做了实体bean的参数校验：
package com.baidu.waimai.springext;
import com.alibaba.fastjson.JSON;
import com.alibaba.fastjson.parser.Feature;
import org.springframework.core.MethodParameter;
import org.springframework.core.annotation.AnnotationUtils;
import org.springframework.validation.BindException;
import org.springframework.validation.Errors;
import org.springframework.validation.annotation.Validated;
import org.springframework.web.bind.ServletRequestDataBinder;
import org.springframework.web.bind.WebDataBinder;
import org.springframework.web.bind.support.WebDataBinderFactory;
import org.springframework.web.context.request.NativeWebRequest;
import org.springframework.web.method.support.HandlerMethodArgumentResolver;
import org.springframework.web.method.support.ModelAndViewContainer;
import javax.servlet.ServletRequest;
import java.lang.annotation.Annotation;
import java.util.Map;
public class JsonArgumentResolver implements HandlerMethodArgumentResolver {
@Override
public boolean supportsParameter(MethodParameter parameter) {
JsonParam jsonParam = parameter.getParameterAnnotation(JsonParam.class);
return jsonParam != null;
}
protected Object resolveName(String name, MethodParameter methodParameter, NativeWebRequest nativeWebRequest)
throws Exception {
String[] paramValues1 = nativeWebRequest.getParameterValues(name);
if (paramValues1 != null) {
return paramValues1.length == 1
? JSON.parseObject(
paramValues1[0], methodParameter.getNestedGenericParameterType(), Feature.OrderedField)
: paramValues1;
}
return null;
}
@Override
public Object resolveArgument(MethodParameter parameter, ModelAndViewContainer mavContainer,
NativeWebRequest webRequest, WebDataBinderFactory binderFactory) throws Exception {
JsonParam jsonParam = parameter.getParameterAnnotation(JsonParam.class);
Object target = resolveName(jsonParam.value(), parameter, webRequest);
WebDataBinder binder = binderFactory.createBinder(webRequest, target, jsonParam.value());
if (binder.getTarget() != null) {
bindRequestParameters(binder, webRequest);
validateIfApplicable(binder, parameter);
if (binder.getBindingResult().hasErrors() && isBindExceptionRequired(binder, parameter)) {
throw new BindException(binder.getBindingResult());
}
}
// Add resolved attribute and BindingResult at the end of the model
Map<String, Object> bindingResultModel = binder.getBindingResult().getModel();
mavContainer.removeAttributes(bindingResultModel);
mavContainer.addAllAttributes(bindingResultModel);
return binder.convertIfNecessary(binder.getTarget(), parameter.getParameterType(), parameter);
}
protected void bindRequestParameters(WebDataBinder binder, NativeWebRequest request) {
ServletRequest servletRequest = request.getNativeRequest(ServletRequest.class);
ServletRequestDataBinder servletBinder = (ServletRequestDataBinder) binder;
servletBinder.bind(servletRequest);
}
protected void validateIfApplicable(WebDataBinder binder, MethodParameter methodParam) {
Annotation[] annotations = methodParam.getParameterAnnotations();
for (Annotation ann : annotations) {
Validated validatedAnn = AnnotationUtils.getAnnotation(ann, Validated.class);
if (validatedAnn != null || ann.annotationType().getSimpleName().startsWith("Valid")) {
Object hints = (validatedAnn != null ? validatedAnn.value() : AnnotationUtils.getValue(ann));
Object[] validationHints = (hints instanceof Object[] ? (Object[]) hints : new Object[] { hints });
binder.validate(validationHints);
break;
}
}
}
protected boolean isBindExceptionRequired(WebDataBinder binder, MethodParameter methodParam) {
int i = methodParam.getParameterIndex();
Class<?>[] paramTypes = methodParam.getMethod().getParameterTypes();
boolean hasBindingResult = (paramTypes.length > (i + 1) && Errors.class.isAssignableFrom(paramTypes[i + 1]));
return !hasBindingResult;
}
}
参数校验切面：
package com.baidu.waimai.springext;
import com.baidu.waimai.validator.ParameterBindingResult;
import org.aspectj.lang.ProceedingJoinPoint;
import org.aspectj.lang.annotation.Around;
import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.Pointcut;
import org.aspectj.lang.reflect.MethodSignature;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;
import org.springframework.validation.BindException;
import org.springframework.validation.Errors;
import org.springframework.validation.beanvalidation.SpringValidatorAdapter;
import javax.validation.ConstraintViolation;
import javax.validation.Validator;
import javax.validation.executable.ExecutableValidator;
import java.lang.reflect.Method;
import java.util.HashSet;
import java.util.Set;
@Aspect
@Component
public class ControllerParameterValidateAspect {
@Autowired
private Validator validator; // 需要注入ExtendValidator
@Pointcut("execution(public * com.baidu.waimai.controller.*.*(..))")
private void anyControllerMethod() {}//定义一个切入点
@Around("anyControllerMethod()")
public Object validateParameters(ProceedingJoinPoint joinPoint) throws Throwable {
Object[] args = joinPoint.getArgs();
// 只有MethodSignature才能获取到方法，才能获取参数列表中的注解
if (validator != null && validator instanceof ExecutableValidator &&
joinPoint.getSignature() instanceof MethodSignature) {
Method method = ((MethodSignature) joinPoint.getSignature()).getMethod();
ParameterBindingResult errors = new ParameterBindingResult(
joinPoint.getTarget(), method, args, joinPoint.getTarget().toString());
new ExtendSpringValidatorAdapter(validator)
.validateParameters(errors, joinPoint.getTarget(), method, args);
if (errors.hasErrors()) {
throw new BindException(errors);
}
}
return joinPoint.proceed(args);
}
private static class ExtendSpringValidatorAdapter extends SpringValidatorAdapter {
public ExtendSpringValidatorAdapter(Validator targetValidator) {
super(targetValidator);
}
public <T> void validateParameters(Errors errors, T obj, Method method, Object[] params, Class... classes) {
ExecutableValidator validator = (ExecutableValidator)unwrap(Validator.class);
Set<ConstraintViolation<Object>> constraintViolations =
validator.validateParameters(obj, method, params, classes);
processConstraintViolations(constraintViolations, errors);
}
}
}
拓展校验器，让LocalValidatorFactoryBean拥有ExecutableValidator的功能：
package com.baidu.waimai.springext;
import org.springframework.validation.Errors;
import org.springframework.validation.beanvalidation.LocalValidatorFactoryBean;
import javax.validation.ConstraintViolation;
import javax.validation.executable.ExecutableValidator;
import java.lang.reflect.Constructor;
import java.lang.reflect.Method;
import java.util.Collection;
import java.util.Collections;
import java.util.Set;
public class ExtendValidator extends LocalValidatorFactoryBean implements ExecutableValidator {
@Override
protected void processConstraintViolations(Set<ConstraintViolation<Object>> violations, Errors errors) {
super.processConstraintViolations(violations, errors);
}
@Override
public void validate(Object target, Errors errors, Object... validationHints) {
if (target instanceof Collection) {
validateCollectionHints(((Collection) target), errors, validationHints);
} else {
super.validate(target, errors, validationHints);
}
}
@Override
public <T> Set<ConstraintViolation<T>> validateParameters(T t, Method method, Object[] objects, Class<?>... classes) {
if (getValidator() instanceof ExecutableValidator) {
return ((ExecutableValidator) getValidator()).validateParameters(t, method, objects, classes);
}
return Collections.emptySet();
}
@Override
public <T> Set<ConstraintViolation<T>> validateReturnValue(T t, Method method, Object o, Class<?>... classes) {
if (getValidator() instanceof ExecutableValidator) {
return ((ExecutableValidator) getValidator())
.validateReturnValue(t, method, o, classes);
}
return Collections.emptySet();
}
@Override
public <T> Set<ConstraintViolation<T>> validateConstructorParameters(Constructor<? extends T> constructor, Object[] objects, Class<?>... classes) {
if (getValidator() instanceof ExecutableValidator) {
return ((ExecutableValidator) getValidator())
.validateConstructorParameters(constructor, objects, classes);
}
return Collections.emptySet();
}
@Override
public <T> Set<ConstraintViolation<T>> validateConstructorReturnValue(Constructor<? extends T> constructor, T t, Class<?>... classes) {
if (getValidator() instanceof ExecutableValidator) {
return ((ExecutableValidator) getValidator())
.validateConstructorReturnValue(constructor, t, classes);
}
return Collections.emptySet();
}
private void validateCollectionHints(Collection collection, Errors errors, Object... validationHints) {
if (collection != null) {
for (Object item : collection) {
validate(item, errors, validationHints);
}
}
}
}
增加一个参数绑定结果：
package com.baidu.waimai.springext;
import org.springframework.validation.AbstractBindingResult;
import java.lang.reflect.Method;
import java.lang.reflect.Parameter;
public class ParameterBindingResult extends AbstractBindingResult {
private Object target;
private Method method;
private Object[] args;
public ParameterBindingResult(Object target, Method method, Object[] args, String targetName) {
super(targetName);
this.target = target;
this.method = method;
this.args = args;
}
@Override
public Object getTarget() {
return target;
}
@Override
protected Object getActualFieldValue(String field) {
for (int i = 0; i < method.getParameters().length; i++) {
Parameter parameter = method.getParameters()[i];
if (parameter.getName().equals(field)) {
return args[i];
}
}
return null;
}
public Method getMethod() {
return method;
}
public Object[] getArgs() {
return args;
}
}
后置bean处理器：
package com.baidu.waimai.springext;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanPostProcessor;
import org.springframework.stereotype.Component;
import org.springframework.web.method.support.HandlerMethodArgumentResolver;
import org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter;
import java.util.LinkedList;
import java.util.List;
@Component
public class RequestMappingHandlerAdapterPostProcessor implements BeanPostProcessor {
@Override
public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
return bean;
}
@Override
public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
if (bean instanceof RequestMappingHandlerAdapter) {
RequestMappingHandlerAdapter adapter = (RequestMappingHandlerAdapter) bean;
List<HandlerMethodArgumentResolver> argumentResolvers = adapter.getArgumentResolvers();
List<HandlerMethodArgumentResolver> newArgumentResolvers =
processHandlerMethodArgumentResolvers(argumentResolvers);
if (newArgumentResolvers != null) {
adapter.setArgumentResolvers(newArgumentResolvers);
}
}
return bean;
}
protected List<HandlerMethodArgumentResolver> processHandlerMethodArgumentResolvers(
List<HandlerMethodArgumentResolver> argumentResolvers) {
List<HandlerMethodArgumentResolver> newArgumentResolvers = new LinkedList<>(argumentResolvers);
newArgumentResolvers.add(0, new JsonArgumentResolver()); // 关键，插入在前面，使得带有@JsonParam的参数被优先处理
return newArgumentResolvers;
}
}
异常处理器：
package com.baidu.waimai.springext;
import org.springframework.core.annotation.Order;
import org.springframework.validation.BindException;
import org.springframework.validation.ObjectError;
import org.springframework.web.servlet.HandlerExceptionResolver;
import org.springframework.web.servlet.ModelAndView;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.lang.reflect.UndeclaredThrowableException;
import java.util.List;
@Order(1) // 排序要在SpringMvc默认异常处理器的前面
public class BindExceptionHandler implements HandlerExceptionResolver {
@Override
public ModelAndView resolveException(HttpServletRequest req, HttpServletResponse resp, Object o, Exception e) {
if (e instanceof BindException) {
return resolveBindException(e);
// 在Controller的方法加上切面时抛出的异常是UndeclaredThrowableException
// 需要判断里面的是不是BindException
} else if (e instanceof UndeclaredThrowableException) {
Throwable undeclaredThrowable = ((UndeclaredThrowableException) e).getUndeclaredThrowable();
if (undeclaredThrowable instanceof BindException) {
return resolveBindException(undeclaredThrowable);
}
}
return null;
}
private ModelAndView resolveBindException(Throwable e) {
BindException be = (BindException) e;
List<ObjectError> errors = be.getBindingResult().getAllErrors();
ObjectError oe = errors.get(0);
ModelAndView mav = new ModelAndView();
BindExceptionJsonView view = new BindExceptionJsonView();
mav.setView(view);
mav.addObject("Exception", e);
mav.addObject("ObjectError", oe);
return mav;
}
}
绑定异常的ModelAndView：
package com.baidu.waimai.springext;
import com.alibaba.fastjson.JSON;
import com.alibaba.fastjson.serializer.SerializerFeature;
import com.baidu.waimai.util.ResponseUtil;
import org.springframework.validation.ObjectError;
import org.springframework.web.servlet.view.AbstractView;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.PrintWriter;
import java.util.LinkedHashMap;
import java.util.Map;
public class BindExceptionJsonView extends AbstractView {
@Override
protected void renderMergedOutputModel(
Map<String, Object> context, HttpServletRequest req, HttpServletResponse resp) throws Exception {
String OBJECT_ERROR = "ObjectError";
resp.setContentType(ResponseUtil.JSON_CONTENT_TYPE);
PrintWriter out = resp.getWriter();
Map map = new LinkedHashMap();
ObjectError oe = (ObjectError) context.get(OBJECT_ERROR);
map.put(ResponseUtil.STATUS, 0);
map.put(ResponseUtil.MSG, "参数校验错误");
map.put(OBJECT_ERROR, oe);
out.print(JSON.toJSONString(map, SerializerFeature.PrettyFormat, SerializerFeature.SortField));
}
}