spring mvc 空字符串也用默认值
方法有多种
1。可以使用过滤器/拦截器把空字符串设置成null
2. 修改spring mvc
AbstractNamedValueMethodArgumentResolver
的 源码，当然不是直接修改jar了。
这儿用的是第二种方式。
首先创建包：
org.springframework.web.method.annotation
然后再这个包下把这个类复制过来修改。
下面是修改后的的
/*
* Copyright 2002-2013 the original author or authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.springframework.web.method.annotation;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import javax.servlet.ServletException;
import org.springframework.beans.factory.config.BeanExpressionContext;
import org.springframework.beans.factory.config.BeanExpressionResolver;
import org.springframework.beans.factory.config.ConfigurableBeanFactory;
import org.springframework.core.MethodParameter;
import org.springframework.util.Assert;
import org.springframework.web.bind.WebDataBinder;
import org.springframework.web.bind.annotation.ValueConstants;
import org.springframework.web.bind.support.WebDataBinderFactory;
import org.springframework.web.context.request.NativeWebRequest;
import org.springframework.web.context.request.RequestScope;
import org.springframework.web.method.support.HandlerMethodArgumentResolver;
import org.springframework.web.method.support.ModelAndViewContainer;
/**
* Abstract base class for resolving method arguments from a named value.
* Request parameters, request headers, and path variables are examples of named
* values. Each may have a name, a required flag, and a default value.
* <p>Subclasses define how to do the following:
* <ul>
* <li>Obtain named value information for a method parameter
* <li>Resolve names into argument values
* <li>Handle missing argument values when argument values are required
* <li>Optionally handle a resolved value
* </ul>
* <p>A default value string can contain ${...} placeholders and Spring Expression
* Language #{...} expressions. For this to work a
* {@link ConfigurableBeanFactory} must be supplied to the class constructor.
* <p>A {@link WebDataBinder} is created to apply type conversion to the resolved
* argument value if it doesn't match the method parameter type.
*
* @author Arjen Poutsma
* @author Rossen Stoyanchev
* @since 3.1
*/
public abstract class AbstractNamedValueMethodArgumentResolver implements HandlerMethodArgumentResolver {
private final ConfigurableBeanFactory configurableBeanFactory;
private final BeanExpressionContext expressionContext;
private Map<MethodParameter, NamedValueInfo> namedValueInfoCache =
new ConcurrentHashMap<MethodParameter, NamedValueInfo>(256);
/**
* @param beanFactory a bean factory to use for resolving ${...} placeholder
* and #{...} SpEL expressions in default values, or {@code null} if default
* values are not expected to contain expressions
*/
public AbstractNamedValueMethodArgumentResolver(ConfigurableBeanFactory beanFactory) {
this.configurableBeanFactory = beanFactory;
this.expressionContext = (beanFactory != null) ? new BeanExpressionContext(beanFactory, new RequestScope()) : null;
}
@Override
public final Object resolveArgument(
MethodParameter parameter, ModelAndViewContainer mavContainer,
NativeWebRequest webRequest, WebDataBinderFactory binderFactory)
throws Exception {
Class<?> paramType = parameter.getParameterType();
NamedValueInfo namedValueInfo = getNamedValueInfo(parameter);
//这儿是修改部分
Object arg = resolveName(namedValueInfo.name, parameter, webRequest);
if (arg == null || "".equals(arg)) {
if (namedValueInfo.defaultValue != null) {
arg = resolveDefaultValue(namedValueInfo.defaultValue);
}
else if (namedValueInfo.required) {
handleMissingValue(namedValueInfo.name, parameter);
}
arg = handleNullValue(namedValueInfo.name, arg, paramType);
}
/*else if (namedValueInfo.defaultValue != null) {
arg = resolveDefaultValue(namedValueInfo.defaultValue);
}
*/
if (binderFactory != null) {
WebDataBinder binder = binderFactory.createBinder(webRequest, null, namedValueInfo.name);
arg = binder.convertIfNecessary(arg, paramType, parameter);
}
handleResolvedValue(arg, namedValueInfo.name, parameter, mavContainer, webRequest);
return arg;
}
/**
* Obtain the named value for the given method parameter.
*/
private NamedValueInfo getNamedValueInfo(MethodParameter parameter) {
NamedValueInfo namedValueInfo = this.namedValueInfoCache.get(parameter);
if (namedValueInfo == null) {
namedValueInfo = createNamedValueInfo(parameter);
namedValueInfo = updateNamedValueInfo(parameter, namedValueInfo);
this.namedValueInfoCache.put(parameter, namedValueInfo);
}
return namedValueInfo;
}
/**
* Create the {@link NamedValueInfo} object for the given method parameter. Implementations typically
* retrieve the method annotation by means of {@link MethodParameter#getParameterAnnotation(Class)}.
* @param parameter the method parameter
* @return the named value information
*/
protected abstract NamedValueInfo createNamedValueInfo(MethodParameter parameter);
/**
* Create a new NamedValueInfo based on the given NamedValueInfo with sanitized values.
*/
private NamedValueInfo updateNamedValueInfo(MethodParameter parameter, NamedValueInfo info) {
String name = info.name;
if (info.name.length() == 0) {
name = parameter.getParameterName();
Assert.notNull(name, "Name for argument type [" + parameter.getParameterType().getName()
+ "] not available, and parameter name information not found in class file either.");
}
String defaultValue = (ValueConstants.DEFAULT_NONE.equals(info.defaultValue) ? null : info.defaultValue);
return new NamedValueInfo(name, info.required, defaultValue);
}
/**
* Resolves the given parameter type and value name into an argument value.
* @param name the name of the value being resolved
* @param parameter the method parameter to resolve to an argument value
* @param request the current request
* @return the resolved argument. May be {@code null}
* @throws Exception in case of errors
*/
protected abstract Object resolveName(String name, MethodParameter parameter, NativeWebRequest request)
throws Exception;
/**
* Resolves the given default value into an argument value.
*/
private Object resolveDefaultValue(String defaultValue) {
if (this.configurableBeanFactory == null) {
return defaultValue;
}
String placeholdersResolved = this.configurableBeanFactory.resolveEmbeddedValue(defaultValue);
BeanExpressionResolver exprResolver = this.configurableBeanFactory.getBeanExpressionResolver();
if (exprResolver == null) {
return defaultValue;
}
return exprResolver.evaluate(placeholdersResolved, this.expressionContext);
}
/**
* Invoked when a named value is required, but {@link #resolveName(String, MethodParameter, NativeWebRequest)}
* returned {@code null} and there is no default value. Subclasses typically throw an exception in this case.
* @param name the name for the value
* @param parameter the method parameter
*/
protected abstract void handleMissingValue(String name, MethodParameter parameter) throws ServletException;
/**
* A {@code null} results in a {@code false} value for {@code boolean}s or an exception for other primitives.
*/
private Object handleNullValue(String name, Object value, Class<?> paramType) {
if (value == null) {
if (Boolean.TYPE.equals(paramType)) {
return Boolean.FALSE;
}
else if (paramType.isPrimitive()) {
throw new IllegalStateException("Optional " + paramType + " parameter '" + name +
"' is present but cannot be translated into a null value due to being declared as a " +
"primitive type. Consider declaring it as object wrapper for the corresponding primitive type.");
}
}
return value;
}
/**
* Invoked after a value is resolved.
* @param arg the resolved argument value
* @param name the argument name
* @param parameter the argument parameter type
* @param mavContainer the {@link ModelAndViewContainer}, which may be {@code null}
* @param webRequest the current request
*/
protected void handleResolvedValue(Object arg, String name, MethodParameter parameter,
ModelAndViewContainer mavContainer, NativeWebRequest webRequest) {
}
/**
* Represents the information about a named value, including name, whether it's required and a default value.
*/
protected static class NamedValueInfo {
private final String name;
private final boolean required;
private final String defaultValue;
protected NamedValueInfo(String name, boolean required, String defaultValue) {
this.name = name;
this.required = required;
this.defaultValue = defaultValue;
}
}
}