springmvc对同名参数处理
扯淡：
中断发博客几个月，其实蛮不爽的，可能最近太忙太劳累了些，很多总结也没时间写，今天刚好遇到个小问题，就阅读下源码找找乐。因为考虑到网上大多是提供解决问题的方案，没有实际去看spring源码流程，所以就发个博文记录下，万一以后有同学搜到我的文章能深入看些东西吧。
问题描述：
前端有多个相同name的input：
<input type="text" min="1" max="31" name="xName" value="1" />
<input type="text" min="1" max="31" name="xName" value="2" />
<input type="text" min="1" max="31" name="xName" value="3" />
提交时流程原理：
一般容器在HTTP协议的Request传递到ServletContainer中后，Container就会为该次请求生成一个HTTPServletRequest对象，在HTTPServletRequest对象中，参数和值，放入到了Map中。
tomcat源码中放入map时的代码：
/**
* Put name and value pair in map. When name already exist, add value
* to array of values.
*
* @param map The map to populate
* @param name The parameter name
* @param value The parameter value
*/
private static void putMapEntry( Map map, String name, String value) {
String[] newValues = null;
String[] oldValues = (String[]) map.get(name);
if (oldValues == null) {
newValues = new String[1];
newValues[0] = value;
} else {
newValues = new String[oldValues.length + 1];
System.arraycopy(oldValues, 0, newValues, 0, oldValues.length);
newValues[oldValues.length] = value;
}
map.put(name, newValues);
}
可见同名的name，都会被放入数组的value中，而在servlet中，获取value的两个方法：
request.getParameter
request.getParameterValues
第一个获取的是数组的第一个值，第二个则获得整个数组。
springmvc框架在遇到这种同名参数提交，而参数中有逗号时，会出现问题：
比如我提交的值是 xname=123 和 xname=45,67
那么在进入action拿到参数时会变成string[] xname = ["123","45","67"]
就会影响业务逻辑正确执行。
解决方案：
就是在提交后台前，将参数进行转码，后台再进行解码就可以了。至于采用哪一种转码解码方式，其实没有什么要求，只需要注意采用方案会将逗号转码即可，知道这个关键点就好了。
实践方案：
前端代码：
$("input[name='ssidName']").each(function(){
$(this).val(encodeURIComponent($(this).val()));
})
后端java代码：
URLDecoder.decode(ssidNames [i], "UTF-8" )
灵活点的想法是：采用可逆转的转码解码也可，比如base64。有兴趣的可以尝试。
源码阅读：
虽然知道spring有这个自动组装的功能，那么我就找到这段代码：
关于springmvc原理分析这文章不错：http://www.cnblogs.com/heavenyes/p/3905844.html
我就在它后面再更进一步分析同名参数是如何处理的。
完成request中的参数和方法参数上数据的绑定：
private Object[] resolveHandlerArguments(Method handlerMethod, Object handler,
NativeWebRequest webRequest, ExtendedModelMap implicitModel) throws Exception {
// 1.获取方法参数类型的数组
Class[] paramTypes = handlerMethod.getParameterTypes();
// 声明数组,存参数的值
Object[] args = new Object[paramTypes.length];
//2.遍历参数数组,获取每个参数的值
for (int i = 0; i < args.length; i++) {
MethodParameter methodParam = new MethodParameter(handlerMethod, i);
methodParam.initParameterNameDiscovery(this.parameterNameDiscoverer);
GenericTypeResolver.resolveParameterType(methodParam, handler.getClass());
String paramName = null;
String headerName = null;
boolean requestBodyFound = false;
String cookieName = null;
String pathVarName = null;
String attrName = null;
boolean required = false;
String defaultValue = null;
boolean validate = false;
int annotationsFound = 0;
Annotation[] paramAnns = methodParam.getParameterAnnotations();
// 处理参数上的注解
for (Annotation paramAnn : paramAnns) {
if (RequestParam.class.isInstance(paramAnn)) {
RequestParam requestParam = (RequestParam) paramAnn;
paramName = requestParam.value();
required = requestParam.required();
defaultValue = parseDefaultValueAttribute(requestParam.defaultValue());
annotationsFound++;
}
else if (RequestHeader.class.isInstance(paramAnn)) {
RequestHeader requestHeader = (RequestHeader) paramAnn;
headerName = requestHeader.value();
required = requestHeader.required();
defaultValue = parseDefaultValueAttribute(requestHeader.defaultValue());
annotationsFound++;
}
else if (RequestBody.class.isInstance(paramAnn)) {
requestBodyFound = true;
annotationsFound++;
}
else if (CookieValue.class.isInstance(paramAnn)) {
CookieValue cookieValue = (CookieValue) paramAnn;
cookieName = cookieValue.value();
required = cookieValue.required();
defaultValue = parseDefaultValueAttribute(cookieValue.defaultValue());
annotationsFound++;
}
else if (PathVariable.class.isInstance(paramAnn)) {
PathVariable pathVar = (PathVariable) paramAnn;
pathVarName = pathVar.value();
annotationsFound++;
}
else if (ModelAttribute.class.isInstance(paramAnn)) {
ModelAttribute attr = (ModelAttribute) paramAnn;
attrName = attr.value();
annotationsFound++;
}
else if (Value.class.isInstance(paramAnn)) {
defaultValue = ((Value) paramAnn).value();
}
else if ("Valid".equals(paramAnn.annotationType().getSimpleName())) {
validate = true;
}
} if (annotationsFound > 1) {
throw new IllegalStateException("Handler parameter annotations are exclusive choices - " +
"do not specify more than one such annotation on the same parameter: " + handlerMethod);
} if (annotationsFound == 0) {// 如果没有注解
Object argValue = resolveCommonArgument(methodParam, webRequest);
if (argValue != WebArgumentResolver.UNRESOLVED) {
args[i] = argValue;
}
else if (defaultValue != null) {
args[i] = resolveDefaultValue(defaultValue);
}
else {
Class paramType = methodParam.getParameterType();
// 将方法声明中的Map和Model参数,放到request中,用于将数据放到request中带回页面
if (Model.class.isAssignableFrom(paramType) || Map.class.isAssignableFrom(paramType)) {
args[i] = implicitModel;
}
else if (SessionStatus.class.isAssignableFrom(paramType)) {
args[i] = this.sessionStatus;
}
else if (HttpEntity.class.isAssignableFrom(paramType)) {
args[i] = resolveHttpEntityRequest(methodParam, webRequest);
}
else if (Errors.class.isAssignableFrom(paramType)) {
throw new IllegalStateException("Errors/BindingResult argument declared " +
"without preceding model attribute. Check your handler method signature!");
}
else if (BeanUtils.isSimpleProperty(paramType)) {
paramName = "";
}
else {
attrName = "";
}
}
}
// 从request中取值,并进行赋值操作
if (paramName != null) {
// 根据paramName从request中取值,如果没有通过RequestParam注解指定paramName,则使用asm读取class文件来获取paramName
args[i] = resolveRequestParam(paramName, required, defaultValue, methodParam, webRequest, handler);
}
else if (headerName != null) {
args[i] = resolveRequestHeader(headerName, required, defaultValue, methodParam, webRequest, handler);
}
else if (requestBodyFound) {
args[i] = resolveRequestBody(methodParam, webRequest, handler);
}
else if (cookieName != null) {
args[i] = resolveCookieValue(cookieName, required, defaultValue, methodParam, webRequest, handler);
}
else if (pathVarName != null) {
args[i] = resolvePathVariable(pathVarName, methodParam, webRequest, handler);
}
else if (attrName != null) {
WebDataBinder binder =
resolveModelAttribute(attrName, methodParam, implicitModel, webRequest, handler);
boolean assignBindingResult = (args.length > i + 1 && Errors.class.isAssignableFrom(paramTypes[i + 1]));
if (binder.getTarget() != null) {
doBind(binder, webRequest, validate, !assignBindingResult);
}
args[i] = binder.getTarget();
if (assignBindingResult) {
args[i + 1] = binder.getBindingResult();
i++;
}
implicitModel.putAll(binder.getBindingResult().getModel());
}
}
// 返回参数值数组
return args;
}
resolveRequestParam方法将参数取出：
private Object resolveRequestParam (String paramName, boolean required, String defaultValue,
MethodParameter methodParam, NativeWebRequest webRequest, Object handlerForInitBinderCall)
throws Exception { Class<?> paramType = methodParam.getParameterType();
if (Map. class.isAssignableFrom(paramType) && paramName.length() == 0) {
return resolveRequestParamMap((Class<? extends Map>) paramType, webRequest);
}
if (paramName.length() == 0) {
paramName = getRequiredParameterName(methodParam);
}
Object paramValue = null;
MultipartRequest multipartRequest = webRequest.getNativeRequest(MultipartRequest.class );
if (multipartRequest != null) {
List<MultipartFile> files = multipartRequest.getFiles(paramName);
if (!files.isEmpty()) {
paramValue = (files.size() == 1 ? files.get(0) : files);
}
}
if (paramValue == null) {
//数组参数执行这行代码，相当于执行了request.getParameterValues(name)
String[] paramValues = webRequest.getParameterValues(paramName);
if (paramValues != null) {
// 取出之后，如果是同名参数则赋值整个数组 paramValue此时是object
paramValue = (paramValues. length == 1 ? paramValues[0] : paramValues);
}
}
if (paramValue == null) {
if (defaultValue != null) {
paramValue = resolveDefaultValue(defaultValue);
}
else if (required) {
raiseMissingParameterException(paramName, paramType);
}
paramValue = checkValue(paramName, paramValue, paramType);
}
WebDataBinder binder = createBinder(webRequest, null, paramName);
initBinder(handlerForInitBinderCall, paramName, binder, webRequest);
// 将paramValue根据参数类型进行一次转换操作
return binder.convertIfNecessary(paramValue, paramType, methodParam);
}
最终会执行到TypeConverterDelegate的convertIfNecessary方法：
public <T> T convertIfNecessary(String propertyName, Object oldValue, Object newValue,
Class<T> requiredType, TypeDescriptor typeDescriptor) throws IllegalArgumentException { Object convertedValue = newValue; // Custom editor for this type?
PropertyEditor editor = this. propertyEditorRegistry.findCustomEditor(requiredType, propertyName); ConversionFailedException firstAttemptEx = null; // No custom editor but custom ConversionService specified?
ConversionService conversionService = this. propertyEditorRegistry.getConversionService();
if (editor == null && conversionService != null && convertedValue != null && typeDescriptor != null) {
TypeDescriptor sourceTypeDesc = TypeDescriptor.forObject(newValue);
TypeDescriptor targetTypeDesc = typeDescriptor;
if (conversionService.canConvert(sourceTypeDesc, targetTypeDesc)) {
try {
return (T) conversionService.convert(convertedValue, sourceTypeDesc, targetTypeDesc);
}
catch (ConversionFailedException ex) {
// fallback to default conversion logic below
firstAttemptEx = ex;
}
}
} // Value not of required type?
if (editor != null || (requiredType != null && !ClassUtils.isAssignableValue(requiredType, convertedValue))) {
if (requiredType != null && Collection.class.isAssignableFrom(requiredType) && convertedValue instanceof String) {
TypeDescriptor elementType = typeDescriptor.getElementTypeDescriptor();
if (elementType != null && Enum.class.isAssignableFrom(elementType.getType())) {
convertedValue = StringUtils.commaDelimitedListToStringArray((String) convertedValue);
}
}
if (editor == null) {
editor = findDefaultEditor(requiredType);
}
convertedValue = doConvertValue(oldValue, convertedValue, requiredType, editor);
} boolean standardConversion = false; if (requiredType != null) {
// Try to apply some standard type conversion rules if appropriate. if (convertedValue != null) {
// 因为我们的type是数组，所以执行这段逻辑，他会执行StringUtils.commaDelimitedListToStringArray
if (requiredType.isArray()) {
// Array required -> apply appropriate conversion of elements.
if (convertedValue instanceof String && Enum.class.isAssignableFrom(requiredType.getComponentType())) {
convertedValue = StringUtils.commaDelimitedListToStringArray((String) convertedValue);
}
return (T) convertToTypedArray(convertedValue, propertyName, requiredType.getComponentType());
}
else if (convertedValue instanceof Collection) {
// Convert elements to target type, if determined.
convertedValue = convertToTypedCollection(
(Collection) convertedValue, propertyName, requiredType, typeDescriptor);
standardConversion = true;
}
else if (convertedValue instanceof Map) {
// Convert keys and values to respective target type, if determined.
convertedValue = convertToTypedMap(
(Map) convertedValue, propertyName, requiredType, typeDescriptor);
standardConversion = true;
}
if (convertedValue.getClass().isArray() && Array.getLength(convertedValue) == 1) {
convertedValue = Array.get(convertedValue, 0);
standardConversion = true;
}
if (String. class.equals(requiredType) && ClassUtils.isPrimitiveOrWrapper(convertedValue.getClass())) {
// We can stringify any primitive value...
return (T) convertedValue.toString();
}
else if (convertedValue instanceof String && !requiredType.isInstance(convertedValue)) {
if (firstAttemptEx == null && !requiredType.isInterface() && !requiredType.isEnum()) {
try {
Constructor strCtor = requiredType.getConstructor(String.class );
return (T) BeanUtils.instantiateClass(strCtor, convertedValue);
}
catch (NoSuchMethodException ex) {
// proceed with field lookup
if (logger.isTraceEnabled()) {
logger.trace( "No String constructor found on type [" + requiredType.getName() + "]", ex);
}
}
catch (Exception ex) {
if (logger.isDebugEnabled()) {
logger.debug( "Construction via String failed for type [" + requiredType.getName() + "]" , ex);
}
}
}
String trimmedValue = ((String) convertedValue).trim();
if (requiredType.isEnum() && "".equals(trimmedValue)) {
// It's an empty enum identifier: reset the enum value to null.
return null;
}
convertedValue = attemptToConvertStringToEnum(requiredType, trimmedValue, convertedValue);
standardConversion = true;
}
} if (!ClassUtils. isAssignableValue(requiredType, convertedValue)) {
if (firstAttemptEx != null) {
throw firstAttemptEx;
}
// Definitely doesn't match: throw IllegalArgumentException/IllegalStateException
StringBuilder msg = new StringBuilder();
msg.append( "Cannot convert value of type [").append(ClassUtils.getDescriptiveType (newValue));
msg.append( "] to required type [").append(ClassUtils.getQualifiedName (requiredType)).append("]" );
if (propertyName != null) {
msg.append( " for property '").append(propertyName).append("'");
}
if (editor != null) {
msg.append( ": PropertyEditor [").append(editor.getClass().getName()).append(
"] returned inappropriate value of type [").append(
ClassUtils. getDescriptiveType(convertedValue)).append( "]");
throw new IllegalArgumentException(msg.toString());
}
else {
msg.append( ": no matching editors or conversion strategy found");
throw new IllegalStateException(msg.toString());
}
}
} if (firstAttemptEx != null) {
if (editor == null && !standardConversion && requiredType != null && !Object.class.equals(requiredType)) {
throw firstAttemptEx;
}
logger.debug( "Original ConversionService attempt failed - ignored since " +
"PropertyEditor based conversion eventually succeeded", firstAttemptEx);
} return (T) convertedValue;
}
StringUtils.commaDelimitedListToStringArray代码：
public static String[] commaDelimitedListToStringArray (String str) {
return delimitedListToStringArray(str, ",");
}
最终执行代码，也就是哪里把这个逗号的参数区分成两个参数的地方，众里寻他千百度啊：
public static String[] delimitedListToStringArray (String str, String delimiter, String charsToDelete) {
if (str == null) {
return new String[0];
}
if (delimiter == null) {
return new String[] {str};
}
List<String> result = new ArrayList<String>();
if ( "".equals(delimiter)) {
for ( int i = 0; i < str.length(); i++) {
result.add( deleteAny(str.substring(i, i + 1), charsToDelete));
}
}
else {
int pos = 0;
int delPos;
// 逗号分隔，组装新的list
while ((delPos = str.indexOf(delimiter, pos)) != -1) {
result.add( deleteAny(str.substring(pos, delPos), charsToDelete));
pos = delPos + delimiter.length();
}
if (str.length() > 0 && pos <= str.length()) {
// Add rest of String, but not in case of empty input.
result.add( deleteAny(str.substring(pos), charsToDelete));
}
}
return toStringArray(result);
}
让我们继续前行
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努力不一定成功，但不努力肯定不会成功。