17.springmvc源码学习（十七）@MatrixVariable的使用及原理
17.springmvc源码学习（十七）@MatrixVariable的使用及原理
目录
前言
@MatrixVariable可以从url中获取路径参数。
一、使用
单个参数
接口方法：
@ApiOperation(value = "测试@MatrixVariable", notes = "单个参数")
@GetMapping(value = "/matrix/{param}", produces = {MediaType.APPLICATION_JSON_VALUE})
public ResponseEntity aaa(@PathVariable String param, @MatrixVariable String var) throws BaseException {
ResponseEntity responseEntity = new ResponseEntity();
System.out.println("param: " + param);
System.out.println("var: " + var);
return responseEntity;
}请求路径：
matrix/param1;var=matrixVar结果：
param: param1
var: matrixVar多个参数
接口方法：
@ApiOperation(value = "测试@MatrixVariable", notes = "多个参数")
@GetMapping(value = "/matrix/{param}/{param2}", produces = {MediaType.APPLICATION_JSON_VALUE})
public ResponseEntity aaa(@PathVariable String param, @MatrixVariable(pathVar = "param2") String var) throws BaseException {
ResponseEntity responseEntity = new ResponseEntity();
System.out.println("param: " + param);
System.out.println("var: " + var);
return responseEntity;
}请求路径：
matrix/param1;var=matrixVar;var1=matrixVar/param2;var=matrixVar2结果：
param: param1
var: matrixVar2Map类型参数
接口方法：
@ApiOperation(value = "测试@MatrixVariable", notes = "多个参数")
@GetMapping(value = "/matrix/{param}/{param2}", produces = {MediaType.APPLICATION_JSON_VALUE})
public ResponseEntity aaa(@PathVariable String param, @MatrixVariable(pathVar = "param1") Map var) throws BaseException {
ResponseEntity responseEntity = new ResponseEntity();
System.out.println("param: " + param);
System.out.println("var: " + var);
return responseEntity;
}请求路径：
matrix/param1;var=matrixVar;var1=matrixVar/param2;var=matrixVar2结果：
param: param1
var: {var=matrixVar1, var1=matrixVar1}二、原理
1 解析路径参数
在获取处理器的过程中，RequestMappingHandlerMapping调用getHandler方法，找到匹配当前请求的HandlerMethod，然后处理匹配到的HandlerMapping，进而解析路径的参数
（1）handleMatch( )
RequestMappingInfoHandlerMapping.java
protected void handleMatch(RequestMappingInfo info, String lookupPath, HttpServletRequest request) {
super.handleMatch(info, lookupPath, request);
RequestCondition<?> condition = info.getActivePatternsCondition();
if (condition instanceof PathPatternsRequestCondition) {
extractMatchDetails((PathPatternsRequestCondition) condition, lookupPath, request);
}
else {
//提取路径里的详细信息
extractMatchDetails((PatternsRequestCondition) condition, lookupPath, request);
}
if (!info.getProducesCondition().getProducibleMediaTypes().isEmpty()) {
Set<MediaType> mediaTypes = info.getProducesCondition().getProducibleMediaTypes();
request.setAttribute(PRODUCIBLE_MEDIA_TYPES_ATTRIBUTE, mediaTypes);
}
}（2）extractMatchDetails( )
private void extractMatchDetails(
PatternsRequestCondition condition, String lookupPath, HttpServletRequest request) {
String bestPattern;
Map<String, String> uriVariables;
if (condition.isEmptyPathMapping()) {
bestPattern = lookupPath;
uriVariables = Collections.emptyMap();
}
else {
bestPattern = condition.getPatterns().iterator().next();
//提取出UriTemplateVariables参数值，供@PathVariable使用
uriVariables = getPathMatcher().extractUriTemplateVariables(bestPattern, lookupPath);
if (!getUrlPathHelper().shouldRemoveSemicolonContent()) {
//提取出路径里UriTemplateVariables变量后的参数，设置到request属性中，供@MatrixVariable使用
request.setAttribute(MATRIX_VARIABLES_ATTRIBUTE, extractMatrixVariables(request, uriVariables));
}
uriVariables = getUrlPathHelper().decodePathVariables(request, uriVariables);
}
request.setAttribute(BEST_MATCHING_PATTERN_ATTRIBUTE, bestPattern);
//将uriVariables设置到request属性中
request.setAttribute(URI_TEMPLATE_VARIABLES_ATTRIBUTE, uriVariables);
}2 MatrixVariableMethodArgumentResolver使用参数值
在MatrixVariableMethodArgumentResolver中解析@MatrixVariable注解的参数值，对应上述单个参数和多个参数的示例。
参数值的结果如图：
protected Object resolveName(String name, MethodParameter parameter, NativeWebRequest request) throws Exception {
//从request中获取pathParameters，结构如上图
Map<String, MultiValueMap<String, String>> pathParameters = (Map<String, MultiValueMap<String, String>>)
request.getAttribute(HandlerMapping.MATRIX_VARIABLES_ATTRIBUTE, RequestAttributes.SCOPE_REQUEST);
if (CollectionUtils.isEmpty(pathParameters)) {
return null;
}
MatrixVariable ann = parameter.getParameterAnnotation(MatrixVariable.class);
Assert.state(ann != null, "No MatrixVariable annotation");
//从注解里获取从哪一个路径参数下获取MatrixVariable值
String pathVar = ann.pathVar();
List<String> paramValues = null;
if (!pathVar.equals(ValueConstants.DEFAULT_NONE)) {
if (pathParameters.containsKey(pathVar)) {
//从pathParameters获取路径参数对应Map，再从map中获取MatrixVariable对应值
paramValues = pathParameters.get(pathVar).get(name);
}
}
else {
boolean found = false;
paramValues = new ArrayList<>();
//遍历pathParameters，根据MatrixVariable名称取匹配
for (MultiValueMap<String, String> params : pathParameters.values()) {
if (params.containsKey(name)) {
if (found) {
String paramType = parameter.getNestedParameterType().getName();
throw new ServletRequestBindingException(
"Found more than one match for URI path parameter '" + name +
"' for parameter type [" + paramType + "]. Use 'pathVar' attribute to disambiguate.");
}
paramValues.addAll(params.get(name));
found = true;
}
}
}
if (CollectionUtils.isEmpty(paramValues)) {
return null;
}
else if (paramValues.size() == 1) {
return paramValues.get(0);
}
else {
return paramValues;
}
}3 MatrixVariableMapMethodArgumentResolver使用参数值
解析@MatrixVariable注解的参数值，对应上述Map类型参数的示例。
public Object resolveArgument(MethodParameter parameter, @Nullable ModelAndViewContainer mavContainer,
NativeWebRequest request, @Nullable WebDataBinderFactory binderFactory) throws Exception {
@SuppressWarnings("unchecked")
//从request中获取pathParameters
Map<String, MultiValueMap<String, String>> matrixVariables =
(Map<String, MultiValueMap<String, String>>) request.getAttribute(
HandlerMapping.MATRIX_VARIABLES_ATTRIBUTE, RequestAttributes.SCOPE_REQUEST);
if (CollectionUtils.isEmpty(matrixVariables)) {
//不存在时，返回空的map
return Collections.emptyMap();
}
MultiValueMap<String, String> map = new LinkedMultiValueMap<>();
MatrixVariable ann = parameter.getParameterAnnotation(MatrixVariable.class);
Assert.state(ann != null, "No MatrixVariable annotation");
String pathVariable = ann.pathVar();
if (!pathVariable.equals(ValueConstants.DEFAULT_NONE)) {
//根据路径参数获取map
MultiValueMap<String, String> mapForPathVariable = matrixVariables.get(pathVariable);
if (mapForPathVariable == null) {
return Collections.emptyMap();
}
map.putAll(mapForPathVariable);
}
else {
//遍历所有路径参数的matrixVariables
for (MultiValueMap<String, String> vars : matrixVariables.values()) {
vars.forEach((name, values) -> {
for (String value : values) {
map.add(name, value);
}
});
}
}
return (isSingleValueMap(parameter) ? map.toSingleValueMap() : map);
}三、配置
在解析MatrixVariable变量的之前，有一个判断，检验UrlPathHelper中的removeSemicolonContent参数，removeSemicolonContent默认是true，默认不会提取MatrixVariable变量，因此需要设置为false，才能进入该分支。
if (!getUrlPathHelper().shouldRemoveSemicolonContent()) {
request.setAttribute(MATRIX_VARIABLES_ATTRIBUTE, extractMatrixVariables(request, uriVariables));
}配置：
@Configuration
public class ConfigurePathMatchConfig implements WebMvcConfigurer {
@Override
public void configurePathMatch(PathMatchConfigurer configurer) {
UrlPathHelper urlPathHelper = new UrlPathHelper();
//这里设置为false
urlPathHelper.setRemoveSemicolonContent(false);
configurer.setUrlPathHelper(urlPathHelper);
}
}这样，在RequestMappingHandlerMapping创建过程中，会回调configurePathMatch( )方法。
总结
本文简单介绍了@MatrixVariable注解的使用及原理。
来源：https://blog.csdn.net/RenshenLi/article/details/119393762