SpringMVC源码解读 - RequestMapping注解实现解读 - RequestCondition体系

一般我们开发时,使用最多的还是@RequestMapping注解方式.

@RequestMapping(value = "/", param = "role=guest", consumes = "!application/json")
public void myHtmlService() {
    // ...
}

台前的是RequestMapping ,正经干活的却是RequestCondition,根据配置的不同条件匹配request.

@RequestMapping注解,请看<SpringMVC源码解读 - HandlerMapping - RequestMappingHandlerMapping初始化>

典型的接口+模板.一个接口ReqeustCondition,一个抽象类,定义基础,然后n多的具体实现.

实现中可以分为3类:基础实现,外观类和容器.

　　其中CompositeRequestCondition和RequestMappingInfo本身不带任何的匹配条件,只是用于包装其他的RequestCondition进行匹配

基础实现:
　　consumes对应request的提交内容类型content type,如application/json, text/html

　　headers 对应http request 的请求头

　　params对应http request parameter

　　Patterns对应url,就是注解value中的配置

　　produces指定返回的内容类型的content type，仅当request请求头中的(Accept)类型中包含该指定类型才返回

　　requestMethods对应 http method,如GET,POST,PUT,DELETE等

外观类:

　　RequestConditionHolder,用于不知道具体是RequestCondition哪个子类时.自定义的条件,使用的这个进行封装

容器:

　　CompositeRequestCondition封装基础实现,具体的匹配都委托给基础实现类.

　　RequestMappingInfo,对应@RequestMapping注解,一一对应注解内容与基础实现,使用时一一委托.

先来看看RequestCondition的接口定义

 package org.springframework.web.servlet.mvc.condition;
     /**
      * The contract for request conditions.
      */
     public interface RequestCondition<T> {

         /**
          * 将不同的筛选条件合并
          */
         T combine(T other);

         /**
          * 根据request查找匹配到的筛选条件
          */
         T getMatchingCondition(HttpServletRequest request);

         /**
          * 不同筛选条件比较,用于排序
          */
         int compareTo(T other, HttpServletRequest request);

     }
 }

老规矩,接下来得上抽象类AbstractRequestCondition

AbstractRequestCondition做的事不多,覆写equals,hashCode,toString.实现equals,hashCode,toString时预留模板方法getContent();实现toString时预留模板方法getToStringInfix().

 package org.springframework.web.servlet.mvc.condition;
 /**
  * A base class for {@link RequestCondition} types providing implementations of
  * {@link #equals(Object)}, {@link #hashCode()}, and {@link #toString()}.
  *
  * @author Rossen Stoyanchev
  * @since 3.1
  */
 public abstract class AbstractRequestCondition<T extends AbstractRequestCondition<T>> implements RequestCondition<T> {

     /**
      * Return the discrete items a request condition is composed of.
      * For example URL patterns, HTTP request methods, param expressions, etc.
      * @return a collection of objects, never {@code null}
      */
     protected abstract Collection<?> getContent();

     @Override
     public boolean equals(Object o) {
         if (this == o) {
             return true;
         }
         if (o != null && getClass().equals(o.getClass())) {
             AbstractRequestCondition<?> other = (AbstractRequestCondition<?>) o;
             return getContent().equals(other.getContent());
         }
         return false;
     }

     @Override
     public int hashCode() {
         return getContent().hashCode();
     }

     @Override
     public String toString() {
         StringBuilder builder = new StringBuilder("[");
         for (Iterator<?> iterator = getContent().iterator(); iterator.hasNext();) {
             Object expression = iterator.next();
             builder.append(expression.toString());
             if (iterator.hasNext()) {
                 builder.append(getToStringInfix());
             }
         }
         builder.append("]");
         return builder.toString();
     }

     /**
      * The notation to use when printing discrete items of content.
      * For example " || " for URL patterns or " && " for param expressions.
      */
     protected abstract String getToStringInfix();

 }

接下来得看具体实现了,捏不到软柿子,用ParamsRequestCondition简单说明下子类吧

// ParamsRequestCondition

 // 保存解析出来的param匹配条件
 private final Set<ParamExpression> expressions;

ParamExpression其实很简单,看父类AbstractNameValueExpression很清楚

// AbstractNameValueExpression

 package org.springframework.web.servlet.mvc.condition;
 abstract class AbstractNameValueExpression<T> implements NameValueExpression<T> {
     // 参数的名字
     protected final String name;
     // 参数的值
     protected final T value;
     // 参数的匹配规则,是= 还是!=
     protected final boolean isNegated;
 }

到这里我们就可以看懂,使用ParamExpression保存param参数,这样可以任意多个.

combine的实现也就水到渠成,直接把expression拼接到一个集合里就行:

 package org.springframework.web.servlet.mvc.condition;
 public final class ParamsRequestCondition extends AbstractRequestCondition<ParamsRequestCondition> {
     /**
      * Returns a new instance with the union of the param expressions
      * from "this" and the "other" instance.
      */
     public ParamsRequestCondition combine(ParamsRequestCondition other) {
         Set<ParamExpression> set = new LinkedHashSet<ParamExpression>(this.expressions);
         set.addAll(other.expressions);
         return new ParamsRequestCondition(set);
     }
 }

getMatchingCondition时,只要有一个不符合就判定条件不匹配

 package org.springframework.web.servlet.mvc.condition;
 public final class ParamsRequestCondition extends AbstractRequestCondition<ParamsRequestCondition> {
     /**
      * Returns "this" instance if the request matches all param expressions;
      * or {@code null} otherwise.
      */
     public ParamsRequestCondition getMatchingCondition(HttpServletRequest request) {
         for (ParamExpression expression : expressions) {
             if (!expression.match(request)) {
                 return null;
             }
         }
         return this;
     }
 }

这边的match方法比较有意思,可以看下

 package org.springframework.web.servlet.mvc.condition;
 abstract class AbstractNameValueExpression<T> implements NameValueExpression<T> {
     public final boolean match(HttpServletRequest request) {
         boolean isMatch;
         if (this.value != null) {
             isMatch = matchValue(request);
         }
         else { // 没有value时,只要匹配name就好
             isMatch = matchName(request);
         }
         return isNegated ? !isMatch : isMatch; // 这边需要看仔细,=与!=的处理
     }

     protected abstract boolean matchName(HttpServletRequest request);

     protected abstract boolean matchValue(HttpServletRequest request);
 }

ParamExpression中给出matchName与matchValue的实现.

ParamExpression这里又是接口+抽象实现+模板方法设计模式,偷个懒,暂时不去关心各层抽象的什么.

compareTo根据匹配条件的多少来判定顺序

// ParamsRequestCondition

     public int compareTo(ParamsRequestCondition other, HttpServletRequest request) {
         return other.expressions.size() - this.expressions.size();
     }

记得还留有两个模板方法

getContent直接返回记录param的expressions

getToStringInfix则使用&&

// ParamsRequestCondition

     @Override
     protected Collection<ParamExpression> getContent() {
         return expressions;
     }

     @Override
     protected String getToStringInfix() {
         return " && ";
     }

再看看是如何解析param的

// ParamsRequestCondition

     /**
      * Create a new instance from the given param expressions.
      * @param params expressions with syntax defined in {@link RequestMapping#params()};
      *     if 0, the condition will match to every request.
      */
     public ParamsRequestCondition(String... params) {
         this(parseExpressions(params));
     }

     private static Collection<ParamExpression> parseExpressions(String... params) {
         Set<ParamExpression> expressions = new LinkedHashSet<ParamExpression>();
         if (params != null) {
             for (String param : params) {
                 expressions.add(new ParamExpression(param));
             }
         }
         return expressions;
     }

核心的代码还是在AbstractNameValueExpression

// AbstractNameValueExpression

逻辑不复杂,代码看着有点烦,是不是应该听Martin Fowler在<重构>中的建议,来个extract method?

     AbstractNameValueExpression(String expression) {
         int separator = expression.indexOf('=');
         if (separator == -1) {
             this.isNegated = expression.startsWith("!");
             this.name = isNegated ? expression.substring(1) : expression;
             this.value = null;
         }
         else {
             this.isNegated = (separator > 0) && (expression.charAt(separator - 1) == '!');
             this.name = isNegated ? expression.substring(0, separator - 1) : expression.substring(0, separator);
             this.value = parseValue(expression.substring(separator + 1));
         }
     }

RequestCondition的解读未完,待续:

SpringMVC源码解读 - RequestMapping注解实现解读 - ConsumesRequestCondition

SpringMVC源码解读 - RequestMapping注解实现解读 - RequestMappingInfo