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