关于SpringMVC在Controller层方法的参数解析详解

使用版本：

spring-boot: 2.1.6.release

sping: 5.1.8.release

java: openjdk 11.0.13

自定义参数解析器

为了能够实现自定义参数解析器，只需要实现 handlermethodargumentresolver 并将添加到 webmvcconfigurer#addargumentresolvers 即可。

实现效果

下面以添加一个获取请求头的 client-type 参数为例进行是实现。定义注解 @clienttypemark 以及enum clienttype ，用于注入header中的值。

@target({elementtype.parameter})

@retention(retentionpolicy.runtime)

@documented

public @interface clienttypemark {

}

public enum clienttype {

    web,

    mobile,

    unknown

    ;

}

最终实现的效果为在controller的方法中，可以按照如下实现使用。

@restcontroller

@requestmapping("/client")

public class clienttypeendpoint {



    @getmapping("/cur")

    public clienttype getcurclienttype(@clienttypemark clienttype clienttype) {

        return clienttype;

    }

}

实现和配置

按照如下方法实现 handlermethodargumentresolver ，用于解析header中的 client-type 并转化为 clienttype 。

package io.github.donespeak.springbootsamples.web.common;

import org.apache.commons.lang3.stringutils;

import org.springframework.core.methodparameter;

import org.springframework.web.bind.support.webdatabinderfactory;

import org.springframework.web.context.request.nativewebrequest;

import org.springframework.web.method.support.handlermethodargumentresolver;

import org.springframework.web.method.support.modelandviewcontainer;

public class curclienttypemethodargumentresolver implements handlermethodargumentresolver {

    private final string[] client_type_header_names = {"client-type", "client-type", "client-type"};

    // 选择要被注入的参数：判断参数是否符合解析的条件

    @override

    public boolean supportsparameter(methodparameter param) {

        return param.hasparameterannotation(clienttypemark.class)

                && clienttype.class.isassignablefrom(param.getparametertype());

    }

    // 返回值将被注入到被选中参数中

    @override

    public object resolveargument(methodparameter methodparameter, modelandviewcontainer modelandviewcontainer,

            nativewebrequest nativewebrequest, webdatabinderfactory webdatabinderfactory) throws exception {

        string clienttype = null;

        for (string clienttypeheader: client_type_header_names) {

            clienttype = nativewebrequest.getheader(clienttypeheader);

            if (stringutils.isnotblank(clienttype)) {

                break;

            }

        }

        try {

            return stringutils.isblank(clienttype) ? clienttype.unknown : clienttype.valueof(clienttype.touppercase());

        } catch (exception e) {

            return clienttype.unknown;
        }
    }
}

为了使得配置能够生效，可以按照如下的方法添加解析器。

@configuration
public class webmvcconfig implements webmvcconfigurer {
    @override
    public void addargumentresolvers(list<handlermethodargumentresolver> argumentresolvers) {

        // 解析@curuserid注解的参数

        argumentresolvers.add(new curclienttypemethodargumentresolver());

    }

}

至此，自定义参数解析器的工作就完成了。

spring提供解析器

当你完成上面的自定义解析器的时候，大体就能知道spring在controller层的其他参数解析都是怎么实现的了。

如下是spring mvc默认的一些参数解析器。

package org.springframework.web.servlet.mvc.method.annotation;

public class requestmappinghandleradapter extends abstracthandlermethodadapter

        implements beanfactoryaware, initializingbean {

    ...

    /**

     * return the list of argument resolvers to use including built-in resolvers

     * and custom resolvers provided via {@link #setcustomargumentresolvers}.

     */

    private list<handlermethodargumentresolver> getdefaultargumentresolvers() {

        list<handlermethodargumentresolver> resolvers = new arraylist<>();

        // annotation-based argument resolution

        // 解析：@requestparam(required = false)

        resolvers.add(new requestparammethodargumentresolver(getbeanfactory(), false));

        // 解析：@requestparam map

        resolvers.add(new requestparammapmethodargumentresolver());

        // 解析：@pathvariable

        resolvers.add(new pathvariablemethodargumentresolver());

        // 解析：@pathvariable map

        resolvers.add(new pathvariablemapmethodargumentresolver());

        // 解析：@matrixvariable

        resolvers.add(new matrixvariablemethodargumentresolver());

        // 解析：@matrixvariable map

        resolvers.add(new matrixvariablemapmethodargumentresolver());

        // 解析：@modelattribute(required = false)

        resolvers.add(new servletmodelattributemethodprocessor(false));

        // 解析：@requestbody

        resolvers.add(new requestresponsebodymethodprocessor(getmessageconverters(), this.requestresponsebodyadvice));

        // 解析：@requestpart

        resolvers.add(new requestpartmethodargumentresolver(getmessageconverters(), this.requestresponsebodyadvice));

        // 解析：@requestheader

        resolvers.add(new requestheadermethodargumentresolver(getbeanfactory()));

        // 解析：@requestheader map

        resolvers.add(new requestheadermapmethodargumentresolver());

        // 解析：@cookievalue

        resolvers.add(new servletcookievaluemethodargumentresolver(getbeanfactory()));

        // 解析：@value

        resolvers.add(new expressionvaluemethodargumentresolver(getbeanfactory()));

        // 解析：@sessionattribute

        resolvers.add(new sessionattributemethodargumentresolver());

        // 解析：@requestattribute

        resolvers.add(new requestattributemethodargumentresolver());

        // type-based argument resolution

        // 解析：webrequest、servletrequest、multipartrequest、httpsession、

        //      principal、locale、timezone、java.time.zoneid、inputstream

        //      java.io.reader、org.springframework.http.httpmethod

        resolvers.add(new servletrequestmethodargumentresolver());

        // 解析：servletresponse、outputstream、writer

        resolvers.add(new servletresponsemethodargumentresolver());

        // 解析：@httpentity、@requestentity

        resolvers.add(new httpentitymethodprocessor(getmessageconverters(), this.requestresponsebodyadvice));

        // 解析：redirectattributes

        resolvers.add(new redirectattributesmethodargumentresolver());

        // 解析：org.springframework.ui.model, 值为modelandviewcontainer#getmodel

        resolvers.add(new modelmethodprocessor());

        // 解析：map, 值为modelandviewcontainer#getmodel

        resolvers.add(new mapmethodprocessor());

        // 解析：org.springframework.validation.errors

        resolvers.add(new errorsmethodargumentresolver());

        // 解析：org.springframework.web.bind.support.sessionstatus

        resolvers.add(new sessionstatusmethodargumentresolver());

        // 解析：uricomponentsbuilder 或者 servleturicomponentsbuilder

        resolvers.add(new uricomponentsbuildermethodargumentresolver());

        // custom arguments

        if (getcustomargumentresolvers() != null) {

            resolvers.addall(getcustomargumentresolvers());

        }

        // catch-all

        // 解析：@requestparam(required = true)

        resolvers.add(new requestparammethodargumentresolver(getbeanfactory(), true));

        // 解析：@modelattribute(required = true)

        resolvers.add(new servletmodelattributemethodprocessor(true));

        return resolvers;
    }
    ...

}

一些使用tricky

调整解析器的顺序

在一次使用spring security的开发中，定义的 userdetials 实现类在实现 userdetails 的同时还是实现了一个 account 接口，在使用时，希望实现如下的效果。

public void dosomething(@authenticationprincipal account accout) {}

但因为同时使用了，spring-data，spring-data提供的 proxyinghandlermethodargumentresolver 会在 authenticationprincipalargumentresolver 前面对account进行注入处理。proxyinghandlermethodargumentresolver 会拦截掉所有非org.springframework中定义的 接口 ，并尝试赋值。为了能够正常赋值给account，需要调整两者的位置。实现如下：

import java.util.linkedlist;

import java.util.list;

import org.springframework.beans.beansexception;

import org.springframework.beans.factory.config.beanpostprocessor;

import org.springframework.security.web.method.annotation.authenticationprincipalargumentresolver;

import org.springframework.stereotype.component;

import org.springframework.web.method.support.handlermethodargumentresolver;

import org.springframework.web.servlet.mvc.method.annotation.requestmappinghandleradapter;

/**

 * 将 authenticationprincipalargumentresolver 移到最前面，如果不做调整，

 * 会因为proxyinghandlermethodargumentresolver在authenticationprincipalargumentresolver前面，

 * 导致 @authenticationprincipal account account 无法注入

 */

public class argumentresolverbeanpostprocessor implements beanpostprocessor {

    private static final string bean_request_mapping_handler_adapter = "requestmappinghandleradapter";

    @override

    public object postprocessafterinitialization(object bean, string beanname) throws beansexception {

        if (beanname.equals(bean_request_mapping_handler_adapter)) {

            requestmappinghandleradapter adapter = (requestmappinghandleradapter)bean;

            list<handlermethodargumentresolver> argumentresolvers = adapter.getargumentresolvers();

            linkedlist<handlermethodargumentresolver> resolversadjusted = new linkedlist<>(argumentresolvers);

            argumentresolvers.stream().foreach(r -> {

                if (authenticationprincipalargumentresolver.class.isinstance(r)) {

                    resolversadjusted.addfirst(r);

                } else {

                    resolversadjusted.add(r);

                }
            });
adapter.setargumentresolvers(resolversadjusted);

        }
        return bean;
    }

} 

总结

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