SpringMVC学习笔记-实现文件上传

第一步：导入文件上传需要的包

commons-fileupload

详细的pom文件如下

<?xml version="1.0" encoding="UTF-8"?>

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>

  <groupId>com.zbt</groupId>
  <artifactId>spring</artifactId>
  <version>1.0-SNAPSHOT</version>
  <packaging>war</packaging>

  <name>spring Maven Webapp</name>
  <!-- FIXME change it to the project's website -->
  <url>http://www.example.com</url>

  <properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    <maven.compiler.source>1.8</maven.compiler.source>
    <maven.compiler.target>1.8</maven.compiler.target>
    <org.springframework-version>4.0.3.RELEASE</org.springframework-version>
    <org.aspectj-version>1.7.4</org.aspectj-version>
    <org.slf4j-version>1.7.5</org.slf4j-version>
    <hibernate.version>4.3.5.Final</hibernate.version>
    <c3p0.version>0.9.5.2</c3p0.version>
    <mysql.version>5.1.44</mysql.version>
    <taglibs.version>1.2.5</taglibs.version>
  </properties>

  <dependencies>
    <!--Spring-->
    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-context</artifactId>
      <version>${org.springframework-version}</version>
    </dependency>
    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-webmvc</artifactId>
      <version>${org.springframework-version}</version>
    </dependency>

    <!--Logging-->
    <dependency>
      <groupId>org.slf4j</groupId>
      <artifactId>slf4j-api</artifactId>
      <version>${org.slf4j-version}</version>
    </dependency>
    <dependency>
      <groupId>org.apache.commons</groupId>
      <artifactId>commons-lang3</artifactId>
      <version>3.4</version>
    </dependency>
    <dependency>
      <groupId>commons-fileupload</groupId>
      <artifactId>commons-fileupload</artifactId>
      <version>1.3.1</version>
    </dependency>
    <!--@Inject-->
    <dependency>
      <groupId>javax.inject</groupId>
      <artifactId>javax.inject</artifactId>
      <version>1</version>
    </dependency>
    <!--Servlet-->
    <dependency>
      <groupId>javax.servlet</groupId>
      <artifactId>servlet-api</artifactId>
      <version>2.5</version>
      <scope>provided</scope>
    </dependency>
    <dependency>
      <groupId>javax.servlet.jsp</groupId>
      <artifactId>jsp-api</artifactId>
      <version>2.1</version>
      <scope>provided</scope>
    </dependency>
    <dependency>
      <groupId>javax.servlet</groupId>
      <artifactId>jstl</artifactId>
      <version>1.2</version>
      <scope>provided</scope>

    </dependency>
    <dependency>
      <groupId>org.apache.taglibs</groupId>
      <artifactId>taglibs-standard-impl</artifactId>
      <version>${taglibs.version}</version>
    </dependency>
    <dependency>
      <groupId>org.apache.taglibs</groupId>
      <artifactId>taglibs-standard-jstlel</artifactId>
      <version>${taglibs.version}</version>
    </dependency>
  </dependencies>

  <build>
    <finalName>spring</finalName>
  </build>
</project>

第二步在SpringMVC中配置文件上传解析器

<bean id="multipartResolver" class="org.springframework.web.multipart.commons.CommonsMultipartResolver">
        <!--设置文件最大上传的大小-->
        <property name="maxUploadSize" value="100000"/>
</bean>

详细配置文件如下

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:context="http://www.springframework.org/schema/context"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd">
    <context:component-scan base-package="com.zbt.controller"/>
    <context:annotation-config/>
    <bean id="multipartResolver" class="org.springframework.web.multipart.commons.CommonsMultipartResolver">
        <property name="maxUploadSize" value="100000"/>
    </bean>
    <bean id="jspViewResolver" class="org.springframework.web.servlet.view.InternalResourceViewResolver">
        <property name="viewClass" value="org.springframework.web.servlet.view.JstlView"/>
        <property name="prefix" value="/WEB-INF/jsp/"/>
        <property name="suffix" value=".jsp"/>
    </bean>
</beans>

第三步在Controller中使用MultiPart 类型接受File文件

package com.zbt.controller;

import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.multipart.MultipartFile;

import java.io.IOException;

/**
 * Created by luckyboy on 2018/8/23.
 */
@Controller
@RequestMapping("/file")
public class FileUploadController {
    @RequestMapping(value="/upload",method= RequestMethod.POST)
    public String upload(@RequestParam("name")String name ,@RequestParam("file") MultipartFile file){
        if(file!= null){
            try {
                byte[] bytes = file.getBytes();
            }catch (IOException e) {
                e.printStackTrace();
            }
            return "success";
        }else{
            return "fail";
        }
    }
}

文件上传详解

DispactherServlet.doDispatch

    protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
        HttpServletRequest processedRequest = request;
        HandlerExecutionChain mappedHandler = null;
        boolean multipartRequestParsed = false;
        //由DispatcherServlet的checkMultipart(request)返回一个一个HttpprocessRequest子类MultipartHttpServletRequest
        processedRequest = checkMultipart(request);
        //如果是一个文件上传，processRequest != request
        multipartRequestParsed = processedRequest != request;
        //后面就是处理器映射了、视图渲染等操作
    }

DispactherServlet.checkMultipart

protected HttpServletRequest checkMultipart(HttpServletRequest request) throws MultipartException {
        //multipartResolver不为空，且由方法isMultipart(request)判断是文件上传，那么就解析request返回一个MultipartHttpServletRequest
        if (this.multipartResolver != null && this.multipartResolver.isMultipart(request)) {
            if (request instanceof MultipartHttpServletRequest) {
                logger.debug("Request is already a MultipartHttpServletRequest - if not in a forward, " +
                        "this typically results from an additional MultipartFilter in web.xml");
            }
            else {
                return this.multipartResolver.resolveMultipart(request);
            }
        }
        // If not returned before: return original request.
        return request;
    }

//MultipartResolver的一个子类调用CommonsMultipartResolver调用ServletFileUpload判断是否是文件
@Override
    public boolean isMultipart(HttpServletRequest request) {
        return (request != null && ServletFileUpload.isMultipartContent(request));
    }
//由ServletFileUpload调用FileUploadBase.isMultipartContent是否是文件上传
public static final boolean isMultipartContent(
            HttpServletRequest request) {
        if (!POST_METHOD.equalsIgnoreCase(request.getMethod())) {
            return false;
        }
        return FileUploadBase.isMultipartContent(new ServletRequestContext(request));
    }
//由FileUpload中的isMultipartContent从contentType中判断是否是文件上传，是则返回true，否则返回false
public static final boolean isMultipartContent(RequestContext ctx) {
        String contentType = ctx.getContentType();
        if (contentType == null) {
            return false;
        }
        if (contentType.toLowerCase(Locale.ENGLISH).startsWith(MULTIPART)) {
            return true;
        }
        return false;
    }

第一步：我们配置多路文件解析器，当一个请求到来时，在DispatcherServlet的doDispatcher会将HttpServletRequest进行一个校验
第二步：校验的工作是由MultipartResolver的一个子类CommonsMultipartResolver去调用一系列的方法最终从request的contentType来判断是否是一个文件上传，如果是则将request包装成一个MultipartHttpServletRequest
第三步：对包装后的MultipartMultipartHttpServletRequest进行处理