文件上传之servlet3.0实现_jetty-maven-plugin servlet 3.0-优快云博客

本文链接：https://blog.youkuaiyun.com/shushanfx/article/details/51835620

文件上传之servlet3.0实现

标签（空格分隔）： java fileupload

本例使用servlet3.0实现文件上传，项目管理使用maven

pom.xml配置

<?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.shushanfx</groupId>
    <artifactId>servlet30</artifactId>
    <version>1.0-SNAPSHOT</version>
    <packaging>war</packaging>

    <dependencies>
        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>javax.servlet-api</artifactId>
            <version>3.1.0</version>
            <scope>provided</scope>
        </dependency>
    </dependencies>
    <build>
        <finalName>servlet30</finalName>
        <plugins>
            <plugin>
                <groupId>org.eclipse.jetty</groupId>
                <artifactId>jetty-maven-plugin</artifactId>
                <version>9.2.11.v20150529</version>
                <configuration>
                    <scanIntervalSeconds>10</scanIntervalSeconds>
                    <webApp>
                        <contextPath>/</contextPath>
                    </webApp>
                    <httpConnector>
                        <port>8888</port>
                    </httpConnector>
                </configuration>
            </plugin>
        </plugins>
    </build>
</project>

代码分析

导入servlet3.1的包，scope为provided，方便编译;
使用jetty作为启动服务，端口8888.

web.xml

web.xml内容基本上是没有用的

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
    xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
    version="2.5">

</web-app>

代码分析

注意此处的版本号使用的是2.5，如果使用2.4的话，jetty将无法识别Servlet3.0的注解

java代码

package com.shushanfx.servlet30;

import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.annotation.MultipartConfig;
import javax.servlet.annotation.WebInitParam;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.Part;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.Collection;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.List;

/**
 * Created by dengjianxin on 2016/7/4.
 */
@WebServlet(name = "uploadServlet", urlPatterns = "/upload.php",
        loadOnStartup = 1, initParams = {
        @WebInitParam(name = "name", value = "shushanfx提醒您<br />")
})
@MultipartConfig(
        location = "upload",  //文件存放路径，指定的目录必须存在，否则会抛异常
        maxFileSize = 8388608,  //最大上传文件大小,经测试应该是字节为单位
        fileSizeThreshold = 819200, //当数据量大于该值时，内容将被写入文件。（specification中的解释的大概意思，不知道是不是指Buffer size），大小也是已字节单位
        maxRequestSize = 8 * 1024 * 1024 * 6 //针对该 multipart/form-data 请求的最大数量，默认值为 -1，表示没有限制。以字节为单位。
)
public class UploadServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        req.setCharacterEncoding("UTF-8");
        resp.setCharacterEncoding("UTF-8");
        ServletConfig config = getServletConfig();
        PrintWriter out = resp.getWriter();
        out.println("<html>");
        out.println("<body>");
        out.println(config.getInitParameter("name"));
        out.println("<form id=\"upload-form\" action=\"upload.php\" method=\"post\" enctype=\"multipart/form-data\">\n" +
                "    <input type=\"file\" id=\"upload\" name=\"upload\" />\n" +
                "    <input type=\"submit\" value=\"Upload\" />\n" +
                "</form>");
        if(req.getAttribute("fileNames")!=null){
            out.println("fileNames -> ");
            List<String> list = (List<String>) req.getAttribute("fileNames");
            for(String item : list){
                out.print(item + "&nbsp;");
            }
            out.println("<br />");
        }
        out.println("</body>");
        out.println("</html>");
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        List<String> fileNames = new LinkedList<String>();
        req.setCharacterEncoding("UTF-8");
        Collection<Part> parts = req.getParts();
        //遍历所有的表单内容，将表单中的文件写入上传文件目录
        for (Iterator<Part> iterator = parts.iterator(); iterator.hasNext();) {
            Part part = iterator.next();
            //从Part的content-disposition中提取上传文件的文件名
            String fileName = part.getName();

            if(fileName!=null){
                fileNames.add(fileName + "|" + part.getSubmittedFileName() + "|" + part.getSize());
                part.write(fileName);
            }
        }
        req.setAttribute("fileNames", fileNames);
        //显示上传的文件列表
        doGet(req, resp);
    }
}

代码分析

使用Servlet3.0的注解功能，可以实现servlet/filter等自动注册；
使用MultipartConfig注解，系统在执行post之前解析body部分，分离文件和普通字段；
通过req.getParts()获取所有的上传列表；
遍历列表，每个文件代表一个Part对象。通过解析Part对象来实现对文件的读取。