Java JSP基礎文件上傳

前言

之前工作的時候, 經常聽人提及JSP與Java Servlet的概念. 本章就主要

本章涉及的例子都可以在https://github.com/SeanYanxml/arsenal/tree/master/arsenal-java/arsenal-servlet下找到.

如果你覺得我的項目不錯, 不妨給我一個Star. 你的支持就是我的動力.

前置準備

JDK
Maven
Eclipse
Tomcat
Maven依賴

<?xml version="1.0"?>
<project
	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"
	xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
	<modelVersion>4.0.0</modelVersion>
	<parent>
		<groupId>com.yanxml</groupId>
		<artifactId>arsenal-java-parent</artifactId>
		<version>0.0.1-SNAPSHOT</version>
	</parent>

	<groupId>com.yanxml</groupId>
	<artifactId>arsenal-jsp</artifactId>
	<version>0.0.1-SNAPSHOT</version>
	<name>arsenal-jsp</name>

	<properties>
		<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
	</properties>

	<dependencies>
		<!-- https://mvnrepository.com/artifact/javax.servlet/javax.servlet-api -->
		<dependency>
			<groupId>javax.servlet</groupId>
			<artifactId>javax.servlet-api</artifactId>
			<version>4.0.0</version>
			<scope>provided</scope>
		</dependency>

		<!-- https://mvnrepository.com/artifact/commons-fileupload/commons-fileupload -->
		<dependency>
			<groupId>commons-fileupload</groupId>
			<artifactId>commons-fileupload</artifactId>
			<version>1.3.3</version>
		</dependency>

		<!-- https://mvnrepository.com/artifact/commons-io/commons-io -->
		<dependency>
			<groupId>commons-io</groupId>
			<artifactId>commons-io</artifactId>
			<version>2.6</version>
		</dependency>

	</dependencies>
</project>

基本操作

upload.jsp

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
    "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>文件上傳實例</title>
</head>
<body>
<h1>文件上傳實例</h1>
<form method="post" action="/arsenal-jsp/UploadServlet" enctype="multipart/form-data">
    選擇一個文件:
    <input type="file" name="uploadFile" />
    <br/><br/>
    <input type="submit" value="上傳" />
</form>
</body>
</html>

與之前一樣的是, 需要在<form action="">處指定需要調用的api請求地址.

message.jsp

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
    "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>文件上傳結果</title>
</head>
<body>
    <center>
        <h2>${message}</h2>
    </center>
</body>
</html>

UploadServlet.java

import java.io.File;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.List;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.apache.commons.fileupload.FileItem;
import org.apache.commons.fileupload.disk.DiskFileItemFactory;
import org.apache.commons.fileupload.servlet.ServletFileUpload;

/**
 * Servlet implementation class UploadServlet
 */
@WebServlet("/UploadServlet")
public class UploadServlet extends HttpServlet{
	private static final long serialVersionUID = 1L;
    
    // 上傳文件存儲目錄
    private static final String UPLOAD_DIRECTORY = "upload";
 
    // 上傳配置
    private static final int MEMORY_THRESHOLD   = 1024 * 1024 * 3;  // 3MB
    private static final int MAX_FILE_SIZE      = 1024 * 1024 * 40; // 40MB
    private static final int MAX_REQUEST_SIZE   = 1024 * 1024 * 50; // 50MB
 
    /**
     * 上傳數據及保存文件
     */
    protected void doPost(HttpServletRequest request,
        HttpServletResponse response) throws ServletException, IOException {
        // 檢測是否爲多媒體上傳
        if (!ServletFileUpload.isMultipartContent(request)) {
            // 如果不是則停止
            PrintWriter writer = response.getWriter();
            writer.println("Error: 表單必須包含 enctype=multipart/form-data");
            writer.flush();
            return;
        }
 
        // 配置上傳參數
        DiskFileItemFactory factory = new DiskFileItemFactory();
        // 設置內存臨界值 - 超過後將產生臨時文件並存儲於臨時目錄中
        factory.setSizeThreshold(MEMORY_THRESHOLD);
        // 設置臨時存儲目錄
        factory.setRepository(new File(System.getProperty("java.io.tmpdir")));
 
        ServletFileUpload upload = new ServletFileUpload(factory);
         
        // 設置最大文件上傳值
        upload.setFileSizeMax(MAX_FILE_SIZE);
         
        // 設置最大請求值 (包含文件和表單數據)
        upload.setSizeMax(MAX_REQUEST_SIZE);
        
        // 中文處理
        upload.setHeaderEncoding("UTF-8"); 

        // 構造臨時路徑來存儲上傳的文件
        // 這個路徑相對當前應用的目錄
        String uploadPath = getServletContext().getRealPath("/") + File.separator + UPLOAD_DIRECTORY;
       
         
        // 如果目錄不存在則創建
        File uploadDir = new File(uploadPath);
        if (!uploadDir.exists()) {
            uploadDir.mkdir();
        }
 
        try {
            // 解析請求的內容提取文件數據
            @SuppressWarnings("unchecked")
            List<FileItem> formItems = upload.parseRequest(request);
 
            if (formItems != null && formItems.size() > 0) {
                // 迭代表單數據
                for (FileItem item : formItems) {
                    // 處理不在表單中的字段
                    if (!item.isFormField()) {
                        String fileName = new File(item.getName()).getName();
                        String filePath = uploadPath + File.separator + fileName;
                        File storeFile = new File(filePath);
                        // 在控制檯輸出文件的上傳路徑
                        System.out.println(filePath);
                        // 保存文件到硬盤
                        item.write(storeFile);
                        request.setAttribute("message",
                            "文件上傳成功!");
                    }
                }
            }
        } catch (Exception ex) {
            request.setAttribute("message",
                    "錯誤信息: " + ex.getMessage());
        }
        // 跳轉到 message.jsp
        getServletContext().getRequestDispatcher("/message.jsp").forward(
                request, response);
    }

}

此處和之前提及的Servlet教程一致, 都是繼承了HttpServlet. 並且實現了doPost()和doGet()方法.

文件上傳地址: http://localhost:8080/arsenal-jsp/upload.jsp

文件上傳後回覆:

Q&A

發佈後的包內缺少類org/apache/commons/fileupload/FileItemFactory

Caused by: org.apache.catalina.LifecycleException: Failed to start component [StandardEngine[Catalina].StandardHost[localhost].StandardContext[/arsenal-jsp]]
	at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:162)
	... 6 more
Caused by: java.lang.NoClassDefFoundError: org/apache/commons/fileupload/FileItemFactory
	at java.lang.Class.getDeclaredFields0(Native Method)
	at java.lang.Class.privateGetDeclaredFields(Class.java:2583)
	at java.lang.Class.getDeclaredFields(Class.java:1916)
	at org.apache.catalina.util.Introspection.getDeclaredFields(Introspection.java:106)
	at org.apache.catalina.startup.WebAnnotationSet.loadFieldsAnnotation(WebAnnotationSet.java:256)
	at org.apache.catalina.startup.WebAnnotationSet.loadApplicationServletAnnotations(WebAnnotationSet.java:132)
	at org.apache.catalina.startup.WebAnnotationSet.loadApplicationAnnotations(WebAnnotationSet.java:65)
	at org.apache.catalina.startup.ContextConfig.applicationAnnotationsConfig(ContextConfig.java:336)
	at org.apache.catalina.startup.ContextConfig.configureStart(ContextConfig.java:786)
	at org.apache.catalina.startup.ContextConfig.lifecycleEvent(ContextConfig.java:307)
	at org.apache.catalina.util.LifecycleSupport.fireLifecycleEvent(LifecycleSupport.java:95)
	at org.apache.catalina.util.LifecycleBase.fireLifecycleEvent(LifecycleBase.java:90)
	at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5213)
	at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:145)
	... 6 more
Caused by: java.lang.ClassNotFoundException: org.apache.commons.fileupload.FileItemFactory
	at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1333)
	at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1167)
	... 20 more

A: 因爲配置不當導致. 在發佈時加上Maven的依賴即可.

巧建Spring Web的Maven項目來解決java.lang.NoClassDefFoundError: org/apache/commons/fileupload/FileItemFactory

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Java JSP基礎 文件上傳

前言

前置準備

基本操作

Q&A

Java JSP基礎文件上傳