一. 注意事項
在Web應用中，文件上傳和下載功能是非常常用的功能，對於文件上傳，瀏覽器在上傳的過程中是將文件以流的形式提交到服務器端的
【文件上傳的注意事項】
- 為保證服務器安全，上傳文件應該放在外界無法直接訪問的目錄下，比如放於WEB-INF目錄下
- 為防止文件覆蓋的現象發生，要為上傳文件產生一個唯一的文件名
- 要限制上傳文件的最大值
- 可以限制上傳文件的類型，在收到上傳文件名時，判斷后綴名是否合法
二. 文件上傳步驟
1. 下載jar包
1-1.需要jar的地址：
https://mvnrepository.com/artifact/commons-io/commons-io
https://mvnrepository.com/artifact/commons-fileupload/commons-fileupload
1-2.在JavaWeb項目中導入jar包
1-3.【注意：使用IDEA導包需要注意修復路徑，將lib添加到項目輸出目錄】
2. 編寫upload.jsp
【注意：表單如果包含一個文件上傳輸入項的話
這個表單的enctype屬性就必須設置multipart/form-data】
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
<title>Title</title>
</head>
<body>
<form action="${pageContext.request.contextPath}/s"
method="post" enctype="multipart/form-data">
<p>上傳用戶：<input type="text" name="username"></p>
<p>上傳文件：<input type="file" name="file"></p>
<p><input type="submit"></p>
</form>
</body>
</html>
3. 代碼編寫 UploadFileServlet
import org.apache.commons.fileupload.FileItem;
import org.apache.commons.fileupload.FileUploadException;
import org.apache.commons.fileupload.ProgressListener;
import org.apache.commons.fileupload.disk.DiskFileItemFactory;
import org.apache.commons.fileupload.servlet.ServletFileUpload;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.util.List;
import java.util.UUID;
public class ServletUpload extends javax.servlet.http.HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
<span class="hljs-keyword">try</span> {
<span class="hljs-comment">//1.判斷上傳的文件是普通表單還是帶文件的表單</span>
<span class="hljs-keyword">if</span> (!ServletFileUpload.isMultipartContent(req)) {
<span class="hljs-keyword">return</span>;<span class="hljs-comment">//如果是普通文件，直接返回</span>
}<span class="hljs-comment">//通過if就是帶文件的表單</span>
<span class="hljs-comment">//2.創建上傳文件的保存路徑，建議在WEB-INF路徑下</span>
<span class="hljs-built_in">String</span> uploadPath = <span class="hljs-keyword">this</span>.getServletContext().getRealPath(<span class="hljs-string">"/WEB-INF/upload"</span>);
File uploadFile = <span class="hljs-keyword">new</span> File(uploadPath);
<span class="hljs-keyword">if</span> (!uploadFile.exists()) {
uploadFile.mkdirs();<span class="hljs-comment">//如果保存目錄不存在，就創建一個目錄</span>
}
<span class="hljs-comment">//3.創建臨時路徑</span>
<span class="hljs-built_in">String</span> tmpPath = <span class="hljs-keyword">this</span>.getServletContext().getRealPath(<span class="hljs-string">"/WEB-INF/tmp"</span>);
File tmpFile = <span class="hljs-keyword">new</span> File(tmpPath);
<span class="hljs-keyword">if</span> (!tmpFile.exists()) {
tmpFile.mkdirs();<span class="hljs-comment">//如果臨時目錄不存在，就創建一個目錄</span>
}
<span class="hljs-comment">//4.創建DiskFileItemFactory對象，處理文件上傳路徑或者大小限制的；</span>
DiskFileItemFactory <span class="hljs-keyword">factory</span> = getDiskFileItemFactory(tmpFile);
<span class="hljs-comment">//5.獲取ServletFileUpload</span>
ServletFileUpload upload = getServletFileUpload(<span class="hljs-keyword">factory</span>);
<span class="hljs-comment">//6.處理上傳的文件</span>
<span class="hljs-built_in">String</span> msg = uploadParseRequest(upload, req, uploadPath);
<span class="hljs-comment">//7.servlet請求轉發消息</span>
req.setAttribute(<span class="hljs-string">"msg"</span>,msg);
req.getRequestDispatcher(<span class="hljs-string">"msg.jsp"</span>).forward(req,resp);
} <span class="hljs-keyword">catch</span> (FileUploadException e) {
e.printStackTrace();
}
}
<span class="hljs-comment">//4.創建DiskFileItemFactory對象，處理文件上傳路徑或者大小限制的；</span>
public <span class="hljs-keyword">static</span> DiskFileItemFactory getDiskFileItemFactory(File tmpFile) {
DiskFileItemFactory <span class="hljs-keyword">factory</span> = <span class="hljs-keyword">new</span> DiskFileItemFactory();
<span class="hljs-comment">//4-1.設置一個緩沖區，當上傳文件大於這個緩沖區的時候，將它放在臨時文件中</span>
<span class="hljs-keyword">factory</span>.setSizeThreshold(<span class="hljs-number">1024</span> * <span class="hljs-number">1024</span>);
<span class="hljs-keyword">factory</span>.setRepository(tmpFile);<span class="hljs-comment">//4-2.臨時目錄的保存目錄</span>
<span class="hljs-keyword">return</span> <span class="hljs-keyword">factory</span>;
}
<span class="hljs-comment">//5.獲取ServletFileUpload</span>
public <span class="hljs-keyword">static</span> ServletFileUpload getServletFileUpload(DiskFileItemFactory <span class="hljs-keyword">factory</span>) {
ServletFileUpload upload = <span class="hljs-keyword">new</span> ServletFileUpload(<span class="hljs-keyword">factory</span>);
<span class="hljs-comment">//5-1.監聽文件上傳進度</span>
upload.setProgressListener(<span class="hljs-keyword">new</span> ProgressListener() {
<span class="hljs-meta">@Override</span>
<span class="hljs-comment">//5-2.l:已經讀取到文件的大小</span>
<span class="hljs-comment">//5-3.l1:文件大小</span>
public <span class="hljs-keyword">void</span> update(long l, long l1, <span class="hljs-built_in">int</span> i) {
System.out.println(<span class="hljs-string">"總大小:"</span> + l1 + <span class="hljs-string">"\t"</span> + <span class="hljs-string">"已上傳:"</span> + l);
}
});
upload.setHeaderEncoding(<span class="hljs-string">"utf-8"</span>);<span class="hljs-comment">//5-4.處理亂碼問題</span>
upload.setFileSizeMax(<span class="hljs-number">1024</span> * <span class="hljs-number">1024</span> * <span class="hljs-number">10</span>);<span class="hljs-comment">//5-5.設置單個文件的最大值</span>
upload.setSizeMax(<span class="hljs-number">1024</span> * <span class="hljs-number">1024</span> * <span class="hljs-number">10</span>);<span class="hljs-comment">//5-6.設置總共能夠上傳文件的大小</span>
<span class="hljs-keyword">return</span> upload;
}
<span class="hljs-comment">//6.處理上傳的文件</span>
public <span class="hljs-keyword">static</span> <span class="hljs-built_in">String</span> uploadParseRequest(ServletFileUpload upload, HttpServletRequest req, <span class="hljs-built_in">String</span> uploadPath)
throws FileUploadException, IOException {
<span class="hljs-built_in">String</span> msg = <span class="hljs-string">""</span>;
<span class="hljs-comment">//6-1.把前端請求解析，封裝成一個FileItem對象</span>
<span class="hljs-built_in">List</span><FileItem> fileItems = upload.parseRequest(req);
<span class="hljs-keyword">for</span> (FileItem fileItem : fileItems) {
<span class="hljs-keyword">if</span> (fileItem.isFormField()) {<span class="hljs-comment">//6-2.判斷上傳的文件是普通的表單還是帶文件的表單</span>
<span class="hljs-built_in">String</span> name = fileItem.getFieldName();
<span class="hljs-built_in">String</span> value = fileItem.getString(<span class="hljs-string">"utf-8"</span>);<span class="hljs-comment">//6-3.處理 亂碼</span>
} <span class="hljs-keyword">else</span> {<span class="hljs-comment">//6-4.判斷它是上傳文件</span>
<span class="hljs-comment">//6-5.拿到文件名字</span>
<span class="hljs-built_in">String</span> uploadFileName = fileItem.getName();
System.out.println(<span class="hljs-string">"上傳的文件名："</span> + uploadFileName);
<span class="hljs-keyword">if</span> (uploadFileName.trim().equals(<span class="hljs-string">""</span>) || uploadFileName == <span class="hljs-keyword">null</span>) {
<span class="hljs-keyword">continue</span>;
}
<span class="hljs-comment">//6-6.獲得上傳文件名</span>
<span class="hljs-built_in">String</span> fileName = uploadFileName.substring(uploadFileName.lastIndexOf(<span class="hljs-string">"/"</span>) + <span class="hljs-number">1</span>);
<span class="hljs-comment">//6-7.獲得文件的后綴名</span>
<span class="hljs-built_in">String</span> fileExtName = uploadFileName.substring(uploadFileName.lastIndexOf(<span class="hljs-string">"."</span>) + <span class="hljs-number">1</span>);
System.out.println(<span class="hljs-string">"文件信息 [文件名："</span> + fileName + <span class="hljs-string">"---文件類型"</span> + fileExtName + <span class="hljs-string">"]"</span>);
<span class="hljs-comment">//6-8.使用UUID(唯一識別的通用碼),保證文件名唯一</span>
<span class="hljs-built_in">String</span> uuidPath = UUID.randomUUID().toString();
<span class="hljs-comment">//6-9.文件真實存在的路徑 realPath</span>
<span class="hljs-built_in">String</span> realPath = uploadPath + <span class="hljs-string">"/"</span> + uuidPath;
<span class="hljs-comment">//6-10.給每個文件創建一個對應的文件夾</span>
File realPathFile = <span class="hljs-keyword">new</span> File(realPath);
<span class="hljs-keyword">if</span> (!realPathFile.exists()) {
realPathFile.mkdir();
}
<span class="hljs-comment">//6-11.獲得文件上傳的流</span>
InputStream inputStream = fileItem.getInputStream();
<span class="hljs-comment">//6-12.創建一個文件輸出流</span>
<span class="hljs-comment">//6-13.realPath = 真實的文件夾；</span>
<span class="hljs-comment">//6-14.差了一個文件; 加上輸出文件的名字+"/"+uuidFileName</span>
FileOutputStream fos = <span class="hljs-keyword">new</span> FileOutputStream(realPath + <span class="hljs-string">"/"</span> + fileName);
<span class="hljs-comment">//6-15.創建一個緩沖區</span>
byte[] buffer = <span class="hljs-keyword">new</span> byte[<span class="hljs-number">1024</span> * <span class="hljs-number">1024</span>];
<span class="hljs-comment">//6-16.判斷是否讀取完畢</span>
<span class="hljs-built_in">int</span> len = <span class="hljs-number">0</span>;
<span class="hljs-comment">//6-17.如果大於0說明還存在數據；</span>
<span class="hljs-keyword">while</span> ((len = inputStream.read(buffer)) > <span class="hljs-number">0</span>) {
fos.write(buffer, <span class="hljs-number">0</span>, len);
}
<span class="hljs-comment">//6-18.關閉流</span>
fos.close();
inputStream.close();
msg = <span class="hljs-string">"文件上傳成功！"</span>;
fileItem.delete();<span class="hljs-comment">//6-19.上傳成功，清除臨時文件</span>
}
}
<span class="hljs-keyword">return</span> msg;
}
<span class="hljs-meta">@Override</span>
protected <span class="hljs-keyword">void</span> doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req, resp);
}
}
4. 編寫msg.jsp
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
<title>Title</title>
</head>
<body>
${msg}
</body>
</html>
5. 配置web.xml
<servlet>
<servlet-name>ServletFileUpload</servlet-name>
<servlet-class>com.sz.ServletUpload</servlet-class>
</servlet>
<span class="hljs-tag"><<span class="hljs-name">servlet-mapping</span>></span>
<span class="hljs-tag"><<span class="hljs-name">servlet-name</span>></span>ServletFileUpload<span class="hljs-tag"></<span class="hljs-name">servlet-name</span>></span>
<span class="hljs-tag"><<span class="hljs-name">url-pattern</span>></span>/s<span class="hljs-tag"></<span class="hljs-name">url-pattern</span>></span>
<span class="hljs-tag"></<span class="hljs-name">servlet-mapping</span>></span>