java实现文件上传下载

本文实例为大家分享了java实现文件上传下载的具体代码，供大家参考，具体内容如下

一.上传

1.前端：

				?

									<form method="post" action="fileupload" enctype="multipart/form-data">

									　　<input type="file" name="uploadfile" />

									　　<br/>

									　　<input type="submit" value="上传" />

									</form>

2.后台：

				?

									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;

									import dao.filedao;

									@webservlet("/fileupload")

									public class fileupload extends httpservlet {

									  private static final long serialversionuid = 1l;

									  // 上传配置

									  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

									  public fileupload() {

									    super();

									  }

									  protected void doget(httpservletrequest request, httpservletresponse response) throws servletexception, ioexception {

									    request.setcharacterencoding("utf-8");

									    response.setcharacterencoding("utf-8");

									    response.setcontenttype("text/html;charset=utf-8");

									    printwriter out = response.getwriter();

									      if (!servletfileupload.ismultipartcontent(request)) {

									      // 如果不是则停止

									      out.println("error: 表单必须包含 enctype=multipart/form-data");

									      out.flush();

									      return;

									    }

									    // 配置上传参数

									    diskfileitemfactory factory = new diskfileitemfactory();

									    // 设置内存临界值 - 超过后将产生临时文件并存储于临时目录中

									    factory.setsizethreshold(memory_threshold);

									    // 设置临时存储目录

									    factory.setrepository(new file(system.getproperty("java.io.tmpdir")));

									    servletfileupload upload = new servletfileupload(factory);

									    // 设置最大文件上传值

									    upload.setfilesizemax(max_file_size);

									    // 设置最大请求值 (包含文件和表单数据)

									    upload.setsizemax(max_request_size);

									    // 中文处理

									    upload.setheaderencoding("utf-8"); 

									    string uploadpath = request.getservletcontext().getrealpath("/files");

									    file uploaddir = new file(uploadpath);

									    if (!uploaddir.exists()) {

									      uploaddir.mkdir();

									    }

									    try {

									      // 解析请求的内容提取文件数据

									      list<fileitem> formitems = upload.parserequest(request);

									      if (formitems != null && formitems.size() > 0) {

									        // 迭代表单数据

									        for (fileitem item : formitems) {

									          // 处理不在表单中的字段

									          if (!item.isformfield()) {

									            string filename = new file(item.getname()).getname();

									            string filepath = uploadpath + file.separator + filename;

									            file storefile = new file(filepath);

									            // 在控制台输出文件的上传路径

									//            system.out.println(filepath);

									            // 保存文件到硬盘

									            if(storefile.exists()) {

									              out.println("上传失败，文件已存在！");

									            }else {

									              item.write(storefile);

									              out.println("文件上传成功!");

									            }  

									          }

									        }

									      }

									    } catch (exception ex) {

									      response.getwriter().println("文件上传成功!");

									    }

									  }

									  protected void dopost(httpservletrequest request, httpservletresponse response) throws servletexception, ioexception {

									    doget(request, response);

									  }

									}

二.下载

1.下载链接：

filedownload?filename="+urlencoder.encode(filename,"utf-8")　--------- 需要对url中的中文参数进行编码，否则会出现乱码

2.后台：

				?

									import java.io.file;

									import java.io.fileinputstream;

									import java.io.ioexception;

									import java.io.printwriter;

									import java.net.urlencoder;

									import javax.servlet.servletexception;

									import javax.servlet.annotation.webservlet;

									import javax.servlet.http.httpservlet;

									import javax.servlet.http.httpservletrequest;

									import javax.servlet.http.httpservletresponse;

									@webservlet("/filedownload")

									public class filedownload extends httpservlet {

									  private static final long serialversionuid = 1l;

									  public filedownload() {

									    super();

									  }

									  protected void doget(httpservletrequest request, httpservletresponse response) throws servletexception, ioexception {

									    request.setcharacterencoding("utf-8");

									    response.setcharacterencoding("utf-8");

									    printwriter out = response.getwriter();

									    string dirpath = request.getservletcontext().getrealpath("/files");

									    string filename = urlencoder.encode(request.getparameter("filename"),"utf-8");  //需要对url中的中文参数进行编码，否则出现乱码

									    response.getwriter().println(filename);

									    string filepath = dirpath + file.separator + filename;

									    response.setcontenttype("application/octet-stream");

									    response.setheader("content-disposition", "attachment; filename=\"" + filename + "\"");

									    fileinputstream fileinputstream = new fileinputstream(filepath);

									    int i = 0;

									    while ((i = fileinputstream.read()) != -1) {

									      out.write(i);

									    }

									    fileinputstream.close();

									    out.close();

									  }

									  protected void dopost(httpservletrequest request, httpservletresponse response) throws servletexception, ioexception {

									    doget(request, response);

									  }

									}