使用Java Servlet从数据库上传和下载文件

发布时间：2023-04-01 11:15:53 所属栏目：教程来源：

导读：在本文档中，我将指导您上载文件并将其存储在数据库中数据类型为BLOB的列中，然后从数据库中数据类型为BLOB的列中下载文件。

创建数据库

您可以使用任何数据库，下面是用于创建upload表的脚本，该表用于存储您

在本文档中，我将指导您上载文件并将其存储在数据库中数据类型为BLOB的列中，然后从数据库中数据类型为BLOB的列中下载文件。

创建数据库

您可以使用任何数据库，下面是用于创建upload表的脚本，该表用于存储您上载的数据文件。

CREATE TABLE `upload` (
   `id` VARCHAR(50) NOT NULL DEFAULT '' COLLATE 'utf8mb4_unicode_ci',`file` LONGBLOB NOT NULL,`filename` VARCHAR(255) NOT NULL DEFAULT '' COLLATE 'utf8mb4_unicode_ci',PRIMARY KEY (`id`) USING BTREE
)
COLLATE='utf8mb4_unicode_ci'
ENGINE=InnoDB
;
上传文件并存储在数据库中

fileupload.jsp

<%@ page language="java" pageEncoding="UTF-8"%>
<%@ page contentType="text/html;charset=UTF-8"%>
<%
request.setCharacterEncoding("UTF-8");
response.setCharacterEncoding("UTF-8");
response.setContentType("text/html; charset=UTF-8");
%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" >

<html>
<head>
<title>文件上传到数据库</title>
<Meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
</head>
<body>
<form method="POST" action="FileUpload" enctype="multipart/form-data" >
           <table>
       <tr><td>Id</td>
           <td><input type="text" name="id" /></td>
       <tr>
           <td>File</td>
            <td><input type="file" name="file" id="file" /> </td>
       </tr>
       <tr>
   <td colspan="2">
   <input type="submit" value="Upload" name="upload" id="upload" /> </td>
   </tr>
    </table>
</form>
</body>
</html>
FileUpload.java

//中文

import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.sqlException;
import java.sql.Statement;

import javax.servlet.servletexception;
import javax.servlet.annotation.MultipartConfig;
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;

@WebServlet("/FileUpload")
@MultipartConfig
public class FileUpload extends HttpServlet {

/**
*
*/
private static final long serialVersionUID = 1L;

protected void doPost(HttpServletRequest request,HttpServletResponse response)throws servletexception,IOException {
request.setCharacterEncoding("UTF-8");
response.setCharacterEncoding("UTF-8");
response.setContentType("text/html; charset=UTF-8");

final Part filePart = request.getPart("file");
String id = request.getParameter("id");

InputStream FileBytes = null;
final PrintWriter writer = response.getWriter();

try {

//if (!filePart.getContentType().equals("image/jpeg"))
// {
// writer.println("<br/> Invalid File");
// return;
// }

// else if (filePart.getSize()>1048576 ) { //2mb
// {
// writer.println("<br/> File size too big");
// return;
// }
// }

   String filename = filePart.getSubmittedFileName();
   FileBytes = filePart.getInputStream(); // to get the body of the request as binary data

final byte[] bytes = new byte[FileBytes.available()];
FileBytes.read(bytes); //Storing the binary data in bytes array.

Connection con=null;
Statement stmt=null;

try {
Class.forName("com.MysqL.cj.jdbc.Driver");
con = DriverManager.getConnection("jdbc:MysqL://localhost:3306/test?autoReconnect=true&useSSL=false&useUnicode=true&characterEncoding=UTF-8&serverTimezone=UTC","root","root");
} catch (Exception e) {
System.out.println(e);
System.exit(0);
}
int success=0;
PreparedStatement pstmt = con.prepareStatement("INSERT INTO upload VALUES(?,?,?)");
pstmt.setString(1,id);
pstmt.setBytes(2,bytes); //Storing binary data in blob field.
pstmt.setString(3,filename); //Storing binary data in blob field.
success = pstmt.executeUpdate();
if(success>=1) System.out.println("Data Stored");
con.close();

writer.println("<br/> Book Successfully Stored");

} catch (FileNotFoundException fnf) {
writer.println("You did not specify a file to upload");
writer.println("<br/> ERROR: " + fnf.getMessage());

} catch (sqlException e) {
// Todo Auto-generated catch block
e.printstacktrace();
} finally {

if (FileBytes != null) {
FileBytes.close();
}
if (writer != null) {
writer.close();
}
}

}

}
使用Stream

//中文
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.sqlException;
import java.sql.Statement;
import javax.servlet.servletexception;
import javax.servlet.annotation.MultipartConfig;
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;
@WebServlet("/FileUpload")
@MultipartConfig
public class FileUpload extends HttpServlet {
/**
*
*/
private static final long serialVersionUID = 1L;
protected void doPost(HttpServletRequest request,HttpServletResponse response) throws servletexception,IOException {
request.setCharacterEncoding("UTF-8");
response.setCharacterEncoding("UTF-8");
response.setContentType("text/html; charset=UTF-8");
final Part filePart = request.getPart("file");
String id = request.getParameter("id");
InputStream FileBytes = null;
final PrintWriter writer = response.getWriter();
Connection con = null;
Statement stmt = null;
try {
//if (!filePart.getContentType().equals("image/jpeg"))
// {
// writer.println("<br/> Invalid File");
// return;
// }
// else if (filePart.getSize()>1048576 ) { //2mb
// {
// writer.println("<br/> File size too big");
// return;
// }
// }
String filename = filePart.getSubmittedFileName();
FileBytes = filePart.getInputStream(); // to get the body of the request as binary data
try {
Class.forName("com.MysqL.cj.jdbc.Driver");
con = DriverManager.getConnection("jdbc:MysqL://localhost:3306/test?autoReconnect=true&useSSL=false&useUnicode=true&characterEncoding=UTF-8&serverTimezone=UTC","root");
} catch (Exception e) {
System.out.println(e);
System.exit(0);
}
int success = 0;
PreparedStatement pstmt = con.prepareStatement("INSERT INTO upload VALUES(?,?)");
pstmt.setString(1,id);
pstmt.setBinaryStream(2,FileBytes); //Storing binary data in blob field.
pstmt.setString(3,filename); //Storing binary data in blob field.
success = pstmt.executeUpdate();
if (success >= 1) System.out.println("Data Stored");
con.close();
writer.println("<br/> File Successfully Uploaded");
} catch (FileNotFoundException fnf) {
writer.println("You did not specify a file to upload");
writer.println("<br/> ERROR: " + fnf.getMessage());
} catch (sqlException e) {
// Todo Auto-generated catch block
e.printstacktrace();
} finally {
if (con != null) {
// closes the database connection
try {
con.close();
} catch (sqlException ex) {
ex.printstacktrace();
}
}
if (FileBytes != null) {
FileBytes.close();
}
if (writer != null) {
writer.close();
}
}
}
}
从数据库中下载文件

download.jsp

<%@ page language="java" pageEncoding="UTF-8"%>
<%@ page contentType="text/html;charset=UTF-8"%>
<%
request.setCharacterEncoding("UTF-8");
response.setCharacterEncoding("UTF-8");
response.setContentType("text/html; charset=UTF-8");
%>
<!DOCTYPE html>
<html>
<head>
<Meta charset="ISO-8859-1">
<title>从数据库下载文件</title>
</head>
<body>
   <form action="DBFileDownload" method="get">
       <input type="text" name="id">
       <input type="submit" value="getfile">
       </form>
</body>
</html>
DBFileDownloadServlet.java

//中文

import java.io.IOException;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.sqlException;

import javax.servlet.servletexception;
import javax.servlet.ServletoutputStream;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.net.URLEncoder;

/**
* Servlet implementation class GetDetails
*/
@WebServlet("/DBFileDownload")
public class DBFileDownloadServlet extends HttpServlet {
private static final long serialVersionUID = 1L;

protected void doGet(HttpServletRequest request,IOException {
request.setCharacterEncoding("UTF-8");
response.setCharacterEncoding("UTF-8");
response.setContentType("text/html; charset=UTF-8");

   String id = request.getParameter("id")!=null?request.getParameter("id"):"NA";

ServletoutputStream sos;
Connection con=null;
PreparedStatement pstmt=null;

sos = response.getoutputStream();

try {
Class.forName("com.MysqL.cj.jdbc.Driver");
con = DriverManager.getConnection("jdbc:MysqL://localhost:3306/test?autoReconnect=true&useSSL=false&useUnicode=true&characterEncoding=UTF-8&serverTimezone=UTC","root");
} catch (Exception e) {
System.out.println(e);
System.exit(0);
}

ResultSet rset=null;
try {
pstmt = con.prepareStatement("Select file,filename from upload where id=?");
System.out.println("Select file,filename from upload where id="+id.trim());
pstmt.setString(1,id.trim());
rset = pstmt.executeQuery();
if (rset.next()) {
response.setContentType("APPLICATION/OCTET-STREAM");

response.setHeader("Content-disposition","inline; filename*=UTF-8''" + URLEncoder.encode(rset.getString("filename"),"UTF-8"));
sos.write(rset.getBytes("file"));
   System.out.println(rset.getBytes("file"));
   System.out.println(rset.getString("filename"));
}
else
return;

} catch (sqlException e) {
// Todo Auto-generated catch block
e.printstacktrace();
}

sos.flush();
sos.close();

}

/**
* @see HttpServlet#doPost(HttpServletRequest request,HttpServletResponse response)
*/
protected void doPost(HttpServletRequest request,IOException {
// Todo Auto-generated method stub
}

}
使用Stream

//中文
import java.io.IOException;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.sqlException;
import java.sql.Statement;
import javax.servlet.servletexception;
import javax.servlet.ServletoutputStream;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.net.URLEncoder;
import java.io.InputStream;
/**
* Servlet implementation class GetDetails
*/
@WebServlet("/DBFileDownload")
public class DBFileDownloadServlet extends HttpServlet {
private static final long serialVersionUID = 1L;
protected void doGet(HttpServletRequest request,IOException {
request.setCharacterEncoding("UTF-8");
response.setCharacterEncoding("UTF-8");
response.setContentType("text/html; charset=UTF-8");
String id = request.getParameter("id") != null ? request.getParameter("id") : "NA";
ServletoutputStream sos;
Connection con = null;
PreparedStatement pstmt = null;
sos = response.getoutputStream();
ResultSet rset = null;
try {
try {
Class.forName("com.MysqL.cj.jdbc.Driver");
con = DriverManager.getConnection("jdbc:MysqL://localhost:3306/test?autoReconnect=true&useSSL=false&useUnicode=true&characterEncoding=UTF-8&serverTimezone=UTC","root");
} catch (Exception e) {
System.out.println(e);
System.exit(0);
}
pstmt = con.prepareStatement("Select file,filename from upload where id=?");
System.out.println("Select file,filename from upload where id=" + id.trim());
pstmt.setString(1,id.trim());
rset = pstmt.executeQuery();
if (rset.next()) {
response.setContentType("APPLICATION/OCTET-STREAM");
response.setHeader("Content-disposition","UTF-8"));
InputStream inputStream = rset.getBinaryStream("file");
int i;
while ((i = inputStream.read()) != -1) {
sos.write(i);
}
System.out.println(rset.getBytes("file"));
System.out.println(rset.getString("filename"));
} else
return;
} catch (sqlException e) {
// Todo Auto-generated catch block
e.printstacktrace();
} finally {
if (con != null) {
// closes the database connection
try {
con.close();
} catch (sqlException ex) {
ex.printstacktrace();
}
}
}
sos.flush();
sos.close();
}
/**
* @see HttpServlet#doPost(HttpServletRequest request,IOException {
// Todo Auto-generated method stub
}
}
使用Stream消耗内存少于使用字节数组。

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