我正在开发一个基于知识的社区共享系统的项目。 用户可以登录并将其资源共享给其他用户......
我在将文件上传到 mysql 数据库时遇到问题...
PS..我的老师严格要求使用MVC架构，所以，我必须使用相同的.. 所以我只创建了一个名为Controller.java 的Servlet。 这里我将重定向到其他java程序进行计算...
这是Controller.java的代码
package com.kbcss.controller;
import java.io.IOException;
import java.util.HashMap;
import java.util.Map;
import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import com.kbcss.command.LoginCommand;
import com.kbcss.command.Commands;
import com.kbcss.command.ResourceCommand;
import com.kbcss.command.UserCommand;
public class Controller extends HttpServlet {
private static final long serialVersionUID = 1L;
public Controller() {super();}
@SuppressWarnings("rawtypes")
private Map commands = new HashMap();
@SuppressWarnings("unchecked")
public void init(ServletConfig config) throws ServletException{
super.init();
System.out.println("i am in init");
this.commands.put("login", new LoginCommand());
this.commands.put("user", new UserCommand());
this.commands.put("resource", new ResourceCommand());
System.out.println("i am about to exit init");
}
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
System.out.println("i am in doget");
processCommand(request, response);
}
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
System.out.println("i am in dopost");
processCommand(request, response);
}
private void processCommand(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
System.out.println("i am in processCommand");
String formAction = request.getParameter("form_action");
System.out.println("i am in processCommand state 2");
Commands command = (Commands) commands.get(formAction);
command.execute(request, response);
System.out.println("i am about to exit processCommand");
}
}
这是将资源保存到我的数据库表的代码....名为ResourceCommand .java
package com.kbcss.command;
import java.io.*;
import java.util.*;
import javax.servlet.*;
import javax.servlet.http.*;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.sql.PreparedStatement;
import javax.naming.InitialContext;
import javax.naming.Context;
import javax.sql.DataSource;
import com.oreilly.servlet.MultipartRequest;
public class ResourceCommand extends HttpServlet implements Commands{
private static final long serialVersionUID = 1L;
public void execute(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
try {
//
// JNDI to connect to database
//
Connection conn = null;
Context initContext = new InitialContext();
Context envContext = (Context)initContext.lookup("java:/comp/env");
DataSource ds = (DataSource)envContext.lookup("jdbc/tia");
conn = ds.getConnection();
//
// Save file(s) temporarily to filesystem
//
MultipartRequest multi = new MultipartRequest(request, "F:", 10*1024*1024);
Enumeration files = multi.getFileNames();
String filename = "";
File f = null;
while(files.hasMoreElements()) {
String name = (String)files.nextElement();
filename = multi.getFilesystemName(name);
String type = multi.getContentType(name);
f = multi.getFile(name);
}
//
// Insert file into database
//
InputStream is = new FileInputStream(f);
String sql = "INSERT INTO resource (`title`, `cat`, `user`, `filename`, `file`, `like`) VALUES (?, ?, ?, ?, ?, ?)"
;
PreparedStatement stmt = conn.prepareStatement(sql);
// Set some Title
stmt.setString(1, "some thing");
// Set some category
stmt.setString(2, ".net");
// Set some user
stmt.setString(3, "sri");
// Set Filename
stmt.setString(4, f.getName());
// Set the data
stmt.setBinaryStream(5, is, (int) f.length());
// Set Likes
stmt.setInt(6, 2);
stmt.executeUpdate();
is.close();
//
// Release connection
//
if (stmt != null) {
try { stmt.close(); } catch (SQLException e) { ; }
stmt = null;
}
if (conn != null) {
try { conn.close(); } catch (SQLException e) { ; }
conn = null;
}
} catch(Exception e) {
System.out.println(e);
}
}
}
这是我将从中上传的jSP 文件...
<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
pageEncoding="ISO-8859-1"%>
<!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=ISO-8859-1">
<title>UPLOAD FILE page</title></head>
<body>
<form method="post" action="Controller" enctype="multipart/form-data">
<input type="hidden" name="form_action" value="resource" />
<b>File to upload to database:</b>
<input type="file" name="attachment" size="36">
<input type="submit" value="Upload">
</form>
</body></html>
这是我遇到的错误:(
INFO: Reloading Context with name [/KBCSS] is completed
i am in init
i am about to exit init
i am in dopost
i am in processCommand
i am in processCommand state 2
Oct 10, 2013 11:29:59 AM org.apache.catalina.core.StandardWrapperValve invoke
SEVERE: Servlet.service() for servlet [Controller] in context with path [/KBCSS] threw exception
java.lang.NullPointerException
at com.kbcss.controller.Controller.processCommand(Controller.java:69)
at com.kbcss.controller.Controller.doPost(Controller.java:53)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:647)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:222)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:123)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:472)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:171)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:99)
at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:953)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:408)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1023)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:589)
at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:312)
at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)
顺便说一句..我在这里创建了一个Command.java 接口(interface)。
package com.kbcss.command;
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.*;
public interface Commands {
public void execute(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException;
}
谁能指导一下我吗PLZZZZZZZZZZZZZZZZZZZ 我被困了一天半，不知道我在做什么......
如果你要求电气工程专业的学生做一个 Java 项目，就会发生这样的情况!!!!
非常感谢我这边......
最佳答案
很可能 commands.get(formAction); 返回 null，因此 command 也是 null 。当您调用 command.execute(request, response); 时，您正在尝试访问 null 对象中的某些内容。这将会给你带来一个NullPointerException。
使用打印语句来确定当您收到异常时 formAction 的确切值。然后验证您是否将该字符串的 key 放入 commands 中(如果它不是 "login"、"user" 或“资源”，因为您已经输入了这些)。
可能导致问题的另一件事是您需要将类类型添加到您的Map。将其更改为:
private Map<String,Command> commands = new HashMap<String,Command>();
执行此操作后，您不必取消 map 上的警告。
关于java - 调用传递请求和响应的方法将文件存储到 MYSQL 数据库时出错，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/19288456/