java - 将文件从 JSP 发送到调用接口(interface)方法的 Controller - 如何从该请求上传文件？

Question

大家好，我正在从事一个项目。

希望你能帮助我解决我的问题..我已经挣扎了5天了!!

在分配给我的模块中，我必须将文件、标题、类别、上传详细信息从 JSP 上传到存储请求和响应的controller.do > 在名为 execute() 的方法中，该方法存在于 Command.java Interface 中。

现在，当我传递所有上传表单详细信息时，它会一直转到一个名为 ResourceCommand.java Implements Command 的类，该类调用 DAO 并在中间停止执行!!!!

来自Upload.jsp的部分代码

<form name="myform_up" method="post" action = "Controller">  
         <input type="hidden" name="form_action" value="resource" /> 
         <input type="hidden" name="action" value="insert" />
   <table>      
         <tr>
            <td>Document Title <font color="red">*</font></td></tr>
        <tr>
            <td><input type="text" name="name" /></td></tr>
        <tr>
            <td>Category <font color="red">*</font>
            <select name="cat">
                <option value="Java" selected >Java Material</option>
                <option value="Net">.Net Material</option>
                <option value="C">C and C# Material</option>
            </select></td>
        </tr>
            <input type="hidden" name="uploadedby" value="<jsp:getProperty name="userBean" property="user" />" />
        <tr>
            <td>Upload A file:
            <input type="file" name="file1"/></td>
        </tr>
        <tr>
            <td><br/><input type="checkbox" name="t_condition" checked />I Had received Copyrights for this Document</td>
        </tr>
        <TR>
            <td ALIGN="CENTER"><br/>
            <INPUT class="button blue" TYPE="submit" value="Upload" /> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
            <INPUT class="button red" TYPE="reset" value="Clear" />
            </td></TR>
    </TABLE>
</FORM>

来自Controller.java的部分代码

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("resource", new ResourceCommand());

    }

    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 {

        String formAction = request.getParameter("form_action");
System.out.println("implementing formAction = " + formAction);
        Commands command = (Commands) commands.get(formAction);     
                             command.execute(request, response);            
    }
}

来自ResourceCommand.java的部分代码

public class ResourceCommand extends HttpServlet  implements Commands{
    private static final long serialVersionUID = 1L;
    public void execute(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

        if ("insert".equalsIgnoreCase(request.getParameter("action"))) {
            this.addResource(request, response);
        }
    }

    private void addResource(HttpServletRequest request,
            HttpServletResponse response) throws ServletException, IOException{

        ResourceBean ResourceBean = new ResourceBean();
        mapToResourceBeans(request, ResourceBean);

        String result = null;
        try {
            result = new ResourceDAO().uploadResource(request, ResourceBean);
        } catch (Exception ex) {
            System.err.println(" Error in inserting new resource");
        }
        if ("success".equalsIgnoreCase(result)) {
                       // if Block CODE
        }

        else {
                       //Else block CODE
        }       
    }
    private void mapToResourceBeans(HttpServletRequest request,
            ResourceBean ResourceBean) {        
        ResourceBean.setName(request.getParameter("name"));
        ResourceBean.setCat(request.getParameter("cat"));
        ResourceBean.setUploadedby(request.getParameter("uploadedby"));             
    }   
}

来自Command.java的部分代码

public interface Commands {

    public void execute(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException;

}

来自ResourceDAO.java的部分代码

public class ResourceDAO {
        static final String SUCCESS = "success";
        static final String FAILURE = "failure";

        static Logger log = Logger.getLogger("com.a");

        public String uploadResource(HttpServletRequest request,
                ResourceBean newResource) throws FileNotFoundException {

            String result = null;
            PreparedStatement stmtInsert = null;    
            // Create a Database Connection
            Connection con = ConnectionDAO.getJDBCConnection();
            try {
            PreparedStatement pstmt = con
                        .prepareStatement("INSERT INTO resource(name, cat, uploadedby, file) values(?,?,?,?)");
                pstmt.setString(1, newResource.getName());
    System.out.println(newResource.getName());

                pstmt.setString(2, newResource.getCat());
    System.out.println(newResource.getCat());

                pstmt.setString(3, newResource.getUploadedby());
    System.out.println(newResource.getUploadedby());

                String file = request.getParameter("file1");
    System.out.println("0");

                File f = new File(file);
    System.out.println("1");

                FileInputStream fis = new FileInputStream(f);
    System.out.println("2");

                pstmt.setBinaryStream(4, fis, (int) f.length());
    System.out.println("3");    
                int rows = pstmt.executeUpdate();

                result = SUCCESS;

                if (rows != 1) { result = FAILURE; }

            } catch (SQLException ex) {
                result = FAILURE;
                ConnectionDAO.rollbackJDBCConnection(con);
                ex.printStackTrace();
            } finally {
                ConnectionDAO.commitJDBCConnection(con);
                ConnectionDAO.closeStatement(stmtInsert);
                ConnectionDAO.closeJDBCConnection(con);
            }
            return result;
        }    
    }

控制台显示..

implementing formAction = resource
 Error in inserting new resource
123
Net
null
0
1
i am going back to addResource page

如果我将 enctype="multipart/form-data" 放入表单 TAG.. 那么我会得到这个..

java.lang.NullPointerException
    com.kbcss.controller.Controller.processCommand(Controller.java:57)
    com.kbcss.controller.Controller.doPost(Controller.java:49)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:647)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:728) 

我完全迷失了..请帮助...

Answer 1

这是第 56 行吗？错误之前的那个？

Commands command = (Commands) commands.get(formAction);    

如果在 commands 映射(您没有显示)中找不到该命令，它可能会返回 null。您至少应该检查从 map 返回的有效命令。

当找不到匹配的内容时，Map 将返回 null。在下一行中，您使用它并会得到一个 NullPointerException。