我的代碼中的空指針異常

Question

您好，正在使用MVC架構開發Web應用程序，試圖通過服務層將數據從表單插入數據庫，但會引發空指針異常：

以下是我的Servlet：

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    Affiliate af= new Affiliate();

    af.setFisrtName(request.getParameter("txtFname"));
    af.setLastName(request.getParameter("txtLname"));
    af.setGender(request.getParameter("txtGender"));
    af.setCategory(request.getParameter("txtCategory"));
    String dob=(request.getParameter("txtDob"));
    SimpleDateFormat formatter = new SimpleDateFormat("MM/dd/yyyy");  
    Date date;
    try {
        date = (Date)formatter.parse(dob);
        af.setDate(date);
    } catch (ParseException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

    af.setAge(Integer.parseInt(request.getParameter("txtAge")));
    af.setAddress(request.getParameter("txtAddr"));
    af.setCountry("India");
    af.setState(request.getParameter("txtState"));
    af.setCity(request.getParameter("txtCity"));
    af.setPinCode(Integer.parseInt(request.getParameter("txtPin")));
    af.setEmailId(request.getParameter("txtEmail"));
    af.setStd(Integer.parseInt(request.getParameter("txtStd")));
    af.setContactNo(Integer.parseInt(request.getParameter("txtPhone")));
    af.setMobileNo(Long.parseLong(request.getParameter("txtMobile"),10));

AffiliateService afs=new AffiliateService();
**afs.createAffiliate(af);**
}

}

我的服務代碼是：

public class AffiliateService {
    Affiliate affiliate=null;


    public Affiliate createAffiliate( Affiliate affiliate) {
         **validateAffiliate(affiliate);**
        return affiliate;
            }


    private Affiliate validateAffiliate(Affiliate affiliate) {
        this.affiliate=affiliate;
         if(affiliate!=null){
       AffiliateDAO afd=new AffiliateDAO();
        **afd.insertAffiliate(affiliate);**
    }
    return affiliate;

}


}

我的DAO代碼如下：

public class AffiliateDAO {

    private DataSource dataSource;
    public void setDataSource(DataSource dataSource) {
    this.dataSource = dataSource;
    }

    public List<Affiliate> addAffiliate(){
    ArrayList<Affiliate> affiliates = new ArrayList<Affiliate>();
    return affiliates;
          }



public void updateAffiliate(Affiliate affiliate){


}

public void delteAffiliate(Affiliate affiliate){

}

public void selectAffiliate(Affiliate affiliate){

}

public void insertAffiliate(Affiliate affiliate){
    String sql="INSERT INTO REGISTER " +"(id,FisrtName,LastName,Gender,Category,DateOfBirth,Age,Address,Country,State,City,PinCode,EmailId,Std,ContactNo,MobileNo)VALUES(?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?)";
    Connection conn = null;

    try {
        **conn = dataSource.createConnection();**
        PreparedStatement ps = conn.prepareStatement(sql);
        ps.setInt(1, affiliate.getId());
        ps.setString(2, affiliate.getFisrtName());
        ps.setString(3, affiliate.getLastName());
        ps.setString(4,affiliate.getGender());
        ps.setString(5, affiliate.getCategory());
        ps.setDate(6, (Date) affiliate.getDate());
        ps.setInt(7, affiliate.getAge());
        ps.setString(8, affiliate.getAddress());
        ps.setString(9,affiliate.getCountry());
        ps.setString(10,affiliate.getState());
        ps.setString(11, affiliate.getCity());
        ps.setInt(12, affiliate.getPinCode());
        ps.setString(13, affiliate.getEmailId());
        ps.setInt(14,affiliate.getStd());
        ps.setInt(15, affiliate.getContactNo());
        ps.setLong(16, affiliate.getMobileNo());

        ps.executeUpdate();
        ps.close();

    } catch (SQLException e) {
        throw new RuntimeException(e);

    } finally {
        if (conn != null) {
            try {
                conn.close();
            } catch (SQLException e) {}
        }
    }
}


public Affiliate searchById(int id){
    String sql = "SELECT * FROM REGISTER WHERE id = ?";

    Connection conn = null;

    try {
        conn = dataSource.createConnection();
        PreparedStatement ps = conn.prepareStatement(sql);
        ps.setInt(1, id);
        Affiliate affiliate = null;
        ResultSet rs = ps.executeQuery();
        if (rs.next()) {

                rs.getInt("id");
                rs.getString("FisrtName");
                rs.getString("LastName");
                rs.getString("Gender");
                rs.getString("Category");
                rs.getDate("DateOfBirth");
                rs.getString("Age");
                rs.getString("Address");
                rs.getString("Country");
                rs.getString("State");
                rs.getString("City");
                rs.getInt("PinCode");
                rs.getString("EmailId");
                rs.getInt("Std+ContactNo");
                rs.getString("MobileNo");
            }
        rs.close();
        ps.close();
        return affiliate;
    } catch (SQLException e) {
        throw new RuntimeException(e);
    } finally {
        if (conn != null) {
            try {
            conn.close();
            } catch (SQLException e) {}
        }

    }
}
}

這是我的dataSource類：

public class DataSource {

    Connection connection=null;
    BasicDataSource bdsource=new BasicDataSource();

    public DataSource(){

        bdsource.setUrl("dbUrl");
        bdsource.setUsername("dbuserName");
        bdsource.setPassword("dbPassword");
        bdsource.setDriverClassName("com.mysql.jdbc.Driver");
    }
    public Connection createConnection(){

        Connection con=null;


        try{

            if(connection !=null){
              System.out.println("Can't create a new connection");
            }
            else{
                con=bdsource.getConnection();
            }
        }
            catch(Exception e){
                e.printStackTrace();

        }
        return con;
    }
}

我的堆棧跟蹤如下：

    java.lang.NullPointerException
com.affiliate.DAO.AffiliateDAO.insertAffiliate(AffiliateDAO.java:43)
com.affiliate.service.AffiliateService.validateAffiliate(AffiliateService.java:21)
com.affiliate.service.AffiliateService.createAffiliate(AffiliateService.java:12)
com.affiliate.servlet.AffiliateServlet.doPost(AffiliateServlet.java:71)
javax.servlet.http.HttpServlet.service(HttpServlet.java:647)
javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:51)
com.affiliate.servlet.RegisterServlet.doPost(RegisterServlet.java:42)
javax.servlet.http.HttpServlet.service(HttpServlet.java:647)
javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:51)

代碼中所有加粗的行都對應於堆棧跟蹤。 請幫助我解決此問題。我懷疑我的驗證方法...

Answer 1

好像dataSource為null因為從未調用過setDataSource 。

Answer 2

您需要修改AffiliateService類的validateAffiliate(Affiliate affiliate)方法。 您從未初始化過導致NPE發生的數據源 。

檢查一下：

private Affiliate validateAffiliate(Affiliate affiliate) {
   this.affiliate=affiliate;
   if(affiliate!=null){
   AffiliateDAO afd=new AffiliateDAO();

   // This was causing NPE. Data source must be set before using it.
   afd.setDataSource(passDataSourceInstance);

   afd.insertAffiliate(affiliate);
}

Answer 3

在調用conn = dataSource.createConnection（）之前初始化dataSource。 可以在AffiliateDAO構造函數中。