Question

我尝试将参数从servlet发送到db，我的连接中出现错误。

我的工作步骤：

在eclipse中，我使用Tomcat服务器
创建一个模型（没有任何技术，如Spring，Hibernate，JSP，JSF等），以便与DML方法一起使用（清除java代码）。
我测试了创建的模块（通过使用一些主要的测试类）并且它工作得很好（连接，插入，删除..）。
之后，我可以为客户端提供一个简单的HTML文档。

逐步运行Web模块的过程：

在开始Web项目之前，我开始运行Derby DB - 工作正常。
使用Apache Tomcat启动Web项目。
将数据插入HTML并提交。 - 工作正常
在Servlet类中，数据被门控到doGet（...）方法。 - 工作正常。
当我尝试将参数发送到DB时，从Servlet（doGet（...）方法）我的conector类中出现错误。

我该如何正确设置？感谢。

代码：

Servlet类：

@WebServlet({ "/StudentServlet", "/Student" })
public class StudentServlet extends HttpServlet {
        private static final long serialVersionUID = 1L;

        private StudentDbDao sf = new StudentDbDao();
        private Student student = new Student();

        protected void doGet(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {

        PrintWriter writer = response.getWriter();

        String studentId = request.getParameter("sudentId");
        Long id = Long.parseLong(studentId);

        String studentFullName = request.getParameter("studentFullName");

        String studentGendre = request.getParameter("studentGendre");

        String studentGrade = request.getParameter("studentGrade");

        try {
            student.setId(id);
            student.setFullName(studentFullName);
            student.setGender(studentGendre);
            student.setGrade(studentGrade);

            sf.createStudent(student);
            writer.println("The student #" + id + " inserted.");
                } catch (StudentSystemException e) {
            e.printStackTrace();
        }
    }
}

类StudentDbDao对DML功能的响应：

package dao.Db;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import bean.Student;
import bean.StudentSystemException;
import dao.StudentDao;
import dao.connector.ConnectionPool;

public class StudentDbDao implements StudentDao {

    private Connection conn;

    public StudentDbDao() {
    }

    @Override
    public void createStudent(Student student) throws StudentSystemException {

    conn = ConnectionPool.getInstance().getConnection();
    String sql = "INSERT INTO Students(ID, FULLNAME, GENDER, GRADE) VALUES(?, ?, ?, ?)";
    PreparedStatement pstmt;

    try {
        pstmt = conn.prepareStatement(sql);

        pstmt.setLong(1, student.getId());
        pstmt.setString(2, student.getFullName());
        pstmt.setString(3, student.getGender());
        pstmt.setString(4, student.getGrade());

        pstmt.executeUpdate();

        System.out.println(student.getFullName() + " created successfully");

    } catch (SQLException e) {
        throw new StudentSystemException("Failed!", e);
    } finally {
        ConnectionPool.getInstance().returnConnection(conn);
    }

    }

@Override
public void removeStudent(Student student) throws StudentSystemException {
    conn = ConnectionPool.getInstance().getConnection();
    String sql = "DELETE FROM Students WHERE ID = " + student.getId();
    PreparedStatement pstmt;

    try {
        pstmt = conn.prepareStatement(sql);
        pstmt.executeUpdate();
        System.out.println(student.getId() + " removed successfully.");

    } catch (SQLException e) {
        throw new StudentSystemException("Failed!", e);
    } finally {
        ConnectionPool.getInstance().returnConnection(conn);
    }
}

@Override
public Student getStudentById(long id) throws StudentSystemException {

    conn = ConnectionPool.getInstance().getConnection();
    String sql = "SELECT * FROM Students WHERE ID = " + id;
    Student student = new Student();
    PreparedStatement pstmt;
    ResultSet rs;

    try {
        pstmt = conn.prepareStatement(sql);
        rs = pstmt.executeQuery();

        if (rs.next()) {
            student.setId(rs.getLong(1));
            student.setFullName(rs.getString(2));
            student.setGender(rs.getString(3));
            student.setGrade(rs.getString(4));
        }
    // else {
    // System.out.print("Student with PID #" + id + " not exists. ");
    // }
        return student;

    } catch (SQLException e) {
        throw new StudentSystemException("Failed!", e);
    } finally {
        ConnectionPool.getInstance().returnConnection(conn);
    }

}

public long getMaxRows() throws StudentSystemException {

    conn = ConnectionPool.getInstance().getConnection();
    String sql = "SELECT COUNT(*) FROM Students";
    PreparedStatement pstmt;
    int count = 0;

    try {
        pstmt = conn.prepareStatement(sql);
        ResultSet rs = pstmt.executeQuery();

        rs.next();
        count = rs.getInt(1);
    } catch (SQLException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } finally {
        ConnectionPool.getInstance().returnConnection(conn);
    }

    return count;
}
}

类ConnectionPool，当Servlet尝试设置参数时代码落在其中：

public class ConnectionPool {

// static final int MAX_CONS = 1;
private Connection myconn = null;
// private Set<Connection> connections = new HashSet<Connection>();
private static ConnectionPool instance = new ConnectionPool();
String url = "jdbc:derby://localhost:1527/StudentDB";

private ConnectionPool() {

    try {
        myconn = DriverManager.getConnection(url);
    } catch (SQLException e) {
        e.printStackTrace();
    }
}

public static ConnectionPool getInstance() {
    return instance;
}

public Connection getConnection() {
    // Connection conn = myconn;
    return this.myconn;
}

public void returnConnection(Connection conn) {
    this.myconn = conn;
    // myconn.add(conn);
}

public void closeAllConnections() throws StudentSystemException {

    Connection connection = myconn;

    try {
        connection.close();
    } catch (SQLException e) {
        throw new StudentSystemException("Failed to close connection: ", e);
    }

}

在提交之前和打印屏幕之后附上：

之前：后：

JDBC：不能使用servlet和Apache Tomcat

0 个答案: