classservlet.java

学生成绩管理系统JPA做的

package com.fengmanfei.student.servlet;

import java.io.IOException;
import java.util.List;

import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.EntityTransaction;
import javax.persistence.Persistence;
import javax.persistence.Query;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import com.fengmanfei.student.entity.ClassEO;
import com.fengmanfei.student.exception.StudentException;

public class ClassServlet extends HttpServlet {

	private static final long serialVersionUID = -8205614348005279786L;

	// @PersistenceUnit(unitName="student")
	private EntityManagerFactory emf;

	@Override
	public void init() throws ServletException {
		if (emf == null) {
			emf = Persistence.createEntityManagerFactory("student");
		}
	}

	@SuppressWarnings("unchecked")
	public void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {

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

		if ("list".equals(action)) {

			EntityManager em = emf.createEntityManager();

			try {
				// 读取数据库时不需要事务，直接查询即可
				Query query = em.createQuery(" from ClassEO order by id asc ");

				List<ClassEO> classList = query.getResultList();

				request.setAttribute("classList", classList);
				request.getRequestDispatcher("/listClass.jsp").forward(request,
						response);
			} finally {
				em.close();
			}
		} else if ("add".equals(action)) {

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

			// 如果没有输入名称，则抛出StudentException异常。
			if (name == null || name.trim().length() == 0) {
				throw new StudentException("请填写班级名称");
			}

			// 获取EntityManager对象
			EntityManager em = emf.createEntityManager();

			// JPA写数据库必须开启事务。
			EntityTransaction trans = em.getTransaction();

			try {
				// 事务开始
				trans.begin();

				// 查找同名的ClassEO
				List classList = em.createQuery(
						" from ClassEO where name = :name  ").setParameter(
						"name", name).getResultList();

				// 如果已经存在，则报错
				if (classList.size() > 0) {
					throw new StudentException("班级已经存在：" + name);
				}

				// new一个新的Entity Object
				ClassEO classEO = new ClassEO();

				// 设置名称。ID有数据库自动生成。
				classEO.setName(name);

				// persist
				em.persist(classEO);

				// 事务提交。如果前面或者这时有异常抛出，会自动回滚（Rollback）。
				trans.commit();

				// 成功信息
				request.setAttribute("msg", "班级 " + classEO.getName()
						+ " 添加成功。");

				// 显示成功页面
				request.setAttribute("classEO", classEO);
				request.getRequestDispatcher("/addClassSuccess.jsp").forward(
						request, response);

			} finally {
				// EntityManager 对象关闭
				em.close();
			}

		} else if ("edit".equals(action)) {

			EntityManager em = emf.createEntityManager();

			try {
				// 要修改的班级ID
				int classId = Integer.parseInt(request.getParameter("classId"));

				// 查找班级实体
				ClassEO classEO = em.find(ClassEO.class, classId);

				request.setAttribute("classEO", classEO);

				request.getRequestDispatcher("/addClass.jsp").forward(request,
						response);

			} finally {
				em.close();
			}
		} else if ("save".equals(action)) {

			EntityManager em = emf.createEntityManager();

			// 写数据库，需要事务
			EntityTransaction trans = em.getTransaction();

			try {
				// 事务开始
				trans.begin();

				// 修改的是哪个班级
				int classId = Integer.parseInt(request.getParameter("classId"));

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

				if (name == null || name.trim().length() == 0) {
					throw new StudentException("请填写班级名称");
				}

				List list = em.createQuery(
						" from ClassEO where name = :name and id <> :id ")
						.setParameter("name", name).setParameter("id", classId)
						.getResultList();

				if (list.size() > 0) {
					throw new StudentException("修改后的班级名称与其他班级冲突，修改失败");
				}

				// 查找班级实体
				ClassEO classEO = em.find(ClassEO.class, classId);

				// 修改属性
				classEO.setName(name);

				em.merge(classEO);

				trans.commit();

				request.setAttribute("msg", "班级 " + classEO.getName()
						+ " 修改成功。");

				request.setAttribute("classEO", classEO);
				request.getRequestDispatcher("/addClassSuccess.jsp").forward(
						request, response);
			} finally {
				em.close();
			}

		} else if ("delete".equals(action)) {

			EntityManager em = emf.createEntityManager();

			EntityTransaction trans = em.getTransaction();

			try {

				trans.begin();

				int classId = Integer.parseInt(request.getParameter("classId"));

				ClassEO classEO = em.find(ClassEO.class, classId);

				if (classEO.getStudents().size() > 0) {
					throw new StudentException("班级 " + classEO.getName()
							+ " 还有 " + classEO.getStudents().size()
							+ " 个学生，不能删除。");
				}

				em.remove(classEO);

				trans.commit();

				request.setAttribute("msg", "班级 " + classEO.getName()
						+ " 删除成功。");

				request.setAttribute("classEO", classEO);
				request.getRequestDispatcher("/addClassSuccess.jsp").forward(
						request, response);

			} finally {
				em.close();
			}
		}

	}

	public void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {

		this.doGet(request, response);
	}

	@Override
	public void destroy() {
		// 销毁 EntityManagerFactory
		emf.close();
	}

}