jakarta-ee - 如何改善我的DAO？ -Java EE

我想访问我的申请人数据库，这就是为什么我为此创建一个DAO类的原因。

我认为我有很多代码味道，因为我不断重复一些代码。那么，为了减少代码的气味，我该怎么做才能使代码更简单？我违反了什么规则？如何改善我的代码？谢谢。

我的代码如下：

public class ApplicantDAO {

private static ApplicantDAO me = null;

private ApplicantDAO(){};

public static synchronized ApplicantDAO getInstance() {
    if(me == null) {
        me = new ApplicantDAO();
    }
    return me;
}

public Applicant getApplicant(int applicantNumber) throws SQLException {
    Applicant applicant = null;

    Connection conn = null;
    Statement statement= null;
    String query = null;
    ResultSet rs = null;

    try {
        conn = ConnectionManager.getConnection();
        statement = conn.createStatement();
        query = "SELECT * FROM applicant WHERE applicant_no = '" + applicantNumber +"'";    //check applicant_number
        rs = statement.executeQuery(query);

        while(rs.next()){
            applicant = new Applicant();

            applicant.setApplicantNumber(rs.getInt("applicant_no"));
            applicant.setApplicationDate(rs.getString("applicant_date"));
            applicant.setfName(rs.getString("first_name"));
            applicant.setlName(rs.getString("last_name"));
            applicant.setmName(rs.getString("middle_name"));
            applicant.setAge(rs.getInt("age"));
            applicant.setGender(rs.getString("gender"));
            applicant.setEmail(rs.getString("email_address"));
            applicant.setContactNumber(rs.getString("contact_no"));
            applicant.setCity(rs.getString("city"));
            applicant.setSchool(rs.getString("school"));
            applicant.setCourse(rs.getString("course"));
            applicant.setYearGraduated(rs.getInt("year_graduated"));
            applicant.setYearWorkExp(rs.getInt("year_work_exp"));
            applicant.setSourceChannel(rs.getString("source_channel"));
            applicant.setStatus_id(rs.getInt("status_id"));

        }

    } catch (SQLException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }finally {
        if (rs != null) try { rs.close(); } catch (SQLException logOrIgnore) {}
        if (statement != null) try { statement.close(); } catch (SQLException logOrIgnore) {}
        if (conn!= null) try { conn.close(); } catch (SQLException logOrIgnore) {}
    }


    return applicant;
}

public ArrayList<Applicant> getApplicants() throws SQLException{
    ArrayList<Applicant> applicantList = null;
    Applicant applicant = null;

    Connection conn = null;
    Statement statement= null;
    String query = null;
    ResultSet rs = null;

    try {
        conn = ConnectionManager.getConnection();
        statement = conn.createStatement();
        query = "select * from applicant";
        rs = statement.executeQuery(query);

        while(rs.next()){
            if(applicantList == null){
                applicantList = new ArrayList<Applicant>();
            }
            applicant = new Applicant();

            applicant.setApplicantNumber(rs.getInt("applicant_no"));
            applicant.setApplicationDate(rs.getString("applicant_date"));
            applicant.setfName(rs.getString("first_name"));
            applicant.setlName(rs.getString("last_name"));
            applicant.setmName(rs.getString("middle_name"));
            applicant.setAge(rs.getInt("age"));
            applicant.setGender(rs.getString("gender"));
            applicant.setEmail(rs.getString("email_address"));
            applicant.setContactNumber(rs.getString("contact_no"));
            applicant.setCity(rs.getString("city"));
            applicant.setSchool(rs.getString("school"));
            applicant.setCourse(rs.getString("course"));
            applicant.setYearGraduated(rs.getInt("year_graduated"));
            applicant.setYearWorkExp(rs.getInt("year_work_exp"));
            applicant.setSourceChannel(rs.getString("source_channel"));
            applicant.setStatus_id(rs.getInt("status_id"));

            applicantList.add(applicant);
        }

    } catch (SQLException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }finally{
         if (rs != null) try { rs.close(); } catch (SQLException logOrIgnore) {}
         if (statement != null) try { statement.close(); } catch (SQLException logOrIgnore) {}
         if (conn!= null) try { conn.close(); } catch (SQLException logOrIgnore) {}
    }
    return applicantList;
}

最佳答案

我看到的巨大的，明显的问题：


DAO是单例。为什么？
您没有使用EntityManager。还有，为什么呢？


如果您实际上使用的是Java EE（带有问题的标签），而不是J2EE（这是围绕Java 1.4构建的规范），那么DAO模式就完全没有必要了。 EntityManager是新的DAO。

看看The Java EE 6 Tutorial - Persistence的前几节。




我们需要使用J2ee .. :(


好的，所以您仍然需要修复单例实现。考虑到该对象不存储任何内部状态，因此完全没有理由仅创建该对象的一个​​实例。有一个简单的解决方法：


完全删除private static ApplicantDAO me = null;
将getInstance()实现更改为

public static ApplicantDAO getInstance() {
    return new ApplicantDAO();
}

其他气味：


您几乎总是要声明List而不是ArrayList，因此请更改声明，例如

public ArrayList<Applicant> getApplicants() throws SQLException
// to
public List<Applicant> getApplicants() throws SQLException

// and

ArrayList<Applicant> applicantList = null;
// to
List<Applicant> applicantList = null;

关于jakarta-ee - 如何改善我的DAO？ -Java EE，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/6331757/