新手尝试使用Java ArrayList 存储从数据库获取的ResultSet [英] newbie attempt to use Java ArrayList to store ResultSet obtained from database

问题描述

我有一个使用 JDBC 与 Java 应用程序服务器通信的数据库服务器.我想将数据库 ResultSet 中的数据存储到 Java 变量中.

I have a database server communicating with a Java application server using JDBC. I want to store data from the database ResultSet into Java variables.

这是我的 Java 课程 HRPeople:

Here's my Java class, HRPeople:

public class HRPeople {
    public int elements;
    public String[] FirstName;
    public String[] LastName;
    public String[] Email;
    public int[] Salary;
}

我目前使用这个类来存储来自 ResultSet 的数据，如下:

I currently use this class to store data from ResultSet, as follows:

query = "SELECT first_name, last_name, email, salary FROM HR.Employees where rownum < 6";
rset = stmt.executeQuery(query);
while (rset.next()) {
    returnHRdata.FirstName[ii] = rset.getString("first_name");
    returnHRdata.LastName[ii]  = rset.getString("last_name");
    returnHRdata.Email[ii]     = rset.getString("email");
    returnHRdata.Salary[ii]    = rset.getInt("salary");
    ii = ii + 1;
}

上述场景的问题在于原始数组要求我知道 ResultSet 中的行数，以便我可以正确初始化这些数组.所以我想要做的是使用 ArrayList 代替.我将如何修改上述场景来做到这一点?

The problem with the above scenario is that the primitive arrays require me to know the number of rows in the ResultSet so that I can properly initialize those arrays. So what I want to do is use an ArrayList instead. How would I modify the above scenario to do this?

这是我的初步尝试(是否接近)?上面显示的 HRPeople.java 文件是否在这种情况下使用过?

Here's my initial attempt (is this close)? Is HRPeople.java file shown above even used in this scenario?

query = "SELECT first_name, last_name, email, salary FROM HR.Employees where rownum < 6";
rset = stmt.executeQuery(query);
List<HRPeople> returnHRdata = new ArrayList<HRPeople>();
while (rset.next()) {
   returnHRdata.FirstName = rset.getString("first_name");
   returnHRdata.LastName  = rset.getString("last_name");
   returnHRdata.Email     = rset.getString("email");
   returnHRdata.Salary    = rset.getInt("salary");
   returnHRdata.add;
}

更新 1:

如果我在代码中添加以下内容，

If I add to the code the following,

return returnHRdata;

我收到以下错误(知道为什么吗?):

I get the following error (any idea why?):

myClass.java:213: incompatible types
found   : java.util.List<HRPerson>
required: java.util.ArrayList<HRPerson>
    return returnHRdata;
           ^
1 error

推荐答案

您可能希望首先像这样定义一个 HRPerson:

You probably want to first define an HRPerson like this:

public class HRPerson {
    public String firstName;
    public String lastName;
    public String email;
    public int salary;
}

然后你的主要代码看起来像:

Then your main code would look like:

query = "SELECT first_name, last_name, email, salary FROM HR.Employees where rownum < 6";
rset = stmt.executeQuery(query);
List<HRPerson> returnHRdata = new ArrayList<HRPerson>();
while (rset.next()) {
   HRPerson person = new HRPerson();
   person.firstName = rset.getString("first_name");
   person.lastName  = rset.getString("last_name");
   person.email     = rset.getString("email");
   person.salary    = rset.getInt("salary");
   returnHRdata.add(person);
}

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