java 将数据库结果集解析为对象列表
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Parse a Database Result Set into an Object List
提问by chrissygormley
I am trying to get all data from a table contained in a database, and parse it into a List. I have tried a few different techniques and can't get it working. I am trying to serialize the ResultSet so I can send it over a socket. The code I have got so far is:
我试图从包含在数据库中的表中获取所有数据，并将其解析为一个列表。我尝试了几种不同的技术，但无法正常工作。我正在尝试序列化 ResultSet 以便我可以通过套接字发送它。到目前为止我得到的代码是：
public Object readJavaObject(String query, Connection con) throws Exception
{
PreparedStatement stmt = con.prepareStatement(query);
//stmt.setString(1, id);
query_results = stmt.executeQuery();
while (query_results.next())
{
dataObject = query_results.getObject(1);
}
query_results.close();
stmt.close();
return dataObject;
}
public void run()
{
try
{
Class.forName(dbClass);
con = DriverManager.getConnection (dbUrl, user, pass);
query = "SELECT * FROM Bench_table";
dataList = (List) this.readJavaObject(query, con);
con.close();
}
}
I'm not sure what code to write around readJavaObject. Can anyone help to point out where the issue is?
我不确定要写什么代码readJavaObject。谁能帮忙指出问题出在哪里？
Thanks for any help.
谢谢你的帮助。
回答by Bozho
Take a look at DbUtils(from apache-commons).
看看DbUtils（来自 apache-commons）。
If you need a more complex solution for mapping sql results to java objects, take a look at object-relational mapping. In Java the standard is JPA (Java Persistence API), with Hibernate, EclipseLink and OpenJPA as the most famous implementors.
如果您需要更复杂的解决方案来将 sql 结果映射到 java 对象，请查看object-relational mapping。在 Java 中，标准是 JPA（Java Persistence API），其中最著名的实现者是 Hibernate、EclipseLink 和 OpenJPA。
回答by jzd
There are several issues with your code.
您的代码有几个问题。
- You loop through the results but only return data from the last row. Instead create a List in the readJavaObject method and add an element each pass through the loop.
- Instead of getting the item in the first column, I assume you want all the data. You are going to have to be more specific with which "get" methods you use to pull data off the ResultSet. Possibly create a POJO to represent a row of data, then inside the loop populate it and store it in the list.
- Assuming you use a POJO, you might want to use generics with your list to make it easier to get items out of it without having to cast.
- 您遍历结果，但只返回最后一行的数据。而是在 readJavaObject 方法中创建一个 List 并在每次循环时添加一个元素。
- 我假设您需要所有数据，而不是获取第一列中的项目。您将不得不更具体地使用哪些“get”方法从 ResultSet 中提取数据。可能创建一个 POJO 来表示一行数据，然后在循环内填充它并将其存储在列表中。
- 假设您使用 POJO，您可能希望在您的列表中使用泛型，以便更轻松地从列表中获取项目而无需强制转换。
回答by Buhake Sindi
I don't know exactly what you want to achieve, but can I introduce you to the DAO (Data Access Object) Pattern?
我不确切知道您想要实现什么，但我可以向您介绍DAO（数据访问对象）模式吗？
回答by FBB
I recently discovered the CachedRowSet, which does exactly what OP needs. It notablyallows to serialize a ResultSet, and to restore the original when needed.
我最近发现了CachedRowSet，它正是 OP 所需要的。它特别允许序列化 a ResultSet，并在需要时恢复原始文件。
