如何在数据库连接中正确使用try-with-resources? [英] How to properly use try-with-resources in Database connection?

问题描述

我环顾四周，但似乎找不到我的问题的答案.

I have looked around, but can't seem to find the answer to my question.

这是上下文:我必须连接到Java程序中的数据库，并执行一个我无法控制且事先不知道的SQL请求.为此，我使用下面的代码.

Here is the context : I have to connect to a Database in my Java program and execute a SQL request that I have no control over and don't know in advance. To do that I use the code below.

public Collection<HashMap<String, String>> runQuery(String request, int maxRows) {

    List<HashMap<String, String>> resultList = new ArrayList<>();

    DataSource datasource = null;

    try {

        Context initContext = new InitialContext();
        datasource = (DataSource) initContext.lookup("java:jboss/datasources/xxxxDS"); 

    } catch (NamingException ex) {

        // throw something.
    }

    try (Connection conn = datasource.getConnection();
         Statement statement = conn.createStatement();
         ResultSet rs = statement.executeQuery(request); ) {

        while (rs.next()) 
        {
            HashMap<String, String> map = new HashMap<>();

            for (int i = 1; i <= rs.getMetaData().getColumnCount(); i++) {
                map.put(rs.getMetaData().getColumnName(i).toUpperCase(), rs.getString(i));
            }

            resultList.add(map);             
        }

    } catch (SQLException ex) {

        // throw something.
    }

    return resultList;       
}

我面临的问题是:如您所见，还有另一个我不使用的参数maxRows.我需要将其指定给statement，但不能在try-with-resources中执行.

The issue I am facing is : As you can see there is another parameter maxRows that I don't use. I need to specify this to the statement but can't do it in the try-with-resources.

我想通过在第一个内部嵌套另一个try-with-resources以便指定最大行数来避免这种方法的认知复杂性(例如在此代码示例中).

I would like to avoid increasing cognitive complexity of this method by nesting another try-with-resources inside the first one in order to specify the max number of rows (like in this sample of code).

try (Connection conn = datasource.getConnection();
 Statement statement = conn.createStatement(); ) {

    statement.setMaxRows(maxRows);

    try (ResultSet rs = statement.executeQuery(request); ) {

        while (rs.next()) 
        {
            HashMap<String, String> map = new HashMap<>();

            for (int i = 1; i <= rs.getMetaData().getColumnCount(); i++) {
                map.put(rs.getMetaData().getColumnName(i).toUpperCase(), rs.getString(i));
            }

            resultList.add(map);             
        }
    }

} catch (SQLException ex) {

    // throw something.
}

有什么办法可以只用一个try-with-resources吗?

Is there any way to do it with only one try-with-resources?

推荐答案

如果您可以选择其他方法，那么仅需使用一个try-resources即可.

If you are fine to go for an additional method then it can be possible with only one try-resources

代替Statement statement = conn.createStatement();

Statement statement = createStatement(conn, maxRows);

在该新方法中，创建Statement对象并设置maxRows并返回语句obj.

Inside that new method, create Statement object and set the maxRows and return the statement obj.

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