Question

我已经参与了一段时间，尝试了不同的例子（包括我在这里找到的一些例子），并试图让它们适应我的需要。

我正在尝试在servlet中使用数据库查询来填充生成的结果html表单中的组合框。当它全部编译并且页面弹出一个组合框时，框中没有任何内容可供选择，这告诉我传递变量的方式有问题。

我基本上将我的方法缩小到两个，但两者都得到了相同的结果有人可以看看并给我一个线索吗？

out.print(`"<tr><td>SoldWhich Home ID:  `</td><td>"`);
//Query table for results to go into option box  
ResultSet rs1 = null;  
Statement stmt1 = null;  
Connection con1 = null;  

try {
    Class.forName(DRIVER);  
    con1 = DriverManager.getConnection(URL, username, password);  
    String sql = "SELECT home_id FROM Home";  
    stmt1 = con1.createStatement();  
    rs1 = stmt1.executeQuery(sql);  
    ArrayList<String> soldWhich = new ArrayList<String>();
    List<String> soldWhich = new ArrayList<String>();

    while (rs1.next()){
        for (int i=1;i<=rs1.getRow(); i++ ){
            String value = rs1.getString(1);
            soldWhich.add(value);
        }
    }
}
catch(Exception e){}
//Begin option box
out.print(`"<select width=\"150px\" align=\"right\" name=\"soldWhichBox\">"`);
String soldWhich[] = (String[])req.getAttribute("home_id");
//populate with query output
try{
    for(String sh : soldWhich){
        out.print(`"<option width=\"150px\" align=\"right\" value=\""+sh+"\">"+sh+"</option>"`);
    }
    rs1.close();
    con1.close();
}

catch (Exception e){}
out.print(`"</select>"`);
out.print(`"</td></tr>"`);

另一种方法：

out.print(`"<tr><td>SoldWhich Home ID:  </td><td>"`);
//Query table for results to go into option box  
ResultSet rs1 = null;  
Statement stmt1 = null;  
Connection con1 = null;  
try{  

    Class.forName(DRIVER);  
    con1 = DriverManager.getConnection(URL, username, password);
    String sql = "SELECT home_id FROM Home ORDER BY home_id";
    stmt1 = con1.createStatement();
    rs1 = stmt1.executeQuery(sql);
    List<String> soldWhich = new ArrayList<String>();

    while (rs1.next()){
       soldWhich.add(rs1.getString(1));
    }
}
catch(Exception e){}
//Begin option box
out.print(`"<select width=\"150px\" align=\"right\" name=\"soldWhichBox\">"`);
String soldWhich[] = (String [])req.getAttribute("home_id");
//populate with query output
try{
    for(String sh : soldWhich){
        out.print(`"<option width=\"150px\" align=\"right\" value=\""+sh+"\">"+sh+"</option>"`);
    }
    rs1.close();
    con1.close();
}
catch (Exception e){}
out.print(`"</select>"`);
out.print(`"</td></tr>"`);

Answer 1

我认为你实际上并没有在“for（String sh：soldWhich）”循环中获得值（sh）。你能尝试在简单的表格中打印这些值，看看你是否真的得到了数据吗？另外，为什么你不使用jstl来执行此任务？并且你的catch块不会记录任何错误，以防你实际上遇到一些不被注意的错误。

Answer 2

您在哪里设置“home_id”请求属性，为什么要设置它？我认为您应该删除以下代码行，看看它是否有效。将代码修改为此。

List<String> soldWhich = null;
try {
    Class.forName(DRIVER);  
    con1 = DriverManager.getConnection(URL, username, password);  
    String sql = "SELECT home_id FROM Home";  
    stmt1 = con1.createStatement();  
    rs1 = stmt1.executeQuery(sql);  
    soldWhich = new ArrayList<String>();

    while (rs1.next()){
        for (int i=1;i<=rs1.getRow(); i++ ){
            String value = rs1.getString(1);
            soldWhich.add(value);
        }
    }
}

数据库查询没有填充到组合框...为什么？

2 个答案: