[英]How can I use map.KeySet() in sql query in java
我有一个LinkedHahMap map1,它的键是我的beam_current ,它是双精度类型,值是我的logtime,它是字符串类型。 现在,我想在我的SQL查询中使用此map1.keySet()-
Set<Double> arr= map1.keySet();
String vs2="select b.beam_current, b.beam_energy where
b.logtime between '"+first+"' and '"+last+"' and b.beam_current in('"+arr+"')";
但是当我使用保存map1 key值的 arr时,**什么都没有显示。**我们不能在sql查询中使用map1.KeySet()方法吗?还是以错误的方式暗示了它?
首先将地图键转换为逗号分隔的字符串,然后在查询中使用它。
List<Double> slist = new ArrayList<Double>(map1.keySet());
String s = StringUtils.join(slist, ',');
String vs2="select b.beam_current, b.beam_energy where
b.logtime between '"+first+"' and '"+last+"' and
b.beam_current in('"+s+"')";
如果您不想依赖外部库(例如StringUtils.join),则可以手动执行:
public static void main(String[] args) {
HashMap<Double, String> map1 = new HashMap<Double, String>();
map1.put(1.5, "");
map1.put(2.5, "");
String first = "first";
String last = "last";
String query = buildQuery(map1, first, last);
System.out.println(query);
}
private static String buildQuery(HashMap<Double, String> map1, String first, String last) {
StringBuilder sb = new StringBuilder();
sb.append("select b.beam_current, b.beam_energy where b.logtime between '");
sb.append(first);
sb.append("' and '");
sb.append(last);
sb.append("' and b.beam_current in (");
String separator = "";
for (Double val : map1.keySet()) {
sb.append(separator);
sb.append(val);
separator = ", ";
}
sb.append(")");
return sb.toString();
}
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