我正在尝试执行一个包含where条件的sql查询。但每当我执行查询时，它都会给我 java.lang.NullPointerException 。请帮助我!
我正在使用 mssql 和 java
dbURL = "jdbc:sqlserver://ip:portnumber;databaseName=abc";
username = "abc";
password = "abc";
//Load MS SQL JDBC Driver
Class.forName("com.microsoft.sqlserver.jdbc.SQLServerDriver");
con = DriverManager.getConnection(dbURL,username,password);
//Creating statement object
st = con.createStatement();
selectquery = "select * from abc where TradeType = '"+tradepair+"'";
rs = st.executeQuery(selectquery);
while (rs.next()) {
getpair = rs.getString("TradeType");
dbTradePair.add(getpair);
}
System.out.println("Pairs :-"+dbTradePair);
当执行“selectquery”时，我得到“java.lang.NullPointerException”。 我希望我能以正确的格式执行 sql 查询。有人可以帮我解决这个问题吗？
最佳答案
像这样(编辑 - 之后正确关闭资源):
//Load MS SQL JDBC Driver
try {
Class.forName("com.microsoft.sqlserver.jdbc.SQLServerDriver");
} catch (ClassNotFoundException e) {
System.out.println(e.getMessage());
}
final String dbURL = "jdbc:sqlserver://ip:portnumber;databaseName=abc";
final String username = "abc";
final String password = "abc";
Connection con = null;
PreparedStatement preparedStatement = null;
final String selectquery = "select * from abc where TradeType = ?";
try {
con = DriverManager.getConnection(dbURL,username,password);
preparedStatement = con.prepareStatement(selectquery);
preparedStatement.setString(1, tradepair);
// execute select SQL stetement
ResultSet rs = preparedStatement.executeQuery();
while (rs.next()) {
String tradeType = rs.getString("TradeType");
System.out.println("tradeType : " + tradeType);
}
} catch (SQLException e) {
System.out.println(e.getMessage());
} finally {
if (preparedStatement != null) {
preparedStatement.close();
}
if (con != null) {
con.close();
}
}
关于java - 如何在java中的where子句中传递变量的值？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/54329540/