pstmt=con.prepareStatement(sql); java.lang.NullPointerException
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public class Util {
private Connection con;
private PreparedStatement pstmt;
private String sql;
private Dao dao;
private Statement stmt;
public Util() {
try {
Class.forName("com.mysql.jdbc.Driver");
Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/account", "root", "123456");//此处!!!!!!!!!!!!
System.out.println("connection");
// pstmt = con.prepareStatement("select * from user");
// ResultSet rs = pstmt.executeQuery();
// while(rs.next()){
// System.out.println("id:"+rs.getInt("id")+",username:"+rs.getString("username")+",age:"+rs.getString("age"));
// }
} catch (Exception e) {
e.printStackTrace();
}
}
public void setSql(String sql) {
this.sql = sql;
System.out.println(this.sql);
// try {
// pstmt = con.prepareStatement(sql);
// } catch (Exception e) {
// e.printStackTrace();
// }
}
public ResultSet query() {
ResultSet rs = null;
if (sql == null) {
System.out.println("查询语句为空!请检查");
} else{
try {
System.out.println(sql+con);
pstmt=con.prepareStatement(sql);
rs = pstmt.executeQuery();
//rs = pstmt.executeQuery();
} catch (SQLException e) {
e.printStackTrace();
}
}
return rs;
private Connection con;
private PreparedStatement pstmt;
private String sql;
private Dao dao;
private Statement stmt;
public Util() {
try {
Class.forName("com.mysql.jdbc.Driver");
Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/account", "root", "123456");//此处!!!!!!!!!!!!
System.out.println("connection");
// pstmt = con.prepareStatement("select * from user");
// ResultSet rs = pstmt.executeQuery();
// while(rs.next()){
// System.out.println("id:"+rs.getInt("id")+",username:"+rs.getString("username")+",age:"+rs.getString("age"));
// }
} catch (Exception e) {
e.printStackTrace();
}
}
public void setSql(String sql) {
this.sql = sql;
System.out.println(this.sql);
// try {
// pstmt = con.prepareStatement(sql);
// } catch (Exception e) {
// e.printStackTrace();
// }
}
public ResultSet query() {
ResultSet rs = null;
if (sql == null) {
System.out.println("查询语句为空!请检查");
} else{
try {
System.out.println(sql+con);
pstmt=con.prepareStatement(sql);
rs = pstmt.executeQuery();
//rs = pstmt.executeQuery();
} catch (SQLException e) {
e.printStackTrace();
}
}
return rs;
}
包装util类时报错,发现在在构造方法中重新声明了Connection con导致传con失败为空!!
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