JDBC SQLIte搜索中的空指針異常

Question

我已經找到了一種搜索SQLite數據庫並顯示與傳入的字符串值匹配的行的方法。問題是我遇到了nullPointerException ，我也不知道為什么，因為據我所知，這沒有問題。 代碼如下：

public static void search(String search)
      {
          String [] entries = new String[6]; 
        Connection c = null;
        Statement stmt = null;
        try {
          Class.forName("org.sqlite.JDBC");
          c = DriverManager.getConnection("jdbc:sqlite:WalkerTechCars.db");
          c.setAutoCommit(false);
          System.out.println("Opened database successfully");

          stmt = c.createStatement();
          ResultSet rs = stmt.executeQuery( "SELECT * FROM CUSTOMERS;" );
          while ( rs.next() ) {
             int phone = rs.getInt("phone");
             String  surname = rs.getString("surname");
             String  firstname = rs.getString("firstname");
             int home  = rs.getInt("home");
             String  address = rs.getString("address");
             String  postcode = rs.getString("postcode");

             if(search.matches(Integer.toString(phone)) || search.matches(surname) || search.matches(firstname) || search.matches(Integer.toString(home)) || search.matches(address) || search.matches(postcode) )
                 {
             System.out.println( "PHONE = " + phone );
             System.out.println( "SURNAME = " + surname );
             System.out.println( "FIRSTNAME = " + firstname );
             System.out.println( "HOME = " + home );
             System.out.println( "ADDRESS = " + address );
             System.out.println( "POSTCODE = " + postcode );
             System.out.println();
             }
          }
          rs.close();
          stmt.close();
          c.close();
        } catch ( Exception e ) {
          System.err.println( e.getClass().getName() + ": " + e.getMessage() );
          System.exit(0);
        }
        System.out.println("Operation done successfully");

      }

問題在於語句

if( .......  || search.matches(postcode) )

如果刪除此語句，則一切運行良好，但是此語句沒有任何問題，因為該字符串已經聲明並且不為null。

Answer 1

您的postcode可能為空。

嘗試編寫如下內容：

if( .......  || (postcode != null && search.matches(postcode)) )

當然，問題可能出在每個參數上，因此您必須為每個人都做，或者以更好的方式思考。

Answer 2

首先嘗試檢查代碼中的搜索參數是否為null，以備將來保存，因為在所有情況下都使用search.matches。 以后可能會發生這種情況，以后您可以將搜索發送為null。 對於郵政編碼，您可以嘗試檢查null，例如（postcode！= null && search.matches（postcode））

if(search!=null)
{
  if(search.matches(Integer.toString(phone)) || search.matches(surname) || search.matches(firstname) || search.matches(Integer.toString(home)) || search.matches(address) || (postcode!=null && search.matches(postcode)) )
                 {
             System.out.println( "PHONE = " + phone );
             System.out.println( "SURNAME = " + surname );
             System.out.println( "FIRSTNAME = " + firstname );
             System.out.println( "HOME = " + home );
             System.out.println( "ADDRESS = " + address );
             System.out.println( "POSTCODE = " + postcode );
             System.out.println();
             }

}