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Tolgar

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How to read data from a mysql database in Java?

Hi,
I use the following code to read data from a database:

    public List<HashMap<Integer, String>> getFullCheckList() throws ClassNotFoundException, SQLException{
        Class.forName("com.mysql.jdbc.Driver") ;
        Connection conn = DriverManager.getConnection("jdbc:mysql://servername/database", "database", "pwd") ;
        Statement stmt = conn.createStatement() ;
        String querycheckName = "SELECT `name` and `id` FROM `check`;" ;
        ResultSet rs = stmt.executeQuery(querycheckName) ;
        ArrayList<HashMap<Integer, String>> checkList = new ArrayList<HashMap<Integer, String>>();
        while(rs.next()) {
            System.out.println("rs:" + rs);
            HashMap<Integer, String> check = new HashMap<Integer, String>();
            System.out.println("rs.getInt(1): " + rs.getInt(1));
            System.out.println("rs.getString(1): " + rs.getString(1));
            check.put(rs.getInt(1), rs.getString(1));
            System.out.println("check:" + rs);
            checkList.add(check);
        }
        rs.close();
        stmt.close();
        conn.close();
        System.out.println("checkList:" + checkList);
        return checkList;
    }

Open in new window


However, with this code when I print checkList in line 17, I only see the following:
checkList:[{0=0}, {0=0}, {0=0}, {0=0}, {0=0}, {0=0}, {0=0}, {0=0}, {0=0}, {0=0}, {0=0}, {0=0}, {0=0}, {0=0}, {0=0}, {0=0}, {0=0}, {0=0}, {0=0}, {0=0}, {0=0}, {0=0}, {0=0}, {0=0}, {0=0}, {0=0}, {0=0}, {0=0}, {0=0}, {0=0}, {0=0}, {0=0}, {0=0}, {0=0}, {0=0}, {0=0}]
[{0=0}, {0=0}, {0=0}, {0=0}, {0=0}, {0=0}, {0=0}, {0=0}, {0=0}, {0=0}, {0=0}, {0=0}, {0=0}, {0=0}, {0=0}, {0=0}, {0=0}, {0=0}, {0=0}, {0=0}, {0=0}, {0=0}, {0=0}, {0=0}, {0=0}, {0=0}, {0=0}, {0=0}, {0=0}, {0=0}, {0=0}, {0=0}, {0=0}, {0=0}, {0=0}, {0=0}]

Open in new window


When I print rs, check, rs.getInt(1) and  rs.getString(1) in lines 9, 11, 12 and 14, I get this:

rs: com.mysql.jdbc.JDBC4ResultSet@7cf1bb78
rs.getInt(1): 0
rs.getString(1): 0
check: com.mysql.jdbc.JDBC4ResultSet@7cf1bb78
rs: com.mysql.jdbc.JDBC4ResultSet@7cf1bb78
rs.getInt(1): 0
rs.getString(1): 0
check: com.mysql.jdbc.JDBC4ResultSet@7cf1bb78
rs: com.mysql.jdbc.JDBC4ResultSet@7cf1bb78
rs.getInt(1): 0
rs.getString(1): 0
check: com.mysql.jdbc.JDBC4ResultSet@7cf1bb78
rs: com.mysql.jdbc.JDBC4ResultSet@7cf1bb78
rs.getInt(1): 0
rs.getString(1): 0
check: com.mysql.jdbc.JDBC4ResultSet@7cf1bb78
rs: com.mysql.jdbc.JDBC4ResultSet@7cf1bb78
rs.getInt(1): 0
rs.getString(1): 0
check: com.mysql.jdbc.JDBC4ResultSet@7cf1bb78
rs: com.mysql.jdbc.JDBC4ResultSet@7cf1bb78
rs.getInt(1): 0
rs.getString(1): 0
check: com.mysql.jdbc.JDBC4ResultSet@7cf1bb78
rs: com.mysql.jdbc.JDBC4ResultSet@7cf1bb78
rs.getInt(1): 0
rs.getString(1): 0
check: com.mysql.jdbc.JDBC4ResultSet@7cf1bb78
rs: com.mysql.jdbc.JDBC4ResultSet@7cf1bb78
rs.getInt(1): 0
rs.getString(1): 0
check: com.mysql.jdbc.JDBC4ResultSet@7cf1bb78
rs: com.mysql.jdbc.JDBC4ResultSet@7cf1bb78
rs.getInt(1): 0
rs.getString(1): 0
check: com.mysql.jdbc.JDBC4ResultSet@7cf1bb78
rs: com.mysql.jdbc.JDBC4ResultSet@7cf1bb78
rs.getInt(1): 0
rs.getString(1): 0
check: com.mysql.jdbc.JDBC4ResultSet@7cf1bb78
rs: com.mysql.jdbc.JDBC4ResultSet@7cf1bb78
rs.getInt(1): 0
rs.getString(1): 0
check: com.mysql.jdbc.JDBC4ResultSet@7cf1bb78
rs: com.mysql.jdbc.JDBC4ResultSet@7cf1bb78
rs.getInt(1): 0
rs.getString(1): 0
check: com.mysql.jdbc.JDBC4ResultSet@7cf1bb78
rs: com.mysql.jdbc.JDBC4ResultSet@7cf1bb78
rs.getInt(1): 0
rs.getString(1): 0
check: com.mysql.jdbc.JDBC4ResultSet@7cf1bb78
rs: com.mysql.jdbc.JDBC4ResultSet@7cf1bb78
rs.getInt(1): 0
rs.getString(1): 0
check: com.mysql.jdbc.JDBC4ResultSet@7cf1bb78
rs: com.mysql.jdbc.JDBC4ResultSet@7cf1bb78
rs.getInt(1): 0
rs.getString(1): 0
check: com.mysql.jdbc.JDBC4ResultSet@7cf1bb78
rs: com.mysql.jdbc.JDBC4ResultSet@7cf1bb78
rs.getInt(1): 0
rs.getString(1): 0
check: com.mysql.jdbc.JDBC4ResultSet@7cf1bb78
rs: com.mysql.jdbc.JDBC4ResultSet@7cf1bb78
rs.getInt(1): 0
rs.getString(1): 0
check: com.mysql.jdbc.JDBC4ResultSet@7cf1bb78
rs: com.mysql.jdbc.JDBC4ResultSet@7cf1bb78
rs.getInt(1): 0
rs.getString(1): 0
check: com.mysql.jdbc.JDBC4ResultSet@7cf1bb78
rs: com.mysql.jdbc.JDBC4ResultSet@7cf1bb78
rs.getInt(1): 0
rs.getString(1): 0
check: com.mysql.jdbc.JDBC4ResultSet@7cf1bb78
rs: com.mysql.jdbc.JDBC4ResultSet@7cf1bb78
rs.getInt(1): 0
rs.getString(1): 0
check: com.mysql.jdbc.JDBC4ResultSet@7cf1bb78
rs: com.mysql.jdbc.JDBC4ResultSet@7cf1bb78
rs.getInt(1): 0
rs.getString(1): 0
check: com.mysql.jdbc.JDBC4ResultSet@7cf1bb78
rs: com.mysql.jdbc.JDBC4ResultSet@7cf1bb78
rs.getInt(1): 0
rs.getString(1): 0
check: com.mysql.jdbc.JDBC4ResultSet@7cf1bb78
rs: com.mysql.jdbc.JDBC4ResultSet@7cf1bb78
rs.getInt(1): 0
rs.getString(1): 0
check: com.mysql.jdbc.JDBC4ResultSet@7cf1bb78
rs: com.mysql.jdbc.JDBC4ResultSet@7cf1bb78
rs.getInt(1): 0
rs.getString(1): 0
check: com.mysql.jdbc.JDBC4ResultSet@7cf1bb78
rs: com.mysql.jdbc.JDBC4ResultSet@7cf1bb78
rs.getInt(1): 0
rs.getString(1): 0
check: com.mysql.jdbc.JDBC4ResultSet@7cf1bb78
rs: com.mysql.jdbc.JDBC4ResultSet@7cf1bb78
rs.getInt(1): 0
rs.getString(1): 0
check: com.mysql.jdbc.JDBC4ResultSet@7cf1bb78
rs: com.mysql.jdbc.JDBC4ResultSet@7cf1bb78
rs.getInt(1): 0
rs.getString(1): 0
check: com.mysql.jdbc.JDBC4ResultSet@7cf1bb78
rs: com.mysql.jdbc.JDBC4ResultSet@7cf1bb78
rs.getInt(1): 0
rs.getString(1): 0
check: com.mysql.jdbc.JDBC4ResultSet@7cf1bb78
rs: com.mysql.jdbc.JDBC4ResultSet@7cf1bb78
rs.getInt(1): 0
rs.getString(1): 0
check: com.mysql.jdbc.JDBC4ResultSet@7cf1bb78
rs: com.mysql.jdbc.JDBC4ResultSet@7cf1bb78
rs.getInt(1): 0
rs.getString(1): 0
check: com.mysql.jdbc.JDBC4ResultSet@7cf1bb78
rs: com.mysql.jdbc.JDBC4ResultSet@7cf1bb78
rs.getInt(1): 0
rs.getString(1): 0
check: com.mysql.jdbc.JDBC4ResultSet@7cf1bb78
rs: com.mysql.jdbc.JDBC4ResultSet@7cf1bb78
rs.getInt(1): 0
rs.getString(1): 0
check: com.mysql.jdbc.JDBC4ResultSet@7cf1bb78
rs: com.mysql.jdbc.JDBC4ResultSet@7cf1bb78
rs.getInt(1): 0
rs.getString(1): 0
check: com.mysql.jdbc.JDBC4ResultSet@7cf1bb78
rs: com.mysql.jdbc.JDBC4ResultSet@7cf1bb78
rs.getInt(1): 0
rs.getString(1): 0
check: com.mysql.jdbc.JDBC4ResultSet@7cf1bb78
rs: com.mysql.jdbc.JDBC4ResultSet@7cf1bb78
rs.getInt(1): 0
rs.getString(1): 0
check: com.mysql.jdbc.JDBC4ResultSet@7cf1bb78
rs: com.mysql.jdbc.JDBC4ResultSet@7cf1bb78
rs.getInt(1): 0
rs.getString(1): 0
check: com.mysql.jdbc.JDBC4ResultSet@7cf1bb78

Open in new window


Why can't I read the "name" column from the "check" table in this database? Any ideas?

Thanks,
Java
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CEHJ
SOLUTION
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CEHJ
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CEHJ
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Among other things, you cannot retrieve the same value from the resultset twice.
What makes you say that?
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CEHJ
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??
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mrcoffee365
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CEHJ -- feel free to try it.  Once a column in a row in the resultset is retrieved with getString (or whatever) then you can't get it again with getString for that row.
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Tolgar

ASKER

@CEHJ: So how should it be then?
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mrcoffee365
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Tolgar:  if you're interested in fixing your code, try the sample I posted.
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Tolgar

ASKER

It is all set. Thanks!

And I  would appreciate if you can take a look at this post:

https://www.experts-exchange.com/questions/28230910/Null-pointer-exception-in-unselecting-checkbox-in-Java.html

Thanks,
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CEHJ
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CEHJ -- feel free to try it.
I just did, with the following minor alteration to some existing code, with no difficulty whatever:

	    while(rs.next()) {
		//System.out.println(rs.getString(1));
		System.out.printf("%s\t%s%n", rs.getString(1), rs.getString(1));
	    }

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@CEHJ: So how should it be then?
Well, my answer was quite specific about the (only) problems with your code
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Tolgar

ASKER

ok. I am ending this post. Thanks a lot.

Can you please take a look at this question? I am struggling with it.

https://www.experts-exchange.com/questions/28230910/Null-pointer-exception-in-unselecting-checkbox-in-Java.html?anchorAnswerId=39465367#a39465367
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CEHJ
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Can you please take a look at this question?
Sorry - i don't do SWT
Java
Java

Java is a platform-independent, object-oriented programming language and run-time environment, designed to have as few implementation dependencies as possible such that developers can write one set of code across all platforms using libraries. Most devices will not run Java natively, and require a run-time component to be installed in order to execute a Java program.

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