添加到地图时的Java异常

Question

Not sure what is wrong...it should work or maybe am missing something? the following is the code:

public class TestOracleMap implements java.io.Serializable{
static TreeMap<String, Integer> map;
static TreeMap<String, Integer> localMap = new TreeMap<String, Integer>();

public static void StoreMapInDB(TreeMap<String, Integer> map) throws
        IOException, FileNotFoundException{
    try {
  PreparedStatement insertMap = null;
  //String insertString = "INSERT INTO TESTMAP(ID, MPFIELD) VALUES (1, ?)";
  Connection con=null;
  con.setAutoCommit(false);
  Class.forName("oracle.jdbc.driver.OracleDriver");
  con=DriverManager.getConnection(
    "jdbc:oracle:thin:@oXXX",
    "XXX",
    "XXX");

  ByteArrayOutputStream bos = new ByteArrayOutputStream() ;
  ObjectOutputStream out = new ObjectOutputStream(bos);
  out = new ObjectOutputStream(bos) ;
  out.writeObject(map);
  out.close();

  byte[] buf = bos.toByteArray();
  PreparedStatement prepareStatement = con.prepareStatement("insert into  

  TESTMAP(ID,MAPFIELD)values(?,?)");
  prepareStatement.setLong(1, 1);
  prepareStatement.setBinaryStream(2, new ByteArrayInputStream(buf), buf.length);



 // insertMap.executeUpdate();
  con.commit();
    } catch(Exception e){e.printStackTrace();}
}

public static void main(String[] args)
{
    try{
    DateTime today = new DateTime();
    int x = 1;
    map.put("Hello!", x);
    StoreMapInDB(map);
    }catch(IOException ioe){
        System.err.print(ioe);
    }
}
}

the error is in the line in the main method that is:

map.put("Hello!", x);

it gives:

Exception in thread "main" java.lang.NullPointerException
at core.smd.classes.TestOracleMap.main(TestOracleMap.java:61)
 Java Result: 1

Answer 1

Seems like you never instantiate map . You declare it here

static TreeMap<String, Integer> map;

but when you use it here it is still null giving you the NullPointerException .

map.put("Hello!", x);

If you do this before

map = new TreeMap<String, Integer>();

it should run fine.

Answer 2

Where did you initialize "map"? Looks null to me.

Change this line:

static TreeMap<String, Integer> map = new TreeMap<String, Integer>();

You declare this and set it to null, but I don't see where you use it.

PreparedStatement insertMap = null;

You've got more heartache ahead here:

Connection con=null;
  Class.forName("oracle.jdbc.driver.OracleDriver");
  con=DriverManager.getConnection(
    "jdbc:oracle:thin:@oXXX",
    "XXX",
    "XXX");
  con.setAutoCommit(false);

Move the autoCommit down until after you get the connection from the driver manager.

You're serializing the Map to INSERT it into the database? That's not normalized. A normalized schema would have a row per entry.

The more I read your code, the less sense it makes. Good luck.

Answer 3

You never initialize map to anything, hence it is null . You'll need to assign a valid TreeMap<String, Integer> to it somewhere, like for instance on line 2 when you declare it, use:

static TreeMap<String, Integer> map = new TreeMap<String, Integer>();

Answer 4

变量映射永远不会初始化，仅在构造函数中声明。

map = new TreeMap<String, Integer>();

Answer 5

您只声明地图，而不初始化它

static TreeMap<String, Integer> map=new HashMap<String,Integer>();

Answer 6

static TreeMap<String, Integer> map = new TreeMap<String, Integer>(); // <-- in your code, you're not constructing it
static TreeMap<String, Integer> localMap = new TreeMap<String, Integer>();

Answer 7

You r initializing a variable Connection con = null; then ur setting con.setAutoCommit(false).. Without creating object for that how can u set auto commit for that?

Answer 8

您确实在声明时初始化了map对象，就像您在声明时初始化了localMap对象一样，只是检查了