Chapter 5. Using Cursors
Prev |  | Next

## Chapter 5. Using Cursors

Cursors provide a mechanism by which you can iterate over the records in a database. Using cursors, you can get, put, and delete database records. If a database allows duplicate records, then cursors are the only mechanism by which you can access anything other than the first duplicate for a given key.

This chapter introduces cursors. It explains how to open and close them, how to use them to modify databases, and how to use them with duplicate records.

## Opening and Closing Cursors

To use a cursor, you must open it using the `Database.openCursor()` method. When you open a cursor, you can optionally pass it a `CursorConfig` object to set cursor properties. Currently, the only available property tells the cursor to perform dirty reads. (For a description of dirty reads, see Configuring Dirty Reads).

For example:

    package com.sleepycat.examples.je.gettingStarted;

    import com.sleepycat.je.Cursor;
    import com.sleepycat.je.CursorConfig;
    import com.sleepycat.je.Database;
    import com.sleepycat.je.DatabaseException;
    import com.sleepycat.je.Environment;

    import java.io.File;

    ...
    Environment myDbEnvironment = null;
    Database myDatabase = null;
    Cursor myCursor = null;

    try {
        myDbEnvironment = new Environment(new File("/export/dbEnv"), null);
        myDatabase = myDbEnvironment.openDatabase(null, "myDB", null);

        myCursor = myDatabase.openCursor(null, null);
    } catch (DatabaseException dbe) {
        // Exception handling goes here ...
    }

To close the cursor, call the `Cursor.close()` method. Note that if you close a database that has cursors open in it, then it will throw an exception and close any open cursors for you. For best results, close your cursors from within a `finally` block.

    package com.sleepycat.examples.je.gettingStarted;

    import com.sleepycat.je.Cursor;
    import com.sleepycat.je.Database;
    import com.sleepycat.je.Environment;

    ...
    try {
        ...
    } catch ... {
    } finally {
        try {
            if (myCursor != null) {
                myCursor.close();
            }

            if (myDatabase != null) {
                myDatabase.close();
            }

            if (myDbEnvironment != null) {
                myDbEnvironment.close();
            }
        } catch(DatabaseException dbe) {
            System.err.println("Error in close: " + dbe.toString());
        }
    }

Prev | Up | Next
Database Record Example | Home | Getting Records Using the Cursor