JDBC

Author: turingfly

Java-8/src/jdbc/ConnectingADataBase.java

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+package jdbc;
+
+import java.sql.*;
+import java.util.HashMap;
+import java.util.Map;
+
+import com.sun.corba.se.pept.transport.Connection;
+
+/**
+ * 
+ * @author chengfeili 
+ * Jun 14, 2017 5:30:14 PM
+ *
+ *         Driver: Knows how to get a connection to the database 
+ *         Connection: Knows how to communicate with the database 
+ *         Statement: Knows how to run the SQL 
+ *         ResultSet: Knows what was returned by a SELECT query
+ * 
+ *         In real applications, you should use a DataSource rather than
+ *         DriverManager to get a Connection. For one thing, there’s no reason
+ *         why you should have to know the database password. It’s far better if
+ *         the database team or another team can set up a data source that you
+ *         can reference. Another reason is that a DataSource maintains a
+ *         connection pool so that you can keep reusing the same connection
+ *         rather than needing to get a new one each time.
+ */
+public class ConnectingADataBase {
+	public void connect() throws SQLException {
+		Connection conn = (Connection) DriverManager.getConnection("jdbc:derby:zoo");
+		System.out.println(conn);
+
+		Connection conn1 = (Connection) DriverManager.getConnection("jdbc:postgresql://localhost:5432/ocp-book",
+				"username", "password");
+		System.out.println(conn1);
+	}
+
+	// Statement: Knows how to run the SQL
+	public void obtainingAStatement() throws SQLException {
+		Connection conn = (Connection) DriverManager.getConnection("jdbc:derby:zoo");
+
+		/**
+		 * Parameters: resultSetType a result set type; one of
+		 * ResultSet.TYPE_FORWARD_ONLY, ResultSet.TYPE_SCROLL_INSENSITIVE, or
+		 * ResultSet.TYPE_SCROLL_SENSITIVE resultSetConcurrency a concurrency
+		 * type; one of ResultSet.CONCUR_READ_ONLY or ResultSet.CONCUR_UPDATABLE
+		 */
+		Statement stmt = ((java.sql.Connection) conn).createStatement(ResultSet.TYPE_FORWARD_ONLY,
+				ResultSet.CONCUR_READ_ONLY);
+
+	}
+
+	public void executingAStatement() throws SQLException {
+		Connection conn = (Connection) DriverManager.getConnection("jdbc:derby:zoo");
+		Statement stmt = ((java.sql.Connection) conn).createStatement();
+		int result = stmt.executeUpdate("insert into species values(10, 'Deer', 3)");
+		System.out.println(result); // 1
+		result = stmt.executeUpdate("update species set name = '' where name = 'None'");
+		System.out.println(result); // 0
+		result = stmt.executeUpdate("delete from species where id =10");
+		System.out.println(result); // 1
+
+		/**
+		 * If sql is a SELECT , the boolean is true and we can get the ResultSet
+		 * . If it is not a SELECT , we can get the number of rows updated.
+		 */
+		boolean isResultSet = stmt.execute("sql");
+		if (isResultSet) {
+			ResultSet rs = stmt.getResultSet();
+			System.out.println("ran a query");
+		} else {
+			int result1 = stmt.getUpdateCount();
+			System.out.println("ran an update");
+		}
+	}
+
+	public void readingAResultSet() throws SQLException {
+		Map<Integer, String> idToNameMap = new HashMap<>();
+		Connection conn = (Connection) DriverManager.getConnection("jdbc:derby:zoo");
+		Statement stmt = ((java.sql.Connection) conn).createStatement();
+		ResultSet rs = stmt.executeQuery("select id, name from species");
+		while (rs.next()) {
+			int id = rs.getInt("id");
+			String name = rs.getString("name");
+			// int id = rs.getInt(1); // first column
+			// String name = rs.getString(2);
+			idToNameMap.put(id, name);
+		}
+		// getObject()
+		while (rs.next()) {
+			Object idField = rs.getObject("id");
+			Object nameField = rs.getObject("name");
+			if (idField instanceof Integer) {
+				int id = (Integer) idField;
+				System.out.println(id);
+			}
+			if (nameField instanceof String) {
+				String name = (String) nameField;
+				System.out.println(name);
+			}
+			System.out.println(idToNameMap); // {1=African Elephant, 2=Zebra}
+		}
+		rs.afterLast();
+		System.out.println(rs.previous()); // last row
+		System.out.println(rs.first());
+		System.out.println(rs.last());
+		System.out.println(rs.absolute(1)); // first row
+		System.out.println(rs.absolute(-1)); // last row
+	}
+
+	// closing a Database
+	public void closingDataBase() throws SQLException {
+		String url = " jdbc:derby:zoo";
+		try (Connection conn = (Connection) DriverManager.getConnection(url);
+				Statement stmt = conn.createStatement();
+				ResultSet rs = stmt.executeQuery("select name from animal")) {
+			while (rs.next())
+				System.out.println(rs.getString(1));
+		}
+	}
+
+	// closing a Database prior to Java 7
+	public void closingDataBase1() throws SQLException {
+		String url = "jdbc:derby:zoo";
+		Connection conn = null;
+		Statement stmt = null;
+		ResultSet rs = null;
+		try {
+			conn = (Connection) DriverManager.getConnection(url);
+			stmt = ((java.sql.Connection) conn).createStatement();
+			rs = stmt.executeQuery("select name from animal");
+			while (rs.next())
+				System.out.println(rs.getString(1));
+		} finally
+
+		{
+			closeResultSet(rs);
+			closeStatement(stmt);
+			closeConnection(conn);
+		}
+	}
+
+	private void closeResultSet(ResultSet rs) {
+		try {
+			if (rs != null)
+				rs.close();
+		} catch (SQLException e) {
+		}
+	}
+
+	private void closeStatement(Statement stmt) {
+		try {
+			if (stmt != null)
+				stmt.close();
+		} catch (SQLException e) {
+		}
+	}
+
+	private void closeConnection(Connection conn) {
+		try {
+			if (conn != null)
+				conn.close();
+		} catch (SQLException e) {
+		}
+	}
+
+	public void dealingWithExceptions() {
+		String url = " jdbc:derby:zoo";
+		try (Connection conn = DriverManager.getConnection(url);
+				Statement stmt = conn.createStatement();
+				ResultSet rs = stmt.executeQuery("select not_a_column from animal")) {
+			while (rs.next())
+				System.out.println(rs.getString(1));
+		} catch (SQLException e) {
+			System.out.println(e.getMessage());
+			System.out.println(e.getSQLState());
+			System.out.println(e.getErrorCode());
+		}
+	}
+}