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《Spring技术内幕》笔记-第五章 数据库操作组件的实现

时间：2021-07-01 10:21:17 帮助过：3人阅读

  • public void execute(final String sql) throws DataAccessException {
  • if (logger.isDebugEnabled()) {
  • logger.debug("Executing SQL statement [" + sql + "]");
  • }
  • class ExecuteStatementCallback implements StatementCallback<Object>, SqlProvider {
  • @Override
  • public Object doInStatement(Statement stmt) throws SQLException {//重写
  • stmt.execute(sql);
  • return null;
  • }
  • @Override
  • public String getSql() {
  • return sql;
  • }
  • }
  • execute(new ExecuteStatementCallback());
  • }
    1. @Override
    2. 	public <T> T execute(StatementCallback<T> action) throws DataAccessException {
    3. 		Assert.notNull(action, "Callback object must not be null");
    5. 		Connection con = DataSourceUtils.getConnection(getDataSource());//获取COnnection
    6. 		Statement stmt = null;
    7. 		try {
    8. 			Connection conToUse = con;
    9. 			if (this.nativeJdbcExtractor != null &&
    10. 					this.nativeJdbcExtractor.isNativeConnectionNecessaryForNativeStatements()) {
    11. 				conToUse = this.nativeJdbcExtractor.getNativeConnection(con);
    12. 			}
    13. 			stmt = conToUse.createStatement();//Statement
    14. 			applyStatementSettings(stmt);
    15. 			Statement stmtToUse = stmt;
    16. 			if (this.nativeJdbcExtractor != null) {
    17. 				stmtToUse = this.nativeJdbcExtractor.getNativeStatement(stmt);
    18. 			}
    19. 			T result = action.doInStatement(stmtToUse);//调用传入接口的子类的实现
    20. 			handleWarnings(stmt);
    21. 			return result;
    22. 		}
    23. 		catch (SQLException ex) {
    24. 			// Release Connection early, to avoid potential connection pool deadlock
    25. 			// in the case when the exception translator hasn‘t been initialized yet.
    26. 			JdbcUtils.closeStatement(stmt);
    27. 			stmt = null;
    28. 			DataSourceUtils.releaseConnection(con, getDataSource());
    29. 			con = null;
    30. 			throw getExceptionTranslator().translate("StatementCallback", getSql(action), ex);
    31. 		}
    32. 		finally {
    33. 			JdbcUtils.closeStatement(stmt);
    34. 			DataSourceUtils.releaseConnection(con, getDataSource());
    35. 		}
    36. 	}

    4，JdbcTemplate的query方法

    1. @Override
    2. 	public <T> T query(final String sql, final ResultSetExtractor<T> rse) throws DataAccessException {
    3. 		Assert.notNull(sql, "SQL must not be null");
    4. 		Assert.notNull(rse, "ResultSetExtractor must not be null");
    5. 		if (logger.isDebugEnabled()) {
    6. 			logger.debug("Executing SQL query [" + sql + "]");
    7. 		}
    8. 		class QueryStatementCallback implements StatementCallback<T>, SqlProvider {
    9. 			@Override
    10. 			public T doInStatement(Statement stmt) throws SQLException {//内部类重写此方法
    11. 				ResultSet rs = null;
    12. 				try {
    13. 					rs = stmt.executeQuery(sql);
    14. 					ResultSet rsToUse = rs;
    15. 					if (nativeJdbcExtractor != null) {
    16. 						rsToUse = nativeJdbcExtractor.getNativeResultSet(rs);
    17. 					}
    18. 					return rse.extractData(rsToUse);
    19. 				}
    20. 				finally {
    21. 					JdbcUtils.closeResultSet(rs);
    22. 				}
    23. 			}
    24. 			@Override
    25. 			public String getSql() {
    26. 				return sql;
    27. 			}
    28. 		}
    29. 		return execute(new QueryStatementCallback());
    30. 	}

    我们查看在execute方法中的，发现最终调用的是doInStatement，该方法均在内部类中重写。

    5，使用Connection。

        ?Spring通过DataSourceUtils对Connection进行管理。在数据库应用中，数据库的Connection的使用往往和事务处理相关。


    1. public static Connection getConnection(DataSource dataSource) throws CannotGetJdbcConnectionException {
    2. 		try {
    3. 			return doGetConnection(dataSource);
    4. 		}
    5. 		catch (SQLException ex) {
    6. 			throw new CannotGetJdbcConnectionException("Could not get JDBC Connection", ex);
    7. 		}
    8. 	}

    1. public static Connection doGetConnection(DataSource dataSource) throws SQLException {
    2. 		Assert

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