spring-jdbc

1.先复习下jdbc

2.spring-jdbc

<beans xmlns="http://www.springframework.org/schema/beans" 
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
        xsi:schemaLocation="http://www.springframework.org/schema/beans 
                            http://www.springframework.org/schema/beans/spring-beans-4.0.xsd">

　　　　<!--定义数据源，这里定义spring-jdbc的DriverManagerDataSource-->

　    <bean id="springDSN" class="org.springframework.jdbc.datasource.DriverManagerDataSource">

        　<property name="url" value="jdbc:mysql://...."/>

        <property name="username" value="..."></property>
        <property name="password" value="..."></property>
    </bean>
    <!--操作JDBC的类-->
    <bean id="jdbcTemplate" class="org.springframework.jdbc.core.JdbcTemplate">
        <property name="dataSource" ref="springDSN"/>
    </bean>
    
    <bean id="testDao" class="TestDao">
       <property name="jdbcTem" ref="jdbcTemplate"/>
    </bean>
</beans>

public class TestDao {
    
    private JdbcTemplate jdbcT;
    
    public void setJdbcTem(JdbcTemplate jdbc){
        this.jdbcT = jdbc;
    }
    
    public void selectName() {
        String sql = "select * from table where id = 19";
        List list = jdbcT.queryForList(sql);
        System.out.println(list.get(0));
    }
}

跟踪org.springframework.jdbc.core.JdbcTemplate

    @Override
    public List<Map<String, Object>> queryForList(String sql) throws DataAccessException {
        return query(sql, getColumnMapRowMapper());
    }    
    @Override
    public <T> List<T> query(String sql, RowMapper<T> rowMapper) throws DataAccessException {
        return query(sql, new RowMapperResultSetExtractor<T>(rowMapper));
    }
    @Override
    public <T> T query(final String sql, final ResultSetExtractor<T> rse) throws DataAccessException {
        Assert.notNull(sql, "SQL must not be null");
        Assert.notNull(rse, "ResultSetExtractor must not be null");
        if (logger.isDebugEnabled()) {
            logger.debug("Executing SQL query [" + sql + "]");
        }
        class QueryStatementCallback implements StatementCallback<T>, SqlProvider {
            @Override
            public T doInStatement(Statement stmt) throws SQLException {
                ResultSet rs = null;
                try {
                    rs = stmt.executeQuery(sql);
                    ResultSet rsToUse = rs;
                    if (nativeJdbcExtractor != null) {
                        rsToUse = nativeJdbcExtractor.getNativeResultSet(rs);
                    }
                    return rse.extractData(rsToUse);
                }
                finally {
                    JdbcUtils.closeResultSet(rs);
                }
            }
            @Override
            public String getSql() {
                return sql;
            }
        }
        return execute(new QueryStatementCallback());
    }

    @Override
    public <T> T execute(StatementCallback<T> action) throws DataAccessException {
        Assert.notNull(action, "Callback object must not be null");

        Connection con = DataSourceUtils.getConnection(getDataSource());
        Statement stmt = null;
        try {
            Connection conToUse = con;
            if (this.nativeJdbcExtractor != null &&
                    this.nativeJdbcExtractor.isNativeConnectionNecessaryForNativeStatements()) {
                conToUse = this.nativeJdbcExtractor.getNativeConnection(con);
            }
            stmt = conToUse.createStatement();
            applyStatementSettings(stmt);
            Statement stmtToUse = stmt;
            if (this.nativeJdbcExtractor != null) {
                stmtToUse = this.nativeJdbcExtractor.getNativeStatement(stmt);
            }
            T result = action.doInStatement(stmtToUse);
            handleWarnings(stmt);
            return result;
        }
        catch (SQLException ex) {
            // Release Connection early, to avoid potential connection pool deadlock
            // in the case when the exception translator hasn't been initialized yet.
            JdbcUtils.closeStatement(stmt);
            stmt = null;
            DataSourceUtils.releaseConnection(con, getDataSource());
            con = null;
            throw getExceptionTranslator().translate("StatementCallback", getSql(action), ex);
        }
        finally {
            JdbcUtils.closeStatement(stmt);
            DataSourceUtils.releaseConnection(con, getDataSource());
        }
    }

 

跟踪代码，先看看DriverManagerDataSource获取链接，用的是DriverManager.getConnection

    /**
     * Getting a Connection using the nasty static from DriverManager is extracted
     * into a protected method to allow for easy unit testing.
     * @see java.sql.DriverManager#getConnection(String, java.util.Properties)
     */
    protected Connection getConnectionFromDriverManager(String url, Properties props) throws SQLException {
        return DriverManager.getConnection(url, props);
    }

再看看它处理resultSet

public class RowMapperResultSetExtractor<T> implements ResultSetExtractor<List<T>> {
    @Override
    public List<T> extractData(ResultSet rs) throws SQLException {
        List<T> results = (this.rowsExpected > 0 ? new ArrayList<T>(this.rowsExpected) : new ArrayList<T>());
        int rowNum = 0;
        while (rs.next()) {
            results.add(this.rowMapper.mapRow(rs, rowNum++));
        }
        return results;
    }
}

public class ColumnMapRowMapper implements RowMapper<Map<String, Object>> {

    @Override
    public Map<String, Object> mapRow(ResultSet rs, int rowNum) throws SQLException {
        ResultSetMetaData rsmd = rs.getMetaData();
        int columnCount = rsmd.getColumnCount();
        Map<String, Object> mapOfColValues = createColumnMap(columnCount);
        for (int i = 1; i <= columnCount; i++) {
            String key = getColumnKey(JdbcUtils.lookupColumnName(rsmd, i));
            Object obj = getColumnValue(rs, i);
            mapOfColValues.put(key, obj);
        }
        return mapOfColValues;
    }
}