spring jdbcTemplate源码剖析

　　本文浅析 spring jdbcTemplate 源码，主要是学习其设计精髓。模板模式、巧妙的回调

一、jdbcTemplate 类结构

①、JdbcOperations : 接口定义了方法，如

<T> T execute(StatementCallback<T> action) throws DataAccessException;

void execute(String sql) throws DataAccessException;

<T> T query(String sql, ResultSetExtractor<T> rse) throws DataAccessException;

。。。

②、JdbcAccessor ：定义了数据源。

③、实现JdbcOperations接口定义的方法

二、jdbcTemplate 模板模式

1、我们看下execute(StatementCallback<T> action)实现（核心）

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); // 回调

            handleWarnings(stmt);

            return result;

        }

        catch (SQLException ex) {

            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());

        }

    }

2、再看下 execute(String sql) 源码

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 {

                stmt.execute(sql); // JAVA  jdbc

                return null;

            }

            @Override

            public String getSql() {

                return sql;

            }

        }

        execute(new ExecuteStatementCallback()); // 调用上述T execute(StatementCallback<T> action) 

    }

由此，可以知道，我们平时常用的execute(final String sql) 方法，底层帮我们做了很多事情，如创建默认的ExecuteStatementCallback，采用回调的方式，由模板去执行sql，关闭链接

3、T query(final String sql, final ResultSetExtractor<T> rse) 源码实现

@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());

    }

4、update(final String sql) 源码

@Override

    public int update(final String sql) throws DataAccessException {

        Assert.notNull(sql, "SQL must not be null");

        if (logger.isDebugEnabled()) {

            logger.debug("Executing SQL update [" + sql + "]");

        }

        class UpdateStatementCallback implements StatementCallback<Integer>, SqlProvider {

            @Override

            public Integer doInStatement(Statement stmt) throws SQLException {

                int rows = stmt.executeUpdate(sql);

                if (logger.isDebugEnabled()) {

                    logger.debug("SQL update affected " + rows + " rows");

                }

                return rows;

            }

            @Override

            public String getSql() {

                return sql;

            }

        }

        return execute(new UpdateStatementCallback());

    }

巴特西

spring jdbcTemplate源码剖析

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