开源组件：（3）dbutils

DbUtils类的主要作用是：关闭资源、加载驱动。

QueryRunner类，位于org.apache.commons.dbutils包下，全名org.apache.commons.dbutils.QueryRunner

QueryRunner类是组件的核心工具类：定义了所有的与数据库操作的方法(查询、更新)

对于QueryRunner类的描述是Executes SQL queries with pluggable strategies for handling ResultSets. This class is thread safe.

下面的话，要多读几遍：

【Executes SQL queries】 with 【pluggable strategies】 for 【handling ResultSets】.

QueryRunner类提供了默认的构造函数：public QueryRunner() ，在进行update、query等方式法需要传入Connection对象

QueryRunner类还提供了另外一个构造函数，接受DataSource类型的对象：public QueryRunner(DataSource ds) 

对这个构造函数的描述是：Constructor for QueryRunner that takes a DataSource to use. Methods that do not take a Connection parameter will retrieve connections from this DataSource.使用不带Connnection参数的方法时，将从DataSource中获取Connection对象。

提供的update方法（带有Connection）

（1）public int update(Connection conn, String sql)

//描述：Execute an SQL INSERT, UPDATE, or DELETE query without replacement parameters.

（2）public int update(Connection conn, String sql, Object param) 

//描述：Execute an SQL INSERT, UPDATE, or DELETE query with a single replacement parameter.

（3）public int update(Connection conn, String sql, Object... params)

//描述：Execute an SQL INSERT, UPDATE, or DELETE query.

提供的update方法（不带有Connection）

（1）public int update(String sql)

//描述：Executes the given INSERT, UPDATE, or DELETE SQL statement without any replacement parameters. The Connection is retrieved from the DataSource set in the constructor. This Connection must be in auto-commit mode or the update will not be saved.

（2）public int update(String sql, Object param)

//描述：Executes the given INSERT, UPDATE, or DELETE SQL statement with a single replacement parameter. The Connection is retrieved from the DataSource set in the constructor. This Connection must be in auto-commit mode or the update will not be saved.

（3）public int update(String sql, Object... params)

//描述：Executes the given INSERT, UPDATE, or DELETE SQL statement. The Connection is retrieved from the DataSource set in the constructor. This Connection must be in auto-commit mode or the update will not be saved.

提供的query方法（带Connection对象）

（1）public <T> T query(Connection conn, String sql, ResultSetHandler<T> rsh)

//描述：Execute an SQL SELECT query without any replacement parameters. The caller is responsible for closing the connection.

（2）public <T> T query(Connection conn, String sql, ResultSetHandler<T> rsh, Object... params) 

//描述：Execute an SQL SELECT query with replacement parameters. The caller is responsible for closing the connection.

提供的query方法（不带有Connection）

（1）public <T> T query(String sql, ResultSetHandler<T> rsh)

//描述：Executes the given SELECT SQL without any replacement parameters. The Connection is retrieved from the DataSource set in the constructor.

（2）public <T> T query(String sql, ResultSetHandler<T> rsh, Object... params)

//描述：Executes the given SELECT SQL query and returns a result object. The Connection is retrieved from the DataSource set in the constructor.

update部分的源码

所有public修饰的update方法都会调用丰面这个方法。注意第二个参数boolean closeConn

private int update(Connection conn, boolean closeConn, String sql, Object... params)

   
    public int update(Connection conn, String sql) throws SQLException {
        return this.update(conn, false, sql, (Object[]) null);
    }

    
    public int update(Connection conn, String sql, Object param) throws SQLException {
        return this.update(conn, false, sql, new Object[]{param});
    }

    
    public int update(Connection conn, String sql, Object... params) throws SQLException {
        return update(conn, false, sql, params);
    }

    
    public int update(String sql) throws SQLException {
        Connection conn = this.prepareConnection();

        return this.update(conn, true, sql, (Object[]) null);
    }

    
    public int update(String sql, Object param) throws SQLException {
        Connection conn = this.prepareConnection();

        return this.update(conn, true, sql, new Object[]{param});
    }

    
    public int update(String sql, Object... params) throws SQLException {
        Connection conn = this.prepareConnection();

        return this.update(conn, true, sql, params);
    }

    
    private int update(Connection conn, boolean closeConn, String sql, Object... params) throws SQLException {
        if (conn == null) {
            throw new SQLException("Null connection");
        }

        if (sql == null) {
            if (closeConn) {
                close(conn);
            }
            throw new SQLException("Null SQL statement");
        }

        PreparedStatement stmt = null;
        int rows = 0;

        try {
            stmt = this.prepareStatement(conn, sql);
            this.fillStatement(stmt, params);
            rows = stmt.executeUpdate();

        } catch (SQLException e) {
            this.rethrow(e, sql, params);

        } finally {
            close(stmt);
            if (closeConn) {
                close(conn);
            }
        }

        return rows;
    }

query部分的源码

所有的public修饰的query方法都会调用下面的方法。注意第二个参数boolean closeConn

private <T> T query(Connection conn, boolean closeConn, String sql, ResultSetHandler<T> rsh, Object... params)

    
    public <T> T query(Connection conn, String sql, ResultSetHandler<T> rsh, Object... params) throws SQLException {
        return this.<T>query(conn, false, sql, rsh, params);
    }

    
    public <T> T query(Connection conn, String sql, ResultSetHandler<T> rsh) throws SQLException {
        return this.<T>query(conn, false, sql, rsh, (Object[]) null);
    }

    
    public <T> T query(String sql, ResultSetHandler<T> rsh, Object... params) throws SQLException {
        Connection conn = this.prepareConnection();

        return this.<T>query(conn, true, sql, rsh, params);
    }

    
    public <T> T query(String sql, ResultSetHandler<T> rsh) throws SQLException {
        Connection conn = this.prepareConnection();

        return this.<T>query(conn, true, sql, rsh, (Object[]) null);
    }

    
    private <T> T query(Connection conn, boolean closeConn, String sql, ResultSetHandler<T> rsh, Object... params)
            throws SQLException {
        if (conn == null) {
            throw new SQLException("Null connection");
        }

        if (sql == null) {
            if (closeConn) {
                close(conn);
            }
            throw new SQLException("Null SQL statement");
        }

        if (rsh == null) {
            if (closeConn) {
                close(conn);
            }
            throw new SQLException("Null ResultSetHandler");
        }

        PreparedStatement stmt = null;
        ResultSet rs = null;
        T result = null;

        try {
            stmt = this.prepareStatement(conn, sql);
            this.fillStatement(stmt, params);
            rs = this.wrap(stmt.executeQuery());
            result = rsh.handle(rs);

        } catch (SQLException e) {
            this.rethrow(e, sql, params);

        } finally {
            try {
                close(rs);
            } finally {
                close(stmt);
                if (closeConn) {
                    close(conn);
                }
            }
        }

        return result;
    }