`jdbc`包

背景知识

• 模版模式
• 易用性

讲解

模版模式

某些类通用的一些处理方法一致，但是处理对象可能存在不同，此时可以使用模版方法，抽取父类编写通用处理方法，子类只需实现获取对象的方法即可。

public class SQL extends AbstractSQL<SQL> {

    @Override
    public SQL getSelf() {
        return this;
    }

}
public abstract class AbstractSQL<T> {

    private static final String AND = ") \nAND (";
    private static final String OR = ") \nOR (";

    private final SQLStatement sql = new SQLStatement();

    public abstract T getSelf();

    public T UPDATE(String table) {
        sql().statementType = SQLStatement.StatementType.UPDATE;
        sql().tables.add(table);
        return getSelf();
    }

    public T SET(String sets) {
        sql().sets.add(sets);
        return getSelf();
    }
		......
}

以上代码可知：

1. 若用户需要自定SQL 如  ExplainSQL，从而进行性能调优，此时只需要继承 AbstractSQL即可，而无需编写原方法。

易用性

为了用户使用方便和构建 SQL的直观性，AbstractSQL命名采用了全大写的模式，以此让用户更加易用。

SqlRunner类

    public int insert(String sql, Object... args) throws SQLException {
        PreparedStatement ps;
        if (useGeneratedKeySupport) {
            ps = connection.prepareStatement(sql, Statement.RETURN_GENERATED_KEYS);
        } else {
            ps = connection.prepareStatement(sql);
        }

        try {
            setParameters(ps, args);
            ps.executeUpdate();
            if (useGeneratedKeySupport) {
                List<Map<String, Object>> keys = getResults(ps.getGeneratedKeys());
                if (keys.size() == 1) {
                    Map<String, Object> key = keys.get(0);
                    Iterator<Object> i = key.values().iterator();
                    if (i.hasNext()) {
                        Object genkey = i.next();
                        if (genkey != null) {
                            try {
                                return Integer.parseInt(genkey.toString());
                            } catch (NumberFormatException e) {
                                //ignore, no numeric key support
                            }
                        }
                    }
                }
            }
            return NO_GENERATED_KEY;
        } finally {
            try {
                ps.close();
            } catch (SQLException e) {
                //ignore
            }
        }
    }

    public int update(String sql, Object... args) throws SQLException {
        PreparedStatement ps = connection.prepareStatement(sql);
        try {
            setParameters(ps, args);
            return ps.executeUpdate();
        } finally {
            try {
                ps.close();
            } catch (SQLException e) {
                //ignore
            }
        }
    }

此类在Mybatis中没有任何的使用，此类应该只是为了提供给用户，让用户可以自定义执行相关 SQL，分析其方法本质为原始JDBC相关操作流程。

ScriptRunner类

   private void executeFullScript(Reader reader) {
        StringBuilder script = new StringBuilder();
        try {
            BufferedReader lineReader = new BufferedReader(reader);
            String line;
            while ((line = lineReader.readLine()) != null) {
                script.append(line);
                script.append(LINE_SEPARATOR);
            }
            String command = script.toString();
            println(command);
            executeStatement(command);
            commitConnection();
        } catch (Exception e) {
            String message = "Error executing: " + script + ".  Cause: " + e;
            printlnError(message);
            throw new RuntimeSqlException(message, e);
        }
    }

    private void executeLineByLine(Reader reader) {
        StringBuilder command = new StringBuilder();
        try {
            BufferedReader lineReader = new BufferedReader(reader);
            String line;
            while ((line = lineReader.readLine()) != null) {
                handleLine(command, line);
            }
            commitConnection();
            checkForMissingLineTerminator(command);
        } catch (Exception e) {
            String message = "Error executing: " + command + ".  Cause: " + e;
            printlnError(message);
            throw new RuntimeSqlException(message, e);
        }
    }
    private void handleLine(StringBuilder command, String line) throws SQLException {
        String trimmedLine = line.trim();
        if (lineIsComment(trimmedLine)) {
            Matcher matcher = DELIMITER_PATTERN.matcher(trimmedLine);
            if (matcher.find()) {
                delimiter = matcher.group(5);
            }
            println(trimmedLine);
        } else if (commandReadyToExecute(trimmedLine)) {
            command.append(line.substring(0, line.lastIndexOf(delimiter)));
            command.append(LINE_SEPARATOR);
            println(command);
            executeStatement(command.toString());
            command.setLength(0);
        } else if (trimmedLine.length() > 0) {
            command.append(line);
            command.append(LINE_SEPARATOR);
        }
    }

此类的核心方法如上，可看出其本质和SqlRunner类一致。