Java鏈接數據庫 #05# SQL與代碼分離

索引

• 讀取html中的SQL語句
• 缺陷總結

在Java鏈接數據庫 #04#裏大概是這樣放sql語句的：

package org.sample.shop.db.queryrunner;

import org.sample.shop.db.queryrunner.statementfactory.StatementFactory;

// TODO sql一長可讀性變得很是很是差
public interface Statements {

    String ITEM_SAVE_ITEM = "INSERT INTO item(user_id, name, price, status, quantity) VALUES (?, ?, ?, ?, ?)";
    String ITEM_REMOVE_BY_ID = "DELETE FROM item WHERE id=?";
    String ITEM_UPDATE_BY_ID = "UPDATE item SET name=?, price=?, status=?, quantity=? WHERE id=?";
    String ITEM_GET_BY_ID = "SELECT id, user_id AS userId, name, price, status, quantity FROM item WHERE id=?";
    // order
    String ORDER_GET_BY_UID = "SELECT id, user_id AS userId, total FROM simple_order WHERE user_id=?";
    String ORDER_SAVE_ORDER = "INSERT INTO simple_order(user_id, total) VALUES(?, ?)";
    String ORDER_SAVE_ORDER_DETAIL = "INSERT INTO order_detail(order_id, item_id, user_id, quantity, price, status) VALUES(?, ?, ?, ?, ?, ?)";
    // order detail
    String ORDER_DETAIL_GET_BY_ORDER_ID = "SELECT id, order_id AS orderId, item_id AS itemId, user_id AS userId, quantity, price, status FROM order_detail WHERE order_id=?";
}

在簡單的程序裏這樣寫仍是挺方便的，然而單條sql語句一旦變長可讀性就會變得很是很是差。改起來也至關不方便。

我首先想到的解決辦法是：像mybatis同樣把sql放到單獨一個XML文件裏。因而，我簡單寫了個草稿程序添加DOM4J依賴開始嘗試。結果當我把sql字符串放到xml標籤裏卻被提示格式不對，解析起來也報錯。。。。。。

而後仔細看看，mybatis能正常解析xml依靠的是這個↓

我只是想把sql單獨放到文件裏，而且我但願：

• 方便閱讀和修改sql語句
• 方便Java解析文件並讀取sql語句

爲了節約學習成本，我腦洞一開。。。。就投機取巧地用html + jsoup作這件事了。

讀取html中的SQL語句

sql.html：

<sql id="ITEM_LIST_BY_UID_AND_STATUS">
    SELECT *
    FROM (
    SELECT rownum AS r, id, user_id AS userId, name, price, status, quantity
    FROM item
    WHERE user_id=? AND status=?
    )temp
    WHERE r >= ? AND r < ?
</sql>
<sql id="ITEM_SAVE_ITEM">
    INSERT INTO item(user_id, name, price, status, quantity)
    VALUES (?, ?, ?, ?, ?)
</sql>
<sql id="ITEM_REMOVE_BY_ID">
    DELETE FROM item
    WHERE id=?
</sql>
<sql id="ITEM_UPDATE_BY_ID">
    UPDATE item
    SET name=?, price=?, status=?, quantity=?
    WHERE id=?
</sql>
<sql id="ITEM_GET_BY_ID">
    SELECT id, user_id AS userId, name, price, status, quantity
    FROM item
    WHERE id=?
</sql>

/

StatementFactory.java：

package org.sample.shop.db.queryrunner.statementfactory;

import org.jsoup.Jsoup;
import org.jsoup.nodes.Document;
import org.jsoup.nodes.Element;

import java.io.File;
import java.io.IOException;

public class StatementFactory {
    private static final String PATHNAME = StatementFactory.class.getResource("/sql.html").getPath();
    private static final String CHAR_SET = "UTF-8";

    private static Document doc;

    static {
        File input = new File(PATHNAME);
        try {
            doc = Jsoup.parse(input, CHAR_SET, "");
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public static String getStatement(String statementId) {
        Element sql = doc.select(statementId).first();
        return sql.text();
    }
}

/

Statements.java（原來的Sql.java）：

package org.sample.shop.db.queryrunner;

import org.sample.shop.db.queryrunner.statementfactory.StatementFactory;

public interface Statements {
    // item
    String ITEM_LIST_BY_UID_AND_STATUS = StatementFactory.getStatement("#ITEM_LIST_BY_UID_AND_STATUS");
    String ITEM_SAVE_ITEM = StatementFactory.getStatement("#ITEM_SAVE_ITEM");
    String ITEM_REMOVE_BY_ID = StatementFactory.getStatement("#ITEM_REMOVE_BY_ID");
    String ITEM_UPDATE_BY_ID = StatementFactory.getStatement("#ITEM_UPDATE_BY_ID");
    String ITEM_GET_BY_ID = StatementFactory.getStatement("#ITEM_GET_BY_ID");;
}

PS. interface中常量和類中靜態域性質是同樣的！！

缺陷總結

這樣作雖然解決了一些問題，可是改進空間仍是至關大的。。。

例如說實際寫的時候須要來回在4個文件跳轉：

以及Statements.java和StatementFactory.java職能實際上是重合的。。只是暫時沒去把它們寫到一塊兒。

就。。有時間再搞吧。。。。。。。。。。。。。。。。