第二十六章 Main组件
在每个系统里，都至少有一个这样的组件，创建，协调和监督其他组件，我称这种组件为Main组件。
终极细节
Main组件是最终细节，即最低层级的策略。这是系统的初始入口点。除了操作系统，什么都不依赖于它。它的任务是创建所有的工厂，策略和其他全局设施，然后把控制权交给系统的高层抽象部分。
在这个Main组件中，依赖关系应该由依赖注入框架注入。一旦它们被注入到Main中，Main就会正常地分配这些依赖关系，而不使用框架。
把Main当作所有脏组件中最脏的。1
考虑一下最新版本的寻找Wumpus中的以下主要组件。注意它是如何加载所有我们不希望代码的主体知道的字符串的。
public class Main implements HtwMessageReceiver {
private static HuntTheWumpus game;
private static int hitPoints = 10;
private static final List<String> caverns = new ArrayList<>();
private static final String[] environments = new String[]{
"bright",
"humid",
"dry",
"creepy",
"ugly",
"foggy",
"hot",
"cold",
"drafty",
"dreadful"
};
private static final String[] shapes = new String[] {
"round",
"square",
"oval",
"irregular",
"long",
"craggy",
"rough",
"tall",
"narrow"
};
private static final String[] cavernTypes = new String[] {
"cavern",
"room",
"chamber",
"catacomb",
"crevasse",
"cell",
"tunnel",
"passageway",
"hall",
"expanse"
};
private static final String[] adornments = new String[] {
"smelling of sulfur",
"with engravings on the walls",
"with a bumpy floor",
"",
"littered with garbage",
"spattered with guano",
"with piles of Wumpus droppings",
"with bones scattered around",
"with a corpse on the floor",
"that seems to vibrate",
"that feels stuffy",
"that fills you with dread"
};
现在这里有个main函数。注意它是如何使用HtwFactory创建游戏的。它以类名htw.game.HuntTheWumpusFade传递，因为这个类比Main更脏。这可以防止该类中的更改导致Main重新编译/重新部署。
public static void main(String[] args) throws IOException {
game = HtwFactory.makeGame("htw.game.HuntTheWumpusFacade",
new Main());
createMap();
BufferedReader br =
new BufferedReader(new InputStreamReader(System.in));
game.makeRestCommand().execute();
while (true) {
System.out.println(game.getPlayerCavern());
System.out.println("Health: " + hitPoints + " arrows: " +
game.getQuiver());
HuntTheWumpus.Command c = game.makeRestCommand();
System.out.println(">");
String command = br.readLine();
if (command.equalsIgnoreCase("e"))
c = game.makeMoveCommand(EAST);
else if (command.equalsIgnoreCase("w"))
c = game.makeMoveCommand(WEST);
else if (command.equalsIgnoreCase("n"))
c = game.makeMoveCommand(NORTH);
else if (command.equalsIgnoreCase("s"))
c = game.makeMoveCommand(SOUTH);
else if (command.equalsIgnoreCase("r"))
c = game.makeRestCommand();
else if (command.equalsIgnoreCase("sw"))
c = game.makeShootCommand(WEST);
else if (command.equalsIgnoreCase("se"))
c = game.makeShootCommand(EAST);
else if (command.equalsIgnoreCase("sn"))
c = game.makeShootCommand(NORTH);
else if (command.equalsIgnoreCase("ss"))
c = game.makeShootCommand(SOUTH);
else if (command.equalsIgnoreCase("q"))
return;
c.execute();
}
}
注意main函数创建了输入流，包含了游戏的主循环，解析简单的输入指令，但随后移交给其他更高层的组件处理。
最后，注意main创建的map。
private static void createMap() {
int nCaverns = (int) (Math.random() * 30.0 + 10.0);
while (nCaverns-- > 0)
caverns.add(makeName());
for (String cavern : caverns) {
maybeConnectCavern(cavern, NORTH);
maybeConnectCavern(cavern, SOUTH);
maybeConnectCavern(cavern, EAST);
maybeConnectCavern(cavern, WEST);
}
String playerCavern = anyCavern();
game.setPlayerCavern(playerCavern);
game.setWumpusCavern(anyOther(playerCavern));
game.addBatCavern(anyOther(playerCavern));
game.addBatCavern(anyOther(playerCavern));
game.addBatCavern(anyOther(playerCavern));
game.addPitCavern(anyOther(playerCavern));
game.addPitCavern(anyOther(playerCavern));
game.addPitCavern(anyOther(playerCavern));
game.setQuiver(5);
}
// much code removed…
}
重点在于，Main是干净架构最外层的脏的低层级模块。它将所有内容加载到高级系统中，然后手动控制它。
小结
将Main看作是应用程序的插件——一个插件，它设置初始条件和配置，收集所有外部资源，然后将其控制交到应用程序的高层级策略。由于它是一个插件，所以可能有许多Main组件，每个应用程序的配置都有一个。
例如，你可以建一个开发的Main插件，另一个用于测试，另一个用于生产。你也可以为每个部署到的国家/地区，每个管辖区域或每个客户分配一个Main插件。
当你将Main作为插件组件考虑时，支撑架构边界，配置问题变得更容易解决。
1. Think of Main as the dirtiest of all the dirty components. ↩