概述
本文将用用责任链模式实现一条指挥链路。首领发令给将军，将军传令给指挥官，指挥官再传令给士兵。首领、将军、指挥官、士兵形成一条指挥链路。
代码实现
首先我们定义Request和RequestType。
public class Request {
private final RequestType requestType;
private final String requestDescription;
private boolean handled;
public Request(final RequestType requestType, final String requestDescription) {
this.requestType = Objects.requireNonNull(requestType);
this.requestDescription = Objects.requireNonNull(requestDescription);
}
public String getRequestDescription() { return requestDescription; }
public RequestType getRequestType() { return requestType; }
public void markHandled() { this.handled = true; }
public boolean isHandled() { return this.handled; }
@Override
public String toString() { return getRequestDescription(); }
}
public enum RequestType {
DEFEND_CASTLE, TORTURE_PRISONER, COLLECT_TAX
}然后我们定义抽象类RequestHandler及其实现类OrcCommander，OrcOfficer和OrcSoldier代码是和OrcCommander及其类似的，不再赘述。OrcKing不仅掌握了将军、指挥官和士兵，还实现了命令的传递。
public abstract class RequestHandler {
private final RequestHandler next;
public RequestHandler(RequestHandler next) {
this.next = next;
}
public void handleRequest(Request req) {
if (next != null) {
next.handleRequest(req);
}
}
protected void printHandling(Request req) {
LOGGER.info("{} handling request \"{}\"", this, req);
}
@Override
public abstract String toString();
}
public class OrcCommander extends RequestHandler {
public OrcCommander(RequestHandler handler) {
super(handler);
}
@Override
public void handleRequest(Request req) {
if (req.getRequestType().equals(RequestType.DEFEND_CASTLE)) {
printHandling(req);
req.markHandled();
} else {
super.handleRequest(req);
}
}
@Override
public String toString() {
return "Orc commander";
}
}
public class OrcKing {
RequestHandler chain;
public OrcKing() {
buildChain();
}
private void buildChain() {
chain = new OrcCommander(new OrcOfficer(new OrcSoldier(null)));
}
public void makeRequest(Request req) {
chain.handleRequest(req);
}
}实际调用如下
var king = new OrcKing();
king.makeRequest(new Request(RequestType.DEFEND_CASTLE, "defend castle"));
king.makeRequest(new Request(RequestType.TORTURE_PRISONER, "torture prisoner"));
king.makeRequest(new Request(RequestType.COLLECT_TAX, "collect tax"));控制台输出如下，这样就实现了一条完整的指挥链路。
Orc commander handling request "defend castle"
Orc officer handling request "torture prisoner"
Orc soldier handling request "collect tax"
使用场景
- 不局限于一个对象能够处理请求。
- 无需指定具体的请求对象。
- 处理请求的对象能够灵活切换。