java使用策略模式代替if/else

平時在開發中避免不了使用大量的if else語句,但過多層的if else對於性能有很大的開銷,相似以下代碼java

public class MainStart {

    public static void main(String[] args) {
        String msgid = "MS066";
        if(message.equals("MS066")){
            System.out.println("MS066");
        }else if (message.equals("MS034")){
            System.out.println("MS034");
        }else if (message.equals("MS064")){
            System.out.println("MS064");
        }else{
            System.out.println("no msgid!");
        }
    }
}

上邊代碼只是示例,實際狀況可能不止4層算法

策略模式是一種解耦的方法,它對算法進行封裝,使得算法的調用和算法自己分離。使用策略模式客戶端代碼不須要調整,算法之間能夠互相替換,由於不一樣的算法實現的是同一個接口。將上面的代碼優化後變爲:sql

public class MainStart {

    public static void main(String[] args) {
     OrderDictController controller=new OrderDictController(); String msgid
= "MS066"; MsgInterface msgInterface=MsgContext.getInstance(msgId);
     msgInterface.manage(msg,controller);
} }

實現策略模式須要如下幾個步驟:dom

1.定義接口ide

import java.sql.SQLException;

import org.dom4j.DocumentException;

import com.huc.controller.OrderDictController;

public interface MsgInterface {
    public void manage(String msg, OrderDictController controller) throws DocumentException, SQLException;
}

2.實現接口,重寫處理邏輯性能

package com.huc.msg.imp;

import java.sql.SQLException;

import org.dom4j.DocumentException;

import com.huc.controller.OrderDictController;
import com.huc.msg.MsgInterface;

public class MS003 implements MsgInterface{
    @Override
    public void manage(String msg, OrderDictController controller) throws DocumentException, SQLException {
        controller.manageMs003(msg);
    }
}
package com.huc.msg.imp;

import java.sql.SQLException;

import org.dom4j.DocumentException;

import com.huc.controller.OrderDictController;
import com.huc.msg.MsgInterface;

public class MS028 implements MsgInterface{
    @Override
    public void manage(String msg, OrderDictController controller) throws DocumentException, SQLException {
        controller.manageMs028(msg);
    }
}

寫兩個做爲例子,可根據狀況自行擴展實現類優化

3.定義策略上下文,根據msgid獲取對象實例this

package com.huc.msg;

import java.util.Map;

public class MsgContext {
    public static MsgInterface getInstance(String msgId){
        MsgInterface inter=null;
        Map<String, String> allClazz = MsgEnum.getAllClazz();
        String clazz = allClazz.get(msgId);
        if (msgId!=null&&msgId.trim().length()>0) {
            try {
                try {
                    inter = (MsgInterface) Class.forName(clazz).newInstance();//調用無參構造器建立實例
                } catch (InstantiationException e) {
                    e.printStackTrace();
                } catch (IllegalAccessException e) {
                    e.printStackTrace();
                }
            } catch (ClassNotFoundException e) {
                e.printStackTrace();
            }
        }
        return inter;
    }
}

在這一步驟中,咱們須要一種方式能夠根據msgid來反射獲取對象的實例,這裏使用枚舉來維護兩者的對應關係。spa

package com.huc.msg;

import java.util.HashMap;
import java.util.Map;

public enum MsgEnum {

    MS066("MS066", "com.huc.msg.imp.MS066"),
    MS034("MS034", "com.huc.msg.imp.MS034"),
    MS064("MS064", "com.huc.msg.imp.MS064"),
    MS028("MS028", "com.huc.msg.imp.MS028"),
    MS003("MS003", "com.huc.msg.imp.MS003"),
    MS062("MS062", "com.huc.msg.imp.MS062"),
    MS154("MS154", "com.huc.msg.imp.MS154"),
    MS153("MS153", "com.huc.msg.imp.MS153"),
    MS033("MS033", "com.huc.msg.imp.MS033");
    private String msgid;
    private String clazz;

    public static Map<String, String> getAllClazz() {
        Map<String, String> map = new HashMap<String, String>();
        for (MsgEnum msgEnum : MsgEnum.values()) {
            map.put(msgEnum.getMsgid(), msgEnum.getClazz());
        }
        return map;
    }


    MsgEnum(String msgid, String clazz) {
        this.msgid = msgid;
        this.clazz = clazz;
    }


    public String getMsgid() {
        return msgid;
    }


    public void setMsgid(String msgid) {
        this.msgid = msgid;
    }


    public String getClazz() {
        return clazz;
    }

    public void setClazz(String clazz) {
        this.clazz = clazz;
    }

}

在上面的代碼中,getAllClazz()方法用於獲取全部message和對應處理類的映射關係。至此策略模式優化就已經完成了,運行MainStart能夠看到運行結果。code

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