策略模式

/**
* Created by yaokj on 15-12-7.
*/
public interface Log {
public String log(String msg) throws Exception;
}

/**
* Created by yaokj on 15-12-7.
*/
public class DbLog implements Log {
@Override
public String log(String msg) throws Exception {
//制造异常，虽然无聊，但是只是为了测试
if(msg.length() > 5){
throw new Exception("信息长度过长。");
}
System.out.println("记录到数据库里的信息是："+msg);
return msg;
}
}

/**
* Created by yaokj on 15-12-7.
*/
public class FileLog implements Log {
@Override
public String log(String msg) {
System.out.println("记录到文件里的信息为："+msg);
return msg;
}
}

/**
* Created by yaokj on 15-12-7.
*/
public class StrategyContext {

public void log(String msg) throws Exception{
Log log = new DbLog();
try{
log.log(msg);
}catch (Exception e){
log = new FileLog();
log.log(msg);
}
}
}

/**
* Created by yaokj on 15-12-7.
*/
public class Client {
public static void main(String[] args) throws Exception {
StrategyContext context = new StrategyContext();
context.log("yaokj");
context.log("用户名为：yaokj");
}
}