工作中用到的状态模式

状态模式涉及到的类有：
1.上下文，拥有一个或多个状态类实例，对客户端暴露接口；
2.状态接口，封装具体状态类所对应的行为；
3.具体状态类，真正实现状态行为。

类图如下：

微信截图_20181121143455.png

代码示例：
先看一下之前同事写的代码：

@Override  
    public List getDrlOperationDTO(String typeId) {  
        List list = Operation.list;  
        List operationList = new ArrayList<>();  
          
        //字符串类型(等于,不等于,被包含于,不被包含于,不为空,为空,匹配,不匹配)  
        if (DataType.STR.getValue().toString().equals(typeId)) {  
            for (int i = 0; i < list.size(); i++) {  
                if (!list.get(i).getIndex().equals(Operation.GRE.getIndex())  
                        && !list.get(i).getIndex().equals(Operation.GREEQL.getIndex())   
                        && !list.get(i).getIndex().equals(Operation.LESS.getIndex())   
                        && !list.get(i).getIndex().equals(Operation.LESSEQL.getIndex())   
                        && !list.get(i).getIndex().equals(Operation.BET.getIndex())  
                        && !list.get(i).getIndex().equals(Operation.CONTAINS.getIndex())   
                        && !list.get(i).getIndex().equals(Operation.EXCLUDES.getIndex())) {  
                    operationList.add(list.get(i));  
                }  
            }  
              
        //数值类型(等于,大于,大于等于,小于,小于等于,不等于,被包含于,不被包含于,不为空,为空)  
        } else if (DataType.INT.getValue().toString().equals(typeId) || DataType.FLOAT.getValue().toString().equals(typeId)  
                || DataType.DOUBLE.getValue().toString().equals(typeId)) {  
            for (int i = 0; i < list.size(); i++) {  
                if (!list.get(i).getIndex().equals(Operation.MATCHES.getIndex())   
                        && !list.get(i).getIndex().equals(Operation.NMATCHES.getIndex())   
                        && !list.get(i).getIndex().equals(Operation.BET.getIndex())  
                        && !list.get(i).getIndex().equals(Operation.CONTAINS.getIndex())   
                        && !list.get(i).getIndex().equals(Operation.EXCLUDES.getIndex())){  
                    operationList.add(list.get(i));  
                }    
            }  
              
        //布尔类型(等于,不等于,不为空,为空)  
        } else if (DataType.BOOLEAN.getValue().toString().equals(typeId)) {  
            for (int i = 0; i < list.size(); i++) {  
                if (list.get(i).getIndex().equals(Operation.EQL.getIndex())  
                        || list.get(i).getIndex().equals(Operation.NEQL.getIndex())  
                        || list.get(i).getIndex().equals(Operation.NULL.getIndex())   
                        || list.get(i).getIndex().equals(Operation.NOTNULL.getIndex())){  
                    operationList.add(list.get(i));  
                }  
            }  
              
        //数组类型(包含,不包含,不为空,为空)  
        } else if (DataType.STRS.getValue().toString().equals(typeId) || DataType.DOUBLES.getValue().toString().equals(typeId)  
                || DataType.INTS.getValue().toString().equals(typeId)) {  
            for (int i = 0; i < list.size(); i++) {  
                if (list.get(i).getIndex().equals(Operation.CONTAINS.getIndex())  
                        || list.get(i).getIndex().equals(Operation.EXCLUDES.getIndex())  
                        || list.get(i).getIndex().equals(Operation.NULL.getIndex())   
                        || list.get(i).getIndex().equals(Operation.NOTNULL.getIndex())){  
                    operationList.add(list.get(i));  
                }  
            }  
              
        //其他类型为所有操作符  
        } else {  
            operationList = list;  
        }  
        return RuleAssembler.toDrlOperationDtos(operationList);  
    }  

一堆if else看着就头疼，那么改成状态模式怎么做呢？

代码如下：

1.Context类

public class DrlOperatorContext {  
  
    private DrlOperatorState state;  
  
    private List operationList = new ArrayList<>();  
  
    public List getOperationList(){  
        return operationList;  
    }  
  
    public List addOperateList(String typeId) {  
  
        List list = Operation.list;  
  
        //字符串类型(等于,不等于,被包含于,不被包含于,不为空,为空,匹配,不匹配)  
        if (DataType.STR.getValue().toString().equals(typeId)) {  
            state = new DrlStrOperator();  
  
            //数值类型(等于,大于,大于等于,小于,小于等于,不等于,被包含于,不被包含于,不为空,为空)  
        } else if (DataType.INT.getValue().toString().equals(typeId) || DataType.FLOAT.getValue().toString().equals(typeId)  
                || DataType.DOUBLE.getValue().toString().equals(typeId)) {  
            state = new DrlNumberOperator();  
  
            //布尔类型(等于,不等于,不为空,为空)  
        } else if (DataType.BOOLEAN.getValue().toString().equals(typeId)) {  
  
            state = new DrlBooleanOperator();  
  
            //数组类型(包含,不包含,不为空,为空)  
        } else if (DataType.STRS.getValue().toString().equals(typeId) || DataType.DOUBLES.getValue().toString().equals(typeId)  
                || DataType.INTS.getValue().toString().equals(typeId)) {  
            state = new DrlArrayOperator();  
            //其他类型为所有操作符  
        } else {  
  
            operationList = list;  
        }  
  
        if (state != null) {  
            operationList = state.addOperateList(list, this);  
        }  
        return operationList;  
    }  
}  

2.State接口

public interface DrlOperatorState {  
  
    List addOperateList(List list, DrlOperatorContext context);  
}  

3.具体状态

public class DrlArrayOperator implements DrlOperatorState {  
  
    @Override  
    public List addOperateList(List list, DrlOperatorContext context) {  
        List  operationList = context.getOperationList();  
        for (int i = 0; i < list.size(); i++) {  
            if (list.get(i).getIndex().equals(Operation.CONTAINS.getIndex())  
                    || list.get(i).getIndex().equals(Operation.EXCLUDES.getIndex())  
                    || list.get(i).getIndex().equals(Operation.NULL.getIndex())  
                    || list.get(i).getIndex().equals(Operation.NOTNULL.getIndex())){  
                operationList.add(list.get(i));  
            }  
        }  
        return operationList;  
    }  
}  
  
public class DrlBooleanOperator implements DrlOperatorState{  
  
    @Override  
    public List addOperateList(List list, DrlOperatorContext context) {  
  
        List operationList = context.getOperationList();  
        for (int i = 0; i < list.size(); i++) {  
            if (list.get(i).getIndex().equals(Operation.EQL.getIndex())  
                    || list.get(i).getIndex().equals(Operation.NEQL.getIndex())  
                    || list.get(i).getIndex().equals(Operation.NULL.getIndex())  
                    || list.get(i).getIndex().equals(Operation.NOTNULL.getIndex())){  
                operationList.add(list.get(i));  
            }  
        }  
        return operationList;  
    }  
}  
  
public class DrlNumberOperator implements DrlOperatorState {  
  
    @Override  
    public List addOperateList(List list, DrlOperatorContext context) {  
  
        List operationList = context.getOperationList();  
  
        for (int i = 0; i < list.size(); i++) {  
            if (!list.get(i).getIndex().equals(Operation.MATCHES.getIndex())  
                    && !list.get(i).getIndex().equals(Operation.NMATCHES.getIndex())  
                    && !list.get(i).getIndex().equals(Operation.BET.getIndex())  
                    && !list.get(i).getIndex().equals(Operation.CONTAINS.getIndex())  
                    && !list.get(i).getIndex().equals(Operation.EXCLUDES.getIndex())){  
                operationList.add(list.get(i));  
            }  
        }  
  
        return operationList;  
    }  
}  
  
  
public class DrlStrOperator implements DrlOperatorState {  
  
    @Override  
    public List addOperateList(List list, DrlOperatorContext context) {  
  
        List operationList = context.getOperationList();  
  
        for (int i = 0; i < list.size(); i++) {  
            if (!list.get(i).getIndex().equals(Operation.GRE.getIndex())  
                    && !list.get(i).getIndex().equals(Operation.GREEQL.getIndex())  
                    && !list.get(i).getIndex().equals(Operation.LESS.getIndex())  
                    && !list.get(i).getIndex().equals(Operation.LESSEQL.getIndex())  
                    && !list.get(i).getIndex().equals(Operation.BET.getIndex())  
                    && !list.get(i).getIndex().equals(Operation.CONTAINS.getIndex())  
                    && !list.get(i).getIndex().equals(Operation.EXCLUDES.getIndex())) {  
                operationList.add(list.get(i));  
            }  
        }  
        return operationList;  
    }  
}  

4.客户端调用

@Override  
    public List getDrlOperationDTO(String typeId) {  
        DrlOperatorContext context = new DrlOperatorContext();  
        List operationList = context.addOperateList(typeId);  
        return RuleAssembler.toDrlOperationDtos(operationList);  
    }  

这样大大简化了，客户端的调用方式，提高了代码的也读性，同时需要增加新的类型只需要实现State接口即可。