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。

状态模式允许一个对象在其内部状态改变的时候改变其行为。

类图如下

 

代码示例：

先看一下之前同事写的代码：

@Override
	public List<DrlTypeDTO> getDrlOperationDTO(String typeId) {
		List<Operation> list = Operation.list;
		List<Operation> 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<Operation> operationList = new ArrayList<>();

    public List<Operation> getOperationList(){
        return operationList;
    }

    public List<Operation> addOperateList(String typeId) {

        List<Operation> 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<Operation> addOperateList(List<Operation> list, DrlOperatorContext context);
}

 3.具体状态

public class DrlArrayOperator implements DrlOperatorState {

    @Override
    public List<Operation> addOperateList(List<Operation> list, DrlOperatorContext context) {
        List<Operation>  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<Operation> addOperateList(List<Operation> list, DrlOperatorContext context) {

        List<Operation> 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<Operation> addOperateList(List<Operation> list, DrlOperatorContext context) {

        List<Operation> 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<Operation> addOperateList(List<Operation> list, DrlOperatorContext context) {

        List<Operation> 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<DrlTypeDTO> getDrlOperationDTO(String typeId) {
        DrlOperatorContext context = new DrlOperatorContext();
        List<Operation> 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。