设计模式学习之过滤器模式

什么是过滤器模式？

        这种模式允许开发人员使用不同的标准来过滤一组对象，通过逻辑运算以解耦的方式把它们连接起来。

过滤器模式的关键是什么？

        过滤器模式比较容易，通过过滤器实现过滤，关键就是我们的filter的逻辑，我们举一个简单的例子，如下图所示：

        我们的computer包括有cpu，memory、disk等，然后我们通过AMDCpuFilter过滤出所有使用AMD牌子CPU的computer。代码如下所示：

Computer类：

public class Computer {    private String cup;    private String disk;    private String memory;    public Computer(String cup, String disk, String memory) {        this.cup = cup;        this.disk = disk;        this.memory = memory;    }    public String getCup() {        return cup;    }    public void setCup(String cup) {        this.cup = cup;    }    public String getDisk() {        return disk;    }    public void setDisk(String disk) {        this.disk = disk;    }    public String getMemory() {        return memory;    }    public void setMemory(String memory) {        this.memory = memory;    }    public void show() {        System.out.println("computer cpu = " + cup + ", disk = " + disk + ", memory = " + memory);    }}

Filter类：

public interface Filter {    public List<Computer> execute(List<Computer> computerList);}

AMDCpuFilter

public class AMDCpuFilter implements Filter {    @Override    public List<Computer> execute(List<Computer> computerList) {        List<Computer> interList = Lists.newArrayList();        for (Computer computer:computerList) {            if ("AMD".equals(computer.getCup())) {                interList.add(computer);            }        }        return interList;    }}

InterCpuFilter类：

public class InterCpuFilter implements Filter {    @Override    public List<Computer> execute(List<Computer> computerList) {        List<Computer> interList = Lists.newArrayList();        for (Computer computer:computerList) {            if ("INTER".equals(computer.getCup())) {                interList.add(computer);            }        }        return interList;    }}

SeagateDiskFilter类：

public class SeagateDiskFilter implements Filter {    @Override    public List<Computer> execute(List<Computer> computerList) {        List<Computer> interList = Lists.newArrayList();        for (Computer computer:computerList) {            if ("SEAGATE".equals(computer.getDisk())) {                interList.add(computer);            }        }        return interList;    }}

client代码：

public class FilterDemo {    public static void main(String[] args) {        List<Computer> computerList = Lists.newArrayList();        computerList.add(new Computer("INTER", "WG", "GEIL"));        computerList.add(new Computer("INTER", "SEAGATE", "KINGSTON"));        computerList.add(new Computer("AMD", "SEAGATE", "KINGSTON"));        computerList.add(new Computer("AMD", "TOSHIBA", "HP"));        AMDCpuFilter amdFilter = new AMDCpuFilter();        InterCpuFilter interFilter = new InterCpuFilter();        SeagateDiskFilter seagateFilter = new SeagateDiskFilter();        List<Computer> amdList = amdFilter.execute(computerList);        List<Computer> interList = interFilter.execute(computerList);        List<Computer> seagateList = seagateFilter.execute(computerList);        System.out.println("AMD:");        print(amdList);        System.out.println("INTER");        print(interList);        System.out.println("SEAGATE:");        print(seagateList);    }    public static void print(List<Computer> computerList) {        for (Computer computer:computerList) {            computer.show();        }    }}

最终输出为：

AMD:computer cpu = AMD, disk = SEAGATE, memory = KINGSTONcomputer cpu = AMD, disk = TOSHIBA, memory = HPINTERcomputer cpu = INTER, disk = WG, memory = GEILcomputer cpu = INTER, disk = SEAGATE, memory = KINGSTONSEAGATE:computer cpu = INTER, disk = SEAGATE, memory = KINGSTONcomputer cpu = AMD, disk = SEAGATE, memory = KINGSTON

最终我们可以有一个过滤器聚合类进行多聚合器的管理，有FilterChain类：

public class FilterChain {    private List<Filter> filterList = Lists.newArrayList();    public void add(Filter filter) {        filterList.add(filter);    }    public List<Computer> execute(List<Computer> computerList) {        List<Computer> resultList = computerList;        for (Filter filter:filterList) {            resultList = filter.execute(resultList);        }        return resultList;    }}

client类中代码为：

        System.out.println("CHAIN:");        FilterChain chain = new FilterChain();        chain.add(new AMDCpuFilter());        chain.add(new SeagateDiskFilter());        List<Computer> chainList = chain.execute(computerList);        print(chainList);

最终结果为：

CHAIN:  computer cpu = AMD, disk = SEAGATE, memory = KINGSTON