设计模式之构建者模式(Builder):初步理解
构建者(Builder)设计模式(又叫生成器设计模式):
当一个类的内部数据过于复杂的时候(通常是负责持有数据的类,比如Config、VO、PO、Entity...),要创建的话可能就需要了解这个类的内部结构,还有这些东西是怎么组织装配等一大坨乱七八糟的东西,这个时候就会增加学习成本而且会很混乱,这个时候就想啊想一种什么法子来管理一下这个类中的数据呢,怎么在创建的时候让它按部就班的来,并且代码可读性很好别让我看花了眼啊,我要的东西也能都很好设置进来,这就是Builder模式的应用场景,Builder模式可以将一个类的构建和表示进行分离。
看一个例子:
public class Student { private int id;
private String name;
private String passwd;
private String sex;
private String address; // 构造器尽量缩小范围
private Student() {
} // 构造器尽量缩小范围
private Student(Student origin) {
// 拷贝一份
this.id = origin.id;
this.name = origin.name;
this.passwd = origin.passwd;
this.sex = origin.sex;
this.address = origin.address;
} public int getId() {
return id;
} public String getName() {
return name;
} public String getPasswd() {
return passwd;
} public String getSex() {
return sex;
} public String getAddress() {
return address;
} /**
* Student的创建完全依靠Student.Builder,使用一种方法链的方式来创建
*
*/
public static class Builder { private Student target; public Builder() {
target = new Student();
} public Builder address(int id) {
target.id = id;
return this;
} public Builder name(String name) {
target.name = name;
return this;
} public Builder password(String passwd) {
target.passwd = passwd;
return this;
} public Builder sex(String sex) {
target.sex = sex;
return this;
} public Builder address(String address) {
target.address = address;
return this;
} public Student build() {
return new Student(target);
} } }
Student并不是直接new出来的,对其构造器进行了处理使其可访问范围尽可能的小,只让它通过Student.Builder来构建自己,在Student.Builder中提供了一种类set的方法链的方式来设置值,然后在最后的build()方法的时候会返回一个Student对象,现在要创建一个Student对象,代码如下:
Student s=new Student.Builder().name("CC").password("qwerty").sex("男").address("银河系第二旋臂").build();
再对比一下如果不使用构造者模式(一般情况下的用法):
/**
* 学生实体
* @author CC11001100
*
*/
public class Student { private int id;
private String name;
private String passwd;
private String sex;
private String address; public Student() {
} public Student(String name, String passwd, String sex, String address) {
super();
this.name = name;
this.passwd = passwd;
this.sex = sex;
this.address = address;
} public int getId() {
return id;
} public void setId(int id) {
this.id = id;
} public String getName() {
return name;
} public void setName(String name) {
this.name = name;
} public String getPasswd() {
return passwd;
} public void setPasswd(String passwd) {
this.passwd = passwd;
} public String getSex() {
return sex;
} public void setSex(String sex) {
this.sex = sex;
} public String getAddress() {
return address;
} public void setAddress(String address) {
this.address = address;
} }
创建对象:
Student s=new Student("CC","qwerty","男","银河系第二旋臂");
对比一下进行一个优劣性分析:
一般的套路:优点是比较简单,开发效率高,缺点是如果参数真的很多的话鬼知道每个对应的是什么意思啊。
Builder模式:优点是可以将构造器的setter方法名取成类似注释的方式,这样我们可以很清晰的知道刚才究竟设置的什么值,可读性较高,缺点是比较冗长。
总结:初步的理解Builder模式解决了要设置的参数过多不好管理的问题(感觉每次构建不同对象是废话 - -)。
从Struts2框架中拿出来的两个Builder模式的例子(都是Config类):
ActionConfig :
public class ActionConfig extends Located implements Serializable { public static final String WILDCARD = "*"; protected List<InterceptorMapping> interceptors; // a list of interceptorMapping Objects eg. List<InterceptorMapping>
protected Map<String,String> params;
protected Map<String, ResultConfig> results;
protected List<ExceptionMappingConfig> exceptionMappings;
protected String className;
protected String methodName;
protected String packageName;
protected String name;
protected Set<String> allowedMethods; protected ActionConfig(String packageName, String name, String className) {
this.packageName = packageName;
this.name = name;
this.className = className;
params = new LinkedHashMap<String, String>();
results = new LinkedHashMap<String, ResultConfig>();
interceptors = new ArrayList<InterceptorMapping>();
exceptionMappings = new ArrayList<ExceptionMappingConfig>();
allowedMethods = new HashSet<String>();
allowedMethods.add(WILDCARD);
} /**
* Clones an ActionConfig, copying data into new maps and lists
* @param orig The ActionConfig to clone
* @Since 2.1
*/
protected ActionConfig(ActionConfig orig) {
this.name = orig.name;
this.className = orig.className;
this.methodName = orig.methodName;
this.packageName = orig.packageName;
this.params = new LinkedHashMap<String,String>(orig.params);
this.interceptors = new ArrayList<InterceptorMapping>(orig.interceptors);
this.results = new LinkedHashMap<String,ResultConfig>(orig.results);
this.exceptionMappings = new ArrayList<ExceptionMappingConfig>(orig.exceptionMappings);
this.allowedMethods = new HashSet<String>(orig.allowedMethods);
} public String getName() {
return name;
} public String getClassName() {
return className;
} public List<ExceptionMappingConfig> getExceptionMappings() {
return exceptionMappings;
} public List<InterceptorMapping> getInterceptors() {
return interceptors;
} public Set<String> getAllowedMethods() {
return allowedMethods;
} /**
* Returns name of the action method
*
* @return name of the method to execute
*/
public String getMethodName() {
return methodName;
} /**
* @return Returns the packageName.
*/
public String getPackageName() {
return packageName;
} public Map<String, String> getParams() {
return params;
} public Map<String, ResultConfig> getResults() {
return results;
} public boolean isAllowedMethod(String method) {
if (allowedMethods.size() == 1 && WILDCARD.equals(allowedMethods.iterator().next())) {
return true;
} else {
return allowedMethods.contains(method);
}
} @Override public boolean equals(Object o) {
if (this == o) {
return true;
} if (!(o instanceof ActionConfig)) {
return false;
} final ActionConfig actionConfig = (ActionConfig) o; if ((className != null) ? (!className.equals(actionConfig.className)) : (actionConfig.className != null)) {
return false;
} if ((name != null) ? (!name.equals(actionConfig.name)) : (actionConfig.name != null)) {
return false;
} if ((interceptors != null) ? (!interceptors.equals(actionConfig.interceptors)) : (actionConfig.interceptors != null))
{
return false;
} if ((methodName != null) ? (!methodName.equals(actionConfig.methodName)) : (actionConfig.methodName != null)) {
return false;
} if ((params != null) ? (!params.equals(actionConfig.params)) : (actionConfig.params != null)) {
return false;
} if ((results != null) ? (!results.equals(actionConfig.results)) : (actionConfig.results != null)) {
return false;
} if ((allowedMethods != null) ? (!allowedMethods.equals(actionConfig.allowedMethods)) : (actionConfig.allowedMethods != null)) {
return false;
} return true;
} @Override public int hashCode() {
int result;
result = (interceptors != null ? interceptors.hashCode() : 0);
result = 31 * result + (params != null ? params.hashCode() : 0);
result = 31 * result + (results != null ? results.hashCode() : 0);
result = 31 * result + (exceptionMappings != null ? exceptionMappings.hashCode() : 0);
result = 31 * result + (className != null ? className.hashCode() : 0);
result = 31 * result + (methodName != null ? methodName.hashCode() : 0);
result = 31 * result + (packageName != null ? packageName.hashCode() : 0);
result = 31 * result + (name != null ? name.hashCode() : 0);
result = 31 * result + (allowedMethods != null ? allowedMethods.hashCode() : 0);
return result;
} @Override public String toString() {
StringBuilder sb = new StringBuilder();
sb.append("{ActionConfig ");
sb.append(name).append(" (");
sb.append(className);
if (methodName != null) {
sb.append(".").append(methodName).append("()");
}
sb.append(")");
sb.append(" - ").append(location);
sb.append("}");
return sb.toString();
} /**
* The builder for this object. An instance of this object is the only way to construct a new instance. The
* purpose is to enforce the immutability of the object. The methods are structured in a way to support chaining.
* After setting any values you need, call the {@link #build()} method to create the object.
*/
public static class Builder implements InterceptorListHolder{ private ActionConfig target; public Builder(ActionConfig toClone) {
target = new ActionConfig(toClone);
} public Builder(String packageName, String name, String className) {
target = new ActionConfig(packageName, name, className);
} public Builder packageName(String name) {
target.packageName = name;
return this;
} public Builder name(String name) {
target.name = name;
return this;
} public Builder className(String name) {
target.className = name;
return this;
} public Builder defaultClassName(String name) {
if (StringUtils.isEmpty(target.className)) {
target.className = name;
}
return this;
} public Builder methodName(String method) {
target.methodName = method;
return this;
} public Builder addExceptionMapping(ExceptionMappingConfig exceptionMapping) {
target.exceptionMappings.add(exceptionMapping);
return this;
} public Builder addExceptionMappings(Collection<? extends ExceptionMappingConfig> mappings) {
target.exceptionMappings.addAll(mappings);
return this;
} public Builder exceptionMappings(Collection<? extends ExceptionMappingConfig> mappings) {
target.exceptionMappings.clear();
target.exceptionMappings.addAll(mappings);
return this;
} public Builder addInterceptor(InterceptorMapping interceptor) {
target.interceptors.add(interceptor);
return this;
} public Builder addInterceptors(List<InterceptorMapping> interceptors) {
target.interceptors.addAll(interceptors);
return this;
} public Builder interceptors(List<InterceptorMapping> interceptors) {
target.interceptors.clear();
target.interceptors.addAll(interceptors);
return this;
} public Builder addParam(String name, String value) {
target.params.put(name, value);
return this;
} public Builder addParams(Map<String,String> params) {
target.params.putAll(params);
return this;
} public Builder addResultConfig(ResultConfig resultConfig) {
target.results.put(resultConfig.getName(), resultConfig);
return this;
} public Builder addResultConfigs(Collection<ResultConfig> configs) {
for (ResultConfig rc : configs) {
target.results.put(rc.getName(), rc);
}
return this;
} public Builder addResultConfigs(Map<String,ResultConfig> configs) {
target.results.putAll(configs);
return this;
} public Builder addAllowedMethod(String methodName) {
target.allowedMethods.add(methodName);
return this;
} public Builder addAllowedMethod(Collection<String> methods) {
target.allowedMethods.addAll(methods);
return this;
} public Builder location(Location loc) {
target.location = loc;
return this;
} public ActionConfig build() {
target.params = Collections.unmodifiableMap(target.params);
target.results = Collections.unmodifiableMap(target.results);
target.interceptors = Collections.unmodifiableList(target.interceptors);
target.exceptionMappings = Collections.unmodifiableList(target.exceptionMappings);
target.allowedMethods = Collections.unmodifiableSet(target.allowedMethods);
ActionConfig result = target;
target = new ActionConfig(target);
return result;
}
}
}
ExceptionMappingConfig:
public class ExceptionMappingConfig extends Located implements Serializable { private String name;
private String exceptionClassName;
private String result;
private Map<String,String> params; protected ExceptionMappingConfig(String name, String exceptionClassName, String result) {
this.name = name;
this.exceptionClassName = exceptionClassName;
this.result = result;
this.params = new LinkedHashMap<String,String>();
} protected ExceptionMappingConfig(ExceptionMappingConfig target) {
this.name = target.name;
this.exceptionClassName = target.exceptionClassName;
this.result = target.result;
this.params = new LinkedHashMap<String,String>(target.params);
} public String getName() {
return name;
} public String getExceptionClassName() {
return exceptionClassName;
} public String getResult() {
return result;
} public Map<String,String> getParams() {
return params;
} @Override
public boolean equals(Object o) {
if (this == o) {
return true;
} if (!(o instanceof ExceptionMappingConfig)) {
return false;
} final ExceptionMappingConfig exceptionMappingConfig = (ExceptionMappingConfig) o; if ((name != null) ? (!name.equals(exceptionMappingConfig.name)) : (exceptionMappingConfig.name != null)) {
return false;
} if ((exceptionClassName != null) ? (!exceptionClassName.equals(exceptionMappingConfig.exceptionClassName)) : (exceptionMappingConfig.exceptionClassName != null))
{
return false;
} if ((result != null) ? (!result.equals(exceptionMappingConfig.result)) : (exceptionMappingConfig.result != null))
{
return false;
} if ((params != null) ? (!params.equals(exceptionMappingConfig.params)) : (exceptionMappingConfig.params != null))
{
return false;
} return true;
} @Override
public int hashCode() {
int hashCode;
hashCode = ((name != null) ? name.hashCode() : 0);
hashCode = (29 * hashCode) + ((exceptionClassName != null) ? exceptionClassName.hashCode() : 0);
hashCode = (29 * hashCode) + ((result != null) ? result.hashCode() : 0);
hashCode = (29 * hashCode) + ((params != null) ? params.hashCode() : 0); return hashCode;
} /**
* The builder for this object. An instance of this object is the only way to construct a new instance. The
* purpose is to enforce the immutability of the object. The methods are structured in a way to support chaining.
* After setting any values you need, call the {@link #build()} method to create the object.
*/
public static class Builder{ private ExceptionMappingConfig target; public Builder(ExceptionMappingConfig toClone) {
target = new ExceptionMappingConfig(toClone);
} public Builder(String name, String exceptionClassName, String result) {
target = new ExceptionMappingConfig(name, exceptionClassName, result);
} public Builder name(String name) {
target.name = name;
return this;
} public Builder exceptionClassName(String name) {
target.exceptionClassName = name;
return this;
} public Builder result(String result) {
target.result = result;
return this;
} public Builder addParam(String name, String value) {
target.params.put(name, value);
return this;
} public Builder addParams(Map<String,String> params) {
target.params.putAll(params);
return this;
} public Builder location(Location loc) {
target.location = loc;
return this;
} public ExceptionMappingConfig build() {
target.params = Collections.unmodifiableMap(target.params);
ExceptionMappingConfig result = target;
target = new ExceptionMappingConfig(target);
return result;
}
} }
参考资料:
设计模式之构建者模式(Builder):初步理解的更多相关文章
- 构建者模式Builder创建对象
构建者(Builder)设计模式(又叫生成器设计模式): 当一个类的内部数据过于复杂的时候(通常是负责持有数据的类,比如Config.VO.PO.Entity...),要创建的话可能就需要了解这个类的 ...
- 深入探索Java设计模式之构建器模式(五)
抽丝剥茧 细说架构那些事——[优锐课] 简单的程序不需要大量的设计过程,因为它们只关注有限的解决方案,仅使用几个类.大型程序专注于广泛的设计,该设计比好的设计范例的任何其他属性都更能利用可重用性.宏伟 ...
- 设计模式系列之建造者模式(Builder Pattern)——复杂对象的组装与创建
说明:设计模式系列文章是读刘伟所著<设计模式的艺术之道(软件开发人员内功修炼之道)>一书的阅读笔记.个人感觉这本书讲的不错,有兴趣推荐读一读.详细内容也可以看看此书作者的博客https:/ ...
- Net设计模式实例之建造者模式(Builder Pattern)
一.建造者模式简介(Brief Introduction) 建造者模式(Builder Pattern),将一个复杂对象的构建与它的表示分离,使的同样的构建过程可以创建不同的表示. 建造者模式的优点是 ...
- 【原】iOS设计模式之:建造者模式Builder Pattern,用于改进初始化参数
本文主要讨论一下iOS中的Builder Pattern.与网上很多版本不同,本文不去长篇大论地解释建造者模式的概念,那些东西太虚了.设计模式这种东西是为了解决实际问题的,不能为了设计模式而设计模式, ...
- iOS设计模式之:建造者模式Builder Pattern,用于改进初始化参数
转自:http://www.cnblogs.com/wengzilin/p/4365855.html 本文主要讨论一下iOS中的Builder Pattern.与网上很多版本不同,本文不去长篇大论地解 ...
- 构建者模式(Builder pattern)
构建者模式应用场景: 主要用来构建一些复杂对象,这里的复杂对象比如说:在建造大楼时,需要先打牢地基,搭建框架,然后自下向上地一层一层盖起来.通常,在建造这种复杂结构的物体时,很难一气呵成.我们需要首先 ...
- IOS设计模式浅析之建造者模式(Builder)
定义 "将一个复杂对象的构建与它的表现分离,使得同样的构建过程可以创建不同的表现". 最初的定义出现于<设计模式>(Addison-Wesley,1994). 看这个概 ...
- 设计模式 笔记 生成器(建造者)模式 Builder
//---------------------------15/04/08---------------------------- //builder 生成器(建造者)模式---对象创建型模式 /* ...
随机推荐
- Linux 动态监听进程shell
背景 前几天在研究线程的时候,看到一句话说java里的线程Thread.run都会在Linux中fork一个的轻量级进程,于是就想验证一下(笔者的机器是Linux的).当时用top命令的时候,进程总是 ...
- << CocoaPods安装和使用教程 >>github code4app以及cocoachina 苹果官方文档
developer.apple.com 英文搜索各个技术的官方介绍文档, 前提是英文过关 cocoachina ios最新新闻, 信息 code4app上有许多组件 http://www.code4a ...
- OpenCv椭圆皮肤模型
Mat input_image; Mat output_mask; Mat output_image; void main() { VideoCapture cam(); if (!cam.isOpe ...
- 2016年11月5日--marquee标签、插入百度地图
<marquee></marquee>可以实现多种滚动效果,无需js控制. 使用marquee标记不仅可以移动文字,也可以移动图片,表格等. 语法:<marquee> ...
- Python自动化之select、greenlet和gevent和事件驱动模型初探
进程.线程和协程的区别 进程拥有自己独立的堆和栈,既不共享堆,亦不共享栈,进程由操作系统调度. 线程拥有自己独立的栈和共享的堆,共享堆,不共享栈,线程亦由操作系统调度(标准线程是的). 协程和线程一样 ...
- [转]mysql分布式方案-分库拆表
来源:http://kissthink.com/archive/mysql-distributed-programs---and-warehouses-split-table.html 分库& ...
- Hifiman:一个国产音频厂商的忧伤[转]
一则苹果计划32亿美元收购音频设备厂商Beats的消息,让音频设备——这个极少被人们重视又时刻离不开的产品重新引发了关注. 国产数码品牌通常都被自然的贴上低端.低质的标签.然而难能可贵的是,国产音频设 ...
- phpcms访问顶级栏目,自动跳到第一个子栏目
在顶级栏目的category页放入如下代码: <?php if($child){ $child_arrary=explode(',',$arrchildid); $to_url=$CATEGOR ...
- nginx配置多域名映射方法(本地hosts)
本地测试网站的时候如果不想用localhost/xxxx的形式访问,可能就需要修改hosts文件来映射了,但是一个网站还好,假如有多个网站的话就不行了. 这时就需要配置多域名映射 比如hosts中配置 ...
- join
一句话 join(param) 是把 array 连城一个字符串,中间用 param隔开