Builder模式功能是组装复杂的实例，重点关注过程，一共存在3个角色：Bulider（建造者）、 ConcreteBuilder（具体建造者）、 Dirctor（监工）
使用Builder模式编写文档，定义Builder的子类:
- TextBuilder: 使用纯文本编写文档
- HTMLBuilder: 使用HTML编写文档
UML
示例代码
Builder
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| public abstract class Builder {
protected abstract void makeTitle(String title);
protected abstract void makeString(String str);
protected abstract void close();
}
|
TextBuilder
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| public class TextBuilder extends Builder{
private StringBuffer buffer = new StringBuffer();
@Override
protected void makeTitle(String title) {
buffer.append("==============================\n");
buffer.append("『" + title + "』\n");
buffer.append("\n");
}
@Override
protected void makeString(String str) {
buffer.append('■' + str + "\n");
buffer.append("\n");
}
@Override
protected void close() {
buffer.append("==============================\n");
}
public String getResult() {
return buffer.toString();
}
}
|
HTMLBuilder
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| public class HTMLBuilder extends Builder {
private String filename;
private PrintWriter writer;
@Override
protected void makeTitle(String title) {
filename = title + ".html";
try {
writer = new PrintWriter(new FileWriter(filename));
} catch (IOException e) {
e.printStackTrace();
}
writer.println("<html><head><title>" + title + "</title></head><body>");
writer.println("<h1>" + title + "</h1>");
}
@Override
protected void makeString(String str) {
writer.println("<p>" + str + "</p>");
}
@Override
protected void close() {
writer.println("</body></html>");
writer.close();
}
public String getResult() {
return filename;
}
}
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Director
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| public class Director {
private Builder builder;
public Director(Builder builder) {
this.builder = builder;
}
public void construct() {
builder.makeTitle("Greeting");
builder.makeString("从早上到下午");
builder.close();
}
}
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Main
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| public class Main {
public static void main(String[] args) {
TextBuilder textBuilder = new TextBuilder();
Director director = new Director(textBuilder);
director.construct();
System.out.println(textBuilder.getResult());
HTMLBuilder htmlBuilder = new HTMLBuilder();
director = new Director(htmlBuilder);
director.construct();
System.out.println(htmlBuilder.getResult());
}
}
|
Builder需要有相同的生产过程，且有部件需要生产，而工厂模式一般没有，更侧重生产结果。
抽象工厂通过不同的构建过程生成不同的对象，而Builder模式通过相同的构建过程生成不同的对象。
builder 也是一个高层建筑，但是他和Abstract Factory侧重点不同，Abstract Factory侧重于创建东西的结果，而builder侧重的是创建东西的过程。当你需要做一系列有序的工作来完成创建一个对象时 builder就派上用场啦