design pattern reloaded

最新推荐文章于 2025-08-22 11:10:38 发布

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最新推荐文章于 2025-08-22 11:10:38 发布

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CC 4.0 BY-SA版权

文章标签：数据库

原文链接：http://www.cnblogs.com/grep/archive/2012/07/15/2592335.html

本文详细解析了Singleton模式的实现方式，并介绍了如何通过依赖注入来解决数据库调用的mock问题。此外，还讨论了如何使用接口和配置控制来改进代码的可维护性和可测试性。同时，文章涉及了Visitor模式的应用，展示了如何通过递归遍历文档结构并进行美化打印。本文旨在提供关于设计模式、依赖管理以及文档处理的最佳实践。

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Singleton

public final class Singleton{
private static Singleton INSTANCE = new Singleton();
private Singleton(){}
public static Singleton instance(){
return INSTANCE;
}
public Object read(){
//nasty database call
}
}

test :(

public class TestVictim{
public void testSomething(){
//holy crap, how do I mock the database call in Singleton?
}
}

interface to rescue

public interface Singleton{
Object read();
}

public class SingletonImpl implements Singleton{
public Object read(){
//...
}
}

//dependency injection, you are my hero.
public class Victim{
public final Singleton singleton;
public Victim(Singleton singleton){
this.singleton = singleton;
}
public void doSomething(){
Object foo = singleton.read();
}
}

learned:

interface and dependency injection

control by configuration

Visitor

public static boolean traverse_tree(BundleIContentTraverserVisitor visitor, IDocFrameworkSimpleNode n) {
        if (n == null)
            return false;
        if (!visitor.visitStart(n)) {
            return false;
        }
        for (IDocFrameworkSimpleNode sn: n.getSubnodes()) {
            traverse_tree(visitor, sn); 
        }
        if (!visitor.visitEnd(n)) {
            return false;
        }
        return true;
    }



    public void prettyPrint(final StringWriter sw) {
        traverse(new BundleIContentTraverserVisitor() {
            int m_indentation_level = 0;
            private void printIndent() {
                if (m_indentation_level <= 0)
                    return;
                for (int i=0; i < m_indentation_level; i++) {
                    sw.write("    ");            
                }
            }
            public boolean visitEnd(IDocFrameworkSimpleNode n) {
                m_indentation_level--;
                if (!(n instanceof TextNode)) {
                    printIndent();
                    sw.write("</"+n.getName()+">\n");
                }
                return true;
            }

            public boolean visitStart(IDocFrameworkSimpleNode n) {
                printIndent();
                m_indentation_level++;
                if (n instanceof TextNode) {
                    sw.write(n.getText());
                    sw.write("\n");
                }
                else {
                    sw.write("<"+n.getName());            
                    for (Map.Entry<String,String> me: n.getAttributes().entrySet()) {
                        sw.write(" "+me.getKey()+"=\""+me.getValue()+"\"");
                    }
                    sw.write(">\n");
                }
                return true;
            }
        });
    }