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Composite

介绍

定义:将对象组合成树形结构来表示“整体/部分”的层次结构。组合能让客户以一致的方式处理个别对象及对象组合。GoF:Compose objects into tree structure to represent part-whole hierarchies. Composite lets client treat individual objects and compositions of object uniformly.
优点:清楚地定义分层次的复杂对象,表示对象的全部或者部分层次。

类图

  • Component:组件,包括叶节点和组合两种。
  • Leaf:叶节点。
  • Composite:组合,持有一群孩子,孩子可以是组合也可以是叶节点。

源码

MyBatis 源码,org.apache.ibatis.scripting.xmltags
public interface SqlNode {
boolean apply(DynamicContext context);
}
public class MixedSqlNode implements SqlNode {
private List<SqlNode> contents;
public MixedSqlNode(List<SqlNode> contents) {
this.contents = contents;
}
@Override
public boolean apply(DynamicContext context) {
for (SqlNode sqlNode : contents) {
sqlNode.apply(context);
}
return true;
}
}
public class WhereSqlNode extends TrimSqlNode {
private static List<String> prefixList = Arrays.asList("AND ","OR ","AND\n", "OR\n", "AND\r", "OR\r", "AND\t", "OR\t");
public WhereSqlNode(Configuration configuration, SqlNode contents) {
super(configuration, contents, "WHERE", prefixList, null, null);
}
}
  • SqlNode:对应 Component。
  • WhereSqlNode:对应 Leaf。
  • MixedSqlNode:对应 Composite。
Last modified 2yr ago