設計模式-建造者(Builder)
阿新 • • 發佈:2018-01-19
sequence intern value 技術分享 模式 mar pen ear nds 2018-1-18 by Atlas
- 應用場景
需要采取循序漸進組合復雜對象時。
- UML
用過elasticsearch java api的小夥伴,自然了解BoolQueryBuilder及其內部doXContext處理的對象都是Builder模式,這裏BoolQuerySearchBuilder是我給其上根據業務需要又做的一層封裝,也是Builder模式,形式上看就是Builder模式嵌套Builder模式。
- 標準示例
public class BoolQuerySearchBuilder extends AbstractSearchBuilder { private final BoolQueryBuilder boolQueryBuilder = new BoolQueryBuilder(); public BoolQuerySearchBuilder mustQueryBuilders(List<QueryBuilder> mustQueryBuilders){ // 所有分句都必須匹配,類比 SQL 的 AND if(mustQueryBuilders != null){ for(QueryBuilder queryBuilderTmp : mustQueryBuilders){ boolQueryBuilder.must(queryBuilderTmp); } } return this; } public BoolQuerySearchBuilder mustNotQueryBuilders(List<QueryBuilder> mustNotQueryBuilders){ // 所有分句都必須不匹配,類比 SQL 的 NOT if(mustNotQueryBuilders != null){ for(QueryBuilder queryBuilder : mustNotQueryBuilders){ boolQueryBuilder.mustNot(queryBuilder); } } return this; } public BoolQuerySearchBuilder shouldQueryBuilders(List<QueryBuilder> shouldQueryBuilders){ // 至少有一個分句匹配,類比 SQL 的 OR if(shouldQueryBuilders != null){ for(QueryBuilder queryBuilder : shouldQueryBuilders){ boolQueryBuilder.should(queryBuilder); } } return this; } @Override protected final QueryBuilder queryBuilder() { return boolQueryBuilder; } }
- boolQueryBuilder是復雜的對象。
- mustQueryBuilders、mustNotQueryBuilder、shouldQueryBuilders分別通過調用boolQueryBuilder的must、mustNot、should循環漸進的組合boolQueryBuilder對象。
- 循環漸進組合對象過程中返回外層建造者,直到建造者完成對象組合,返回建造的對象。
public class BoolQueryBuilder extends QueryBuilder implements BoostableQueryBuilder<BoolQueryBuilder> { private final List<QueryBuilder> mustClauses = new ArrayList<>(); private final List<QueryBuilder> mustNotClauses = new ArrayList<>(); private final List<QueryBuilder> shouldClauses = new ArrayList<>(); public BoolQueryBuilder must(QueryBuilder queryBuilder) { mustClauses.add(queryBuilder); return this; } public BoolQueryBuilder mustNot(QueryBuilder queryBuilder) { mustNotClauses.add(queryBuilder); return this; } public BoolQueryBuilder should(QueryBuilder queryBuilder) { shouldClauses.add(queryBuilder); return this; } protected void doXContent(XContentBuilder builder, Params params) throws IOException { builder.startObject("bool"); doXArrayContent("must", mustClauses, builder, params); doXArrayContent("filter", filterClauses, builder, params); doXArrayContent("must_not", mustNotClauses, builder, params); doXArrayContent("should", shouldClauses, builder, params); if (boost != -1) { builder.field("boost", boost); } if (disableCoord != null) { builder.field("disable_coord", disableCoord); } if (minimumShouldMatch != null) { builder.field("minimum_should_match", minimumShouldMatch); } if (adjustPureNegative != null) { builder.field("adjust_pure_negative", adjustPureNegative); } if (queryName != null) { builder.field("_name", queryName); } builder.endObject(); } // ... }
BoolQueryBuilder對象本身也是Builder模式,循序漸進的組合追加的must、mustNot、should然後最終生成包含邏輯格式的文本Content,整個過程就是elasticsearch根據查詢條件動態生成查詢命令文本的過程。
- 調用方具體執行對象建造如下:
public JSONObject search(JSONObject jsonObject) throws Exception { logger.info("elasticsearch request json data : [{}]", jsonObject.toString()); // ... // 通過建造者生成查詢命令,循序漸進組合對象不僅代碼整潔而且過程靈活多變 SearchBuilder searchBuilder = new BoolQuerySearchBuilder() .shouldQueryBuilders(shouldQueryBuilders(jsonObject)) .mustQueryBuilders(mustQueryBuilders(jsonObject)) .mustNotQueryBuilders(mustNotQueryBuilders(jsonObject)); // 根據查詢命令執行elasticsearch搜索並響應搜索結果 Map<String, Object> map = searchBuilder.mutiSearch(indexName, indexType, currentPage, pageSize); // ... logger.info("elasticsearch response json data : [{}]", data.toJSONString()); return data; }
- 案例鑒賞
public final class StringBuilder
extends AbstractStringBuilder
implements java.io.Serializable, CharSequence{
// ...
@Override
public StringBuilder append(Object obj) {
return append(String.valueOf(obj));
}
@Override
public StringBuilder append(String str) {
super.append(str);
return this;
}
@Override
public StringBuilder append(CharSequence s, int start, int end) {
super.append(s, start, end);
return this;
}
@Override
public StringBuilder append(char[] str) {
super.append(str);
return this;
}
// ...
@Override
public String toString() {
// 通過循序漸進組合追加的字符數組,創建String對象
return new String(value, 0, count);
}
}
abstract class AbstractStringBuilder implements Appendable, CharSequence {
/**
* 字符數組.
*/
char[] value;
// ...
public AbstractStringBuilder append(Object obj) {
return append(String.valueOf(obj));
}
public AbstractStringBuilder append(String str) {
if (str == null)
return appendNull();
int len = str.length();
ensureCapacityInternal(count + len);
str.getChars(0, len, value, count);
count += len;
return this;
}
public AbstractStringBuilder append(StringBuffer sb) {
if (sb == null)
return appendNull();
int len = sb.length();
ensureCapacityInternal(count + len);
sb.getChars(0, len, value, count);
count += len;
return this;
}
@Override
public AbstractStringBuilder append(CharSequence s, int start, int end) {
if (s == null)
s = "null";
if ((start < 0) || (start > end) || (end > s.length()))
throw new IndexOutOfBoundsException(
"start " + start + ", end " + end + ", s.length() "
+ s.length());
int len = end - start;
ensureCapacityInternal(count + len);
for (int i = start, j = count; i < end; i++, j++)
value[j] = s.charAt(i);
count += len;
return this;
}
public AbstractStringBuilder append(char[] str) {
int len = str.length;
ensureCapacityInternal(count + len);
System.arraycopy(str, 0, value, count, len);
count += len;
return this;
}
public AbstractStringBuilder append(char c) {
ensureCapacityInternal(count + 1);
value[count++] = c;
return this;
}
// ...
}
StringBuilder的append方法調用基類AbstractStringBuilder的append方法向value字符數組追加字符,最終通過value字符數組完成String對象的創建。
設計模式-建造者(Builder)