java - 有没有更好的方法来写这个？检查场景

Question

所以我有这段代码检查 4 个参数(作者、标题、关键字和主题)来为我正在处理的项目生成一些动态 sql 查询，我只是想知道是否有人知道更好的方法来写出来。我觉得这是一种非常低效的方法，但为时已晚，我累了。如果您知道任何更好的方法来做到这一点，请告诉我，此时它只是一堆 if/else 案例检查语句。

谢谢!




if(_author!=null)
 {
 query += authorQ;
 if(_title != null)
 {
 if(conjunct[0] == 0)
 {
 query += " AND ";
 query += titleQ;
 }
 else
 {
 query += " OR ";
 query += titleQ;
 }
 if(_keyword != null)
 {
 if(conjunct[1] == 0)
 {
 query += " AND ";
 query += keywordQ;
 }
 else
 {
 query += " OR ";
 query += keywordQ;
 }
 if(_subject != null)
 {
 if(conjunct[2] == 0)
 {
 query += " AND ";
 query += subjectQ;
 }
 else
 {
 query += " OR ";
 query += subjectQ;
 }
 } 
 }
 else
 {
 if(_subject != null)
 {
 if(conjunct[2] == 0)
 {
 query += " AND ";
 query += subjectQ;
 }
 else
 {
 query += " OR ";
 query += subjectQ;
 }
 } 
 }
 }//title = null
 else
 {
 if(_keyword != null)
 {
 if(conjunct[1] == 0)
 {
 query += " AND ";
 query += keywordQ;
 }
 else
 {
 query += " OR ";
 query += keywordQ;
 }
 if(_subject != null)
 {
 if(conjunct[2] == 0)
 {
 query += " AND ";
 query += subjectQ;
 }
 else
 {
 query += " OR ";
 query += subjectQ;
 }
 } 
 }
 else //keyword null
 {
 if(_subject != null)
 {
 if(conjunct[2] == 0)
 {
 query += " AND ";
 query += subjectQ;
 }
 else
 {
 query += " OR ";
 query += subjectQ;
 }
 }
 //if subject's null at this point we don't care
 }
 }
 }
 else //author null
 {
 if(_title != null)
 {
 if(conjunct[0] == 0)
 {
 query += " AND ";
 query += titleQ;
 }
 else
 {
 query += " OR ";
 query += titleQ;
 }
 if(_keyword != null)
 {
 if(conjunct[1] == 0)
 {
 query += " AND ";
 query += keywordQ;
 }
 else
 {
 query += " OR ";
 query += keywordQ;
 }
 if(_subject != null)
 {
 if(conjunct[2] == 0)
 {
 query += " AND ";
 query += subjectQ;
 }
 else
 {
 query += " OR ";
 query += subjectQ;
 }
 } 
 }
 else
 {
 if(_subject != null)
 {
 if(conjunct[2] == 0)
 {
 query += " AND ";
 query += subjectQ;
 }
 else
 {
 query += " OR ";
 query += subjectQ;
 }
 } 
 }
 }//title = null
 else
 {
 if(_keyword != null)
 {
 if(conjunct[1] == 0)
 {
 query += " AND ";
 query += keywordQ;
 }
 else
 {
 query += " OR ";
 query += keywordQ;
 }
 if(_subject != null)
 {
 if(conjunct[2] == 0)
 {
 query += " AND ";
 query += subjectQ;
 }
 else
 {
 query += " OR ";
 query += subjectQ;
 }
 } 
 }
 else //keyword null
 {
 if(_subject != null)
 {
 if(conjunct[2] == 0)
 {
 query += " AND ";
 query += subjectQ;
 }
 else
 {
 query += " OR ";
 query += subjectQ;
 }
 }
 //if subject's null at this point we don't care
 }
 }
 }

Answer 1

更结构化和可扩展的方法怎么样，请参见下面的示例。顺便说一句，您不应该真正将用户输入直接放入 SQL 查询中 - 使用准备好的语句来尝试防范注入(inject)攻击。

// test values
String _author = "authorfoo";
String _title = "titlebar";
String _keyword = null;
String _subject = "subjectfoo";
String authorQ = "author=" + _author;
String subjectQ = "subject=" + _subject;
String titleQ = "title="+ _title;
String keywordQ = "keyword=" + _keyword;
int conjunct[] = new int[]{ 0, 1, 1, 0};

// query building code
String []inputs = {_author, _title, _keyword, _subject};
String []queries = {authorQ, titleQ, keywordQ, subjectQ};
StringBuilder builder = new StringBuilder();
for (int i = 0 ; i < inputs.length; i++) {
    if (inputs[i] != null) {
        if (builder.length() > 0) { // don't start query with connective
            if (conjunct[i] == 0) {
                builder.append(" AND ");
            } else {
                builder.append(" OR ");
            }
        }
        builder.append(queries[i]);
    }
}
String query = builder.toString();
System.out.println(query);