有没有更好的方法来写这个？检查场景

所以我有这个代码检查4个参数（作者，标题，关键字和主题）为我正在进行的项目做一些动态sql查询生成，我只是想知道是否有人知道更好的方法写出来。我感觉这是一种非常低效的方式，但这样做很晚，而且我很累。请让我知道，如果你知道有更好的方法来做到这一点，那么这里只是一堆if/else case检查语句。有没有更好的方法来写这个？检查场景

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 
         } 
        } 
       }

来源

2012-03-17 noname

您可以查询+ = variableName;在if语句中，你可以使用三元运算符：例如： - query + =（conjunct [0] == 0？“AND”：“OR”）; query + = titleQ; – 2012-03-17 07:34:33

我知道一个非常棒的方式，'但它晚了，我很累';） – DaveFar 2012-03-17 11:44:57

此外，很多代码是“死”，即无法访问，只需将其放入最新版本的eclipse中，并启用所有警告。。 – Adam 2012-03-17 11:53:00

怎么样更加结构化和可扩展的方法，请参见下面的例子。顺便说一句，您不应该真正将用户输入直接放入SQL查询中 - 而是使用准备好的语句来设法防止注入攻击。

// 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);

来源

2012-03-17 11:50:46 Adam

哇，好多了。我绝对不应该在午夜过后写代码。同样，对于sql注入项目，我们不需要担心这个类，因此直接用户输入。感谢或你的帮助，你摇滚！ – noname 2012-03-18 00:43:17

a = _author ? authorQ : 1; 
t = _title ? titleQ : 1; 
k = _keyword ? keywordQ : 1; 
s = _subject ? subjectQ : 1; 

c1 = conjunct[0] ? " OR " : " AND "; 
c2 = conjunct[1] ? " OR " : " AND "; 
c3 = conjunct[2] ? " OR " : " AND "; 

query += a + c1 + t + c2 + k + c3 + s;

来源

2012-03-17 08:10:28

因此，对于_author == null和conunction [0]！= 0查询变为... 1或....那个sql查询计算的是什么？ – DaveFar 2012-03-17 11:43:34

有没有更好的方法来写这个？检查场景

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