目錄
- 1. 解題思路
- 2. 具體解析實(shí)現(xiàn)
- 3. 單元測試
用例：有一段sql語句，我們需要從中截取出所有字段部分，以便進(jìn)行后續(xù)的類型推斷或者別名字段抽取定義，請(qǐng)給出此解析方法。
想來很簡單吧，因?yàn)?sql 中的字段列表，使用方式有限，比如 a as b, a, a b...
1. 解題思路
如果不想做復(fù)雜處理，最容易想到的，就是直接用某個(gè)特征做分割即可。比如，先截取出 字段列表部分，然后再用逗號(hào)',' 分割，就可以得到一個(gè)個(gè)的字段了。然后再要細(xì)分，其實(shí)只需要用 as 進(jìn)行分割就可以了。
看起來好像可行，但是存在許多漏洞，首先，這里面有太多的假設(shè)：各種截取部分要求必須符合要求，必須沒有多余的逗號(hào)，必須要有as 等等。這明顯不符合要求了。
其二，我們可以換一種轉(zhuǎn)換方式。比如先截取到field部分，然后先以 as 分割，再以逗號(hào)分割，然后取最后一個(gè)詞作為field。
看起來好像更差了，截取到哪里已經(jīng)完全不知道了。即原文已經(jīng)被破壞殆盡，而且同樣要求要有 as 轉(zhuǎn)換標(biāo)簽，而且對(duì)于函數(shù)覬覦有 as 的場景，就完全錯(cuò)誤了。
其三，最好還是自行一個(gè)個(gè)單詞地解析，field 字段無外乎幾種情況，1. 普通字段如 select a; 2. 帶as的普通字段如 select a as b; 3. 帶函數(shù)的字段如 select coalesce(a, b); 4. 帶函數(shù)且?guī)s的字段如 select coalesce(a, b) ab; 5. 函數(shù)內(nèi)帶as的字段如 select cast(a as string) b; ... 我們只需依次枚舉對(duì)應(yīng)的情況，就可以將字段解析出來了。
看起來是個(gè)不錯(cuò)的想法。但是具體實(shí)現(xiàn)如何？
2. 具體解析實(shí)現(xiàn)
主要分兩個(gè)部分，1. 需要定義一個(gè)解析后的結(jié)果數(shù)據(jù)結(jié)構(gòu)，以便清晰描述字段信息； 2. 分詞解析sql并以結(jié)構(gòu)體返回；
我們先來看看整個(gè)算法核心：
/**
* 功能描述: 簡單sql字段解析器
*
* 樣例如1:
* select COALESCE(t1.xno, t2.xno, t3.xno) as xno,
* case when t1.no is not null then 1 else null end as xxk001,
* case when t2.no is not null then 1 else null end as xxk200,
* case when t3.xno is not null then 1 else null end as xx3200
* from xxk001 t1
* full join xxkj100 t2 on t1.xno = t2.xno
* full join xxkj200 t3 on t1.xno = t3.xno;
*
* 樣例如2:
* select cast(a as string) as b from ccc;
*
* 樣例如3:
* with a as(select cus,x1 from b1), b as (select cus,x2 from b2)
* select a.cus as a_cus from a join b on a.cus=b.cus where xxx;
*
* 樣例如4:
* select a.xno,b.xx from a_tb as a join b_tb as b on a.id = b.id
*
* 樣例如5:
* select cast \t(a as string) a_str, cc (a as double) a_double from x
*
*/
public class SimpleSqlFieldParser {
/**
* 解析一段次標(biāo)簽sql 中的字段列表
*
* @param sql 原始sql, 需如 select xx from xxx join ... 格式
* @return 字段列表
*/
public static ListSelectFieldClauseDescriptor> parse(String sql) {
String columnPart = adaptFieldPartSql(sql);
int deep = 0;
ListStringBuilder> fieldTokenSwap = new ArrayList>();
StringBuilder currentTokenBuilder = new StringBuilder();
ListSelectFieldClauseDescriptor> fieldList = new ArrayList>();
fieldTokenSwap.add(currentTokenBuilder);
int len = columnPart.length();
char[] columnPartChars = columnPart.toCharArray();
for(int i = 0; i len; i++) {
// 空格忽略，換行忽略，tab忽略
// 字符串相接
// 左(號(hào)入棧，++deep；
// 右)號(hào)出棧，--deep；
// deep>0 忽略所有其他直接拼接
// as 則取下一個(gè)值為fieldName
// case 則直接取到end為止；
//,號(hào)則重置token，構(gòu)建結(jié)果集
char currentChar = columnPartChars[i];
switch (currentChar) {
case '(':
++deep;
currentTokenBuilder.append(currentChar);
break;
case ')':
--deep;
currentTokenBuilder.append(currentChar);
break;
case ',':
if(deep == 0) {
addNewField(fieldList, fieldTokenSwap, true);
fieldTokenSwap = new ArrayList>();
currentTokenBuilder = new StringBuilder();
fieldTokenSwap.add(currentTokenBuilder);
break;
}
currentTokenBuilder.append(currentChar);
break;
case ' ':
case '\t':
case '\r':
case '\n':
if(deep > 0) {
currentTokenBuilder.append(currentChar);
continue;
}
if(currentTokenBuilder.length() == 0) {
continue;
}
// original_name as --> alias
if(i + 1 len) {
int j = i + 1;
// 收集連續(xù)的空格
StringBuilder spaceHolder = new StringBuilder();
boolean isNextLeftBracket = false;
do {
char nextChar = columnPart.charAt(j++);
if(nextChar == ' ' || nextChar == '\t'
|| nextChar == '\r' || nextChar == '\n') {
spaceHolder.append(nextChar);
continue;
}
if(nextChar == '(') {
isNextLeftBracket = true;
}
break;
} while (j len);
if(isNextLeftBracket) {
currentTokenBuilder.append(currentChar);
}
if(spaceHolder.length() > 0) {
currentTokenBuilder.append(spaceHolder);
i += spaceHolder.length();
}
if(isNextLeftBracket) {
// continue next for, function begin
continue;
}
}
if(fieldTokenSwap.size() == 1) {
if(fieldTokenSwap.get(0).toString().equalsIgnoreCase("case")) {
String caseWhenPart = CommonUtil.readSplitWord(
columnPartChars, i, " ", "end");
currentTokenBuilder.append(caseWhenPart);
if(caseWhenPart.length() = 0) {
throw new BizException("語法錯(cuò)誤，未找到case..when的結(jié)束符");
}
i += caseWhenPart.length();
}
}
addNewField(fieldList, fieldTokenSwap, false);
currentTokenBuilder = new StringBuilder();
fieldTokenSwap.add(currentTokenBuilder);
break;
// 空格忽略
default:
currentTokenBuilder.append(currentChar);
break;
}
}
// 處理剩余尚未存儲(chǔ)的字段信息
addNewField(fieldList, fieldTokenSwap, true);
return fieldList;
}
/**
* 新增一個(gè)字段描述
*
* @param fieldList 字段容器
* @param fieldTokenSwap 候選詞
*/
private static void addNewField(ListSelectFieldClauseDescriptor> fieldList,
ListStringBuilder> fieldTokenSwap,
boolean forceAdd) {
int ts = fieldTokenSwap.size();
if(ts == 1 forceAdd) {
// db.original_name,
String fieldName = fieldTokenSwap.get(0).toString();
String alias = fieldName;
if(fieldName.contains(".")) {
alias = fieldName.substring(fieldName.lastIndexOf('.') + 1);
}
fieldList.add(new SelectFieldClauseDescriptor(fieldName, alias));
return;
}
if(ts 2) {
return;
}
if(ts == 2) {
// original_name alias,
if(fieldTokenSwap.get(1).toString().equalsIgnoreCase("as")) {
return;
}
fieldList.add(new SelectFieldClauseDescriptor(
fieldTokenSwap.get(0).toString(),
fieldTokenSwap.get(1).toString()));
}
else if(ts == 3) {
// original_name as alias,
fieldList.add(new SelectFieldClauseDescriptor(
fieldTokenSwap.get(0).toString(),
fieldTokenSwap.get(2).toString()));
}
else {
throw new BizException("字段語法解析錯(cuò)誤，超過3個(gè)以字段描述信息:" + ts);
}
}
// 截取適配 field 字段信息部分
private static String adaptFieldPartSql(String fullSql) {
int start = fullSql.lastIndexOf("select ");
int end = fullSql.lastIndexOf(" from");
String columnPart = fullSql.substring(start + "select ".length(), end);
return columnPart.trim();
}
}
應(yīng)該說是比較簡單的，一個(gè)for, 一個(gè) switch ，就搞定了。其他的，更多的是邏輯判定。
下面我們來看看字段描述類的寫法，其實(shí)就是兩個(gè)字段，源字段和別名。
/**
* 功能描述: sql字段描述 select 字段描述類
*
*/
public class SelectFieldClauseDescriptor {
private String fieldName;
private String alias;
public SelectFieldClauseDescriptor(String fieldName, String alias) {
this.fieldName = fieldName;
this.alias = alias;
}
public String getFieldName() {
return fieldName;
}
public String getAlias() {
return alias;
}
@Override
public boolean equals(Object o) {
if (this == o) return true;
if (o == null || getClass() != o.getClass()) return false;
SelectFieldClauseDescriptor that = (SelectFieldClauseDescriptor) o;
return Objects.equals(fieldName, that.fieldName)
Objects.equals(alias, that.alias);
}
@Override
public int hashCode() {
return Objects.hash(fieldName, alias);
}
@Override
public String toString() {
return "SelectFieldClauseDescriptor{" +
"fieldName='" + fieldName + '\'' +
", alias='" + alias + ''' +
'}';
}
}
它存在的意義，僅僅是為了使用方更方便取值，以為更進(jìn)一步的解析提供了依據(jù)。
3. 單元測試
其實(shí)像寫這種工具類，單元測試最是方便簡單。因?yàn)樽畛醯慕Y(jié)果，我們?cè)缫杨A(yù)料，以測試驅(qū)動(dòng)開發(fā)最合適不過了。而且，基本上一出現(xiàn)不符合預(yù)期的值時(shí)，很快速就定位問題了。
/**
* 功能描述: sql字段解析器測試
**/
public class SimpleSqlFieldParserTest {
@Test
public void testParse() {
String sql;
ListSelectFieldClauseDescriptor> parsedFieldList;
sql = "select COALESCE(t1.xno, t2.xno, t3.xno) as xno,\n" +
" case when t1.xno is not null then 1 else null end as xxk001,\n" +
" case when t2.xno is not null then 1 else null end as xxk200,\n" +
" case when t3.xno is not null then 1 else null end as xx3200\n" +
" from xxk001 t1\n" +
" full join xxkj100 t2 on t1.xno = t2.xno\n" +
" full join xxkj200 t3 on t1.xno = t3.xno;";
parsedFieldList = SimpleSqlFieldParser.parse(sql);
System.out.println("result:");
parsedFieldList.forEach(System.out::println);
Assert.assertEquals("字段個(gè)數(shù)解析不正確",
4, parsedFieldList.size());
Assert.assertEquals("字段別名解析不正確",
"xno", parsedFieldList.get(0).getAlias());
Assert.assertEquals("字段別名解析不正確",
"xx3200", parsedFieldList.get(3).getAlias());
sql = "select cast(a as string) as b from ccc;";
parsedFieldList = SimpleSqlFieldParser.parse(sql);
System.out.println("result:");
parsedFieldList.forEach(System.out::println);
Assert.assertEquals("字段個(gè)數(shù)解析不正確",
1, parsedFieldList.size());
Assert.assertEquals("字段別名解析不正確",
"b", parsedFieldList.get(0).getAlias());
sql = "with a as(select cus,x1 from b1), b as (select cus,x2 from b2)\n" +
" select a.cus as a_cus, cast(a \nas string) as a_cus2, " +
"b.x2 b2 from a join b on a.cus=b.cus where xxx;";
parsedFieldList = SimpleSqlFieldParser.parse(sql);
System.out.println("result:");
parsedFieldList.forEach(System.out::println);
Assert.assertEquals("字段個(gè)數(shù)解析不正確",
3, parsedFieldList.size());
Assert.assertEquals("字段別名解析不正確",
"a_cus", parsedFieldList.get(0).getAlias());
Assert.assertEquals("字段別名解析不正確",
"b2", parsedFieldList.get(2).getAlias());
sql = "select a.xno,b.xx,qqq from a_tb as a join b_tb as b on a.id = b.id";
parsedFieldList = SimpleSqlFieldParser.parse(sql);
System.out.println("result:");
parsedFieldList.forEach(System.out::println);
Assert.assertEquals("字段個(gè)數(shù)解析不正確",
3, parsedFieldList.size());
Assert.assertEquals("字段別名解析不正確",
"xno", parsedFieldList.get(0).getAlias());
Assert.assertEquals("字段別名解析不正確",
"qqq", parsedFieldList.get(2).getAlias());
sql = "select cast (a.a_int as string) a_str, b.xx, coalesce \n( a, b, c) qqq from a_tb as a join b_tb as b on a.id = b.id";
parsedFieldList = SimpleSqlFieldParser.parse(sql);
System.out.println("result:");
parsedFieldList.forEach(System.out::println);
Assert.assertEquals("字段個(gè)數(shù)解析不正確",
3, parsedFieldList.size());
Assert.assertEquals("字段別名解析不正確",
"a_str", parsedFieldList.get(0).getAlias());
Assert.assertEquals("字段原始名解析不正確",
"cast (a.a_int as string)", parsedFieldList.get(0).getFieldName());
Assert.assertEquals("字段別名解析不正確",
"qqq", parsedFieldList.get(2).getAlias());
Assert.assertEquals("字段原始名解析不正確",
"coalesce \n( a, b, c)", parsedFieldList.get(2).getFieldName());
}
}
至此，一個(gè)簡單的字段解析器完成。小工具，供參考！
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