com.ibatis.sqlmap.engine.mapping.sql.dynamic
。ibatis的标签和mybatis的标签之间,区别已经很大了
ibatis在启动的时候,会把所有的sql对象解析出来,并初始化为对应的实际实现。Sql对象的实现类有很多,常见的有
StaticSql,这个是纯净态的,没有动态SQL
DynamicSql是包含了动态标签的SQL对象。
理解了动态SQL其他都是类似原理。
<select id="selectOutSales" resultClass="hashmap"> SELECT t_tz_btscxx.BTSCID, t_tz_btscxx.SZTZDID, t_tz_btscxx.TZSXH, t_tz_btscxx.RTSJ, t_tz_btscxx.RTSL, t_tz_btscxx.SCLXDM, t_tz_btscxx.RTSCX, t_tz_btscxx.ZZL, t_tz_btscxx.SCZT, t_tz_btscxx.SFWCTZ, t_tz_btscxx.WCTZSJ, t_tz_btscxx.CJRY, t_tz_btscxx.CJRQ, t_tz_btscxx.XGRY, t_tz_btscxx.XGRQ, t_tz_btscxx.SCBJ FROM t_tz_btscxx <dynamic prepend="where"> <isNotEmpty prepend="and" property="BTSCID"> BTSCID like '%$BTSCID$%' </isNotEmpty> </dynamic> </select>
如上配置的一个sql语句,第一层节点有三个,text,dynamic元素,text(这个属于XML的知识,具体从XML脑补)。
在调用该SQL的时候,会执行是DynamicSql的
process方法
private void process(StatementScope statementScope, Object parameterObject) { SqlTagContext ctx = new SqlTagContext(); List localChildren = children; processBodyChildren(statementScope, ctx, parameterObject, localChildren.iterator()); ParameterMap map = new ParameterMap(delegate); map.setId(statementScope.getStatement().getId() + "-InlineParameterMap"); map.setParameterClass(((MappedStatement) statementScope.getStatement()).getParameterClass()); map.setParameterMappingList(ctx.getParameterMappings()); String dynSql = ctx.getBodyText(); // Processes $substitutions$ after DynamicSql if (SimpleDynamicSql.isSimpleDynamicSql(dynSql)) { dynSql = new SimpleDynamicSql(delegate, dynSql).getSql(statementScope, parameterObject); } statementScope.setDynamicSql(dynSql); statementScope.setDynamicParameterMap(map); }
比较重要的方法
//这是处理SQL内部各个节点的方法 private void processBodyChildren(StatementScope statementScope, SqlTagContext ctx, Object parameterObject, Iterator localChildren, PrintWriter out) { //每个节点都需要被处理 while (localChildren.hasNext()) { SqlChild child = (SqlChild) localChildren.next(); //纯文本节点,处理比较简单,就是把参数等解析出来。 if (child instanceof SqlText) { SqlText sqlText = (SqlText) child; String sqlStatement = sqlText.getText(); if (sqlText.isWhiteSpace()) { out.print(sqlStatement); } else if (!sqlText.isPostParseRequired()) { // BODY OUT out.print(sqlStatement); ParameterMapping[] mappings = sqlText.getParameterMappings(); if (mappings != null) { for (int i = 0, n = mappings.length; i < n; i++) { ctx.addParameterMapping(mappings[i]); } } } else { IterateContext itCtx = ctx.peekIterateContext(); if(null != itCtx && itCtx.isAllowNext()){ itCtx.next(); itCtx.setAllowNext(false); if(!itCtx.hasNext()) { itCtx.setFinal(true); } } if(itCtx!=null) { StringBuffer sqlStatementBuffer = new StringBuffer(sqlStatement); iteratePropertyReplace(sqlStatementBuffer, itCtx); sqlStatement = sqlStatementBuffer.toString(); } sqlText = PARAM_PARSER.parseInlineParameterMap(delegate.getTypeHandlerFactory(), sqlStatement); ParameterMapping[] mappings = sqlText.getParameterMappings(); out.print(sqlText.getText()); if (mappings != null) { for (int i = 0, n = mappings.length; i < n; i++) { ctx.addParameterMapping(mappings[i]); } } } } else if (child instanceof SqlTag) { //节点本身就是一个节点。每种节点都有自己的显示,每个节点实际上用的是SqlTag,一种Tag的子类。内部包含了SqlTagHandler,每个SqlTag都会初始化自己的处理器。对于dynamic使用的是DynamicTagHandler SqlTag tag = (SqlTag) child; SqlTagHandler handler = tag.getHandler(); int response = SqlTagHandler.INCLUDE_BODY; do { StringWriter sw = new StringWriter(); PrintWriter pw = new PrintWriter(sw); //这句比较重要,对于条件标签,如果条件不满足,会返回SKIP_BODY,来跳过该元素处理 response = handler.doStartFragment(ctx, tag, parameterObject); if (response != SqlTagHandler.SKIP_BODY) { processBodyChildren(statementScope, ctx, parameterObject, tag.getChildren(), pw); pw.flush(); pw.close(); StringBuffer body = sw.getBuffer(); response = handler.doEndFragment(ctx, tag, parameterObject, body); handler.doPrepend(ctx, tag, parameterObject, body); if (response != SqlTagHandler.SKIP_BODY) { if (body.length() > 0) { out.print(body.toString()); } } } } while (response == SqlTagHandler.REPEAT_BODY); ctx.popRemoveFirstPrependMarker(tag); if(ctx.peekIterateContext()!= null && ctx.peekIterateContext().getTag() == tag) { ctx.setAttribute(ctx.peekIterateContext().getTag(), null); ctx.popIterateContext(); } } } }
dynamic元素有三个属性
prepend="where" open="" close=""
prepend和open是在DynamicTagHandler的doStartFragment和doPrepend共同完成处理,close是在doEndFragment处理的。
public class DynamicTagHandler extends BaseTagHandler { public int doStartFragment(SqlTagContext ctx, SqlTag tag, Object parameterObject) { //DynamicTagHandler的doStartFragment只是负责把RemoveFirstPrependMarker标记对象创建和压入。 ctx.pushRemoveFirstPrependMarker(tag); return BaseTagHandler.INCLUDE_BODY; } }
public void pushRemoveFirstPrependMarker(SqlTag tag) { if(tag.getHandler() instanceof DynamicTagHandler) { //对于DynamicTagHandler之类的条件标签,如果开启了prepend属性,需要设置标记为true。这会造成之后的条件语句的改变,即当出现过一个条件满足时,之后的条件的prepend才会有效,而DynamicTagHandler本身的prepend也才会生效。 对于只有条件,而没有对应的上级(select 标签元素等不是上级),只要满足了条件,那么就会追加prepend,而不管具体是不是第一次满足。 // this was added to retain default behavior if(tag.isPrependAvailable()) { removeFirstPrependStack.addFirst( new RemoveFirstPrependMarker(tag,true)); } else { removeFirstPrependStack.addFirst( new RemoveFirstPrependMarker(tag,false)); } } else if("true".equals(tag.getRemoveFirstPrepend()) || "iterate".equals(tag.getRemoveFirstPrepend())){ // you must be specific about the removal otherwise it // will function as ibatis has always functioned and add // the prepend removeFirstPrependStack.addFirst( new RemoveFirstPrependMarker(tag,true)); } else if(!tag.isPrependAvailable() && !"true".equals(tag.getRemoveFirstPrepend()) && !"iterate".equals(tag.getRemoveFirstPrepend()) && tag.getParent() != null) { // if no prepend or removeFirstPrepend is specified // we need to look to the parent tag for default values if("true".equals(tag.getParent().getRemoveFirstPrepend()) || "iterate".equals(tag.getParent().getRemoveFirstPrepend())) { removeFirstPrependStack.addFirst( new RemoveFirstPrependMarker(tag,true)); } } else { removeFirstPrependStack.addFirst( new RemoveFirstPrependMarker(tag,false)); } }
由于dynamic包含了isNotEmpty,因此在dynamic处理之前,需要处理isNotEmpty,
isNotEmpty之前的处理是和dynamic类似的。
isNotEmpty的doPrepend方法是BaseTagHandler的,并没有改写
public void doPrepend(SqlTagContext ctx, SqlTag tag, Object parameterObject, StringBuffer bodyContent) { //可以看到open属性是先于prepend属性处理的。但是每次sql字符插入都是从0位置插入,所以open先处理,但是当open和prepend都存在,prepend会插入到open之前的位置。 if (tag.isOpenAvailable() && !(tag.getHandler() instanceof IterateTagHandler)) { if (bodyContent.toString().trim().length() > 0) { bodyContent.insert(0, tag.getOpenAttr()); } } if (tag.isPrependAvailable()) { if (bodyContent.toString().trim().length() > 0) { //这里看到对于标记是true的,那么第一次不进行追加 //ctx.peekRemoveFirstPrependMarker(tag)取的是堆栈的第二个数据,而不是最顶部的数据。如上的配置,当处理IsNotEmpty的时候,取得是它的父级dynamic的设置。 //实际上ibatis的实现者把父级也看成和子元素一样的的平行级别处理了, P--- C---1 C---2 变成了 C---1 C---2 P--- 的结构,那么当C--1满足,C1不进行住家prepend,而C--2和P--则需要。 if (tag.getParent() != null && ctx.peekRemoveFirstPrependMarker(tag)) { ctx.disableRemoveFirstPrependMarker(); }else { bodyContent.insert(0, tag.getPrependAttr()); } } } }