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前言
前面的文章介紹了mybatis核心配置檔案和mapper檔案的解析,之後因為加班比較重,加上個人也比較懶,一拖就是将近半個月,今天抽空開始第二部分的閱讀。
由前面的文章可知,mapper檔案中定義的Sql節點會被解析成MappedStatement,其中的SQL語句會被解析成SqlSource。而Sql語句中定義的動态sql節點(如if節點、foreach節點)會被解析成SqlNode。SqlNode節點的解析中會使用到Ognl表達式(沒錯就是是struts2用的那玩意。本以為随着struts2和jsp淡出開發環境,這種動态标簽也會随之過時,沒想到mybatis裡依然沿用了ognl),這個内容介紹起來有點麻煩,是以感興趣的讀者請自行了解一下。
SqlSource
Sql節點中的Sql語句會被解析成SqlSource,SqlSource接口中隻定義了一個方法 getBoundSql 。該方法用于表示解析後的Sql語句(帶問号)。
public interface SqlSource {
BoundSql getBoundSql(Object parameterObject);
}
[點選并拖拽以移動]
SqlSource的繼承關系如下圖所示。每個實作類都比較簡單,下面隻做簡單的說明。
DynamicSqlSource用于處理動态語句(帶有動态sql标簽),RawSqlSource用于處理靜态語句(沒有動态sql标簽),二者最終會解析成StaticSqlSource。StaticSqlSource可能會帶有問号。這裡暫時隻将代碼簡單的貼出來,部分内容需要結合後面才可以加注釋(如SqlNode)
public class RawSqlSource implements SqlSource {
private final SqlSource sqlSource;
public RawSqlSource(Configuration configuration, SqlNode rootSqlNode, Class<?> parameterType) {
this(configuration, getSql(configuration, rootSqlNode), parameterType);
}
public RawSqlSource(Configuration configuration, String sql, Class<?> parameterType) {
SqlSourceBuilder sqlSourceParser = new SqlSourceBuilder(configuration);
Class<?> clazz = parameterType == null ? Object.class : parameterType;
sqlSource = sqlSourceParser.parse(sql, clazz, new HashMap<>());
}
private static String getSql(Configuration configuration, SqlNode rootSqlNode) {
DynamicContext context = new DynamicContext(configuration, null);
rootSqlNode.apply(context);
return context.getSql();
}
@Override
public BoundSql getBoundSql(Object parameterObject) {
return sqlSource.getBoundSql(parameterObject);
}
}
public class DynamicSqlSource implements SqlSource {
private final Configuration configuration;
private final SqlNode rootSqlNode;
public DynamicSqlSource(Configuration configuration, SqlNode rootSqlNode) {
this.configuration = configuration;
this.rootSqlNode = rootSqlNode;
}
@Override
public BoundSql getBoundSql(Object parameterObject) {
DynamicContext context = new DynamicContext(configuration, parameterObject);
rootSqlNode.apply(context);
SqlSourceBuilder sqlSourceParser = new SqlSourceBuilder(configuration);
Class<?> parameterType = parameterObject == null ? Object.class : parameterObject.getClass();
SqlSource sqlSource = sqlSourceParser.parse(context.getSql(), parameterType, context.getBindings());
BoundSql boundSql = sqlSource.getBoundSql(parameterObject);
context.getBindings().forEach(boundSql::setAdditionalParameter);
return boundSql;
}
}
public class StaticSqlSource implements SqlSource {
private final String sql;
private final List parameterMappings;
private final Configuration configuration;
public StaticSqlSource(Configuration configuration, String sql) {
this(configuration, sql, null);
}
public StaticSqlSource(Configuration configuration, String sql, List parameterMappings) {
this.sql = sql;
this.parameterMappings = parameterMappings;
this.configuration = configuration;
}
@Override
public BoundSql getBoundSql(Object parameterObject) {
return new BoundSql(configuration, sql, parameterMappings, parameterObject);
}
}
ProviderSqlSource暫時不貼出來(還沒讀到這裡)
DynamicContext
DynamicContext用于記錄解析動态Sql時産生的Sql片段。這裡也先将主要代碼放出來。
public class DynamicContext {
public static final String PARAMETER_OBJECT_KEY = “_parameter”;
public static final String DATABASE_ID_KEY = “_databaseId”;
static {
OgnlRuntime.setPropertyAccessor(ContextMap.class, new ContextAccessor());
}
private final StringJoiner sqlBuilder = new StringJoiner(" ");
private int uniqueNumber = 0;
public DynamicContext(Configuration configuration, Object parameterObject) {
if (parameterObject != null && !(parameterObject instanceof Map)) {
// 非Map就去找對應的類型處理器
MetaObject metaObject = configuration.newMetaObject(parameterObject);
boolean existsTypeHandler = configuration.getTypeHandlerRegistry().hasTypeHandler(parameterObject.getClass());
bindings = new ContextMap(metaObject, existsTypeHandler);
} else {
bindings = new ContextMap(null, false);
}
bindings.put(PARAMETER_OBJECT_KEY, parameterObject);
bindings.put(DATABASE_ID_KEY, configuration.getDatabaseId());
}
public Map<String, Object> getBindings() {
return bindings;
}
public void bind(String name, Object value) {
bindings.put(name, value);
}
public void appendSql(String sql) {
sqlBuilder.add(sql);
}
public String getSql() {
return sqlBuilder.toString().trim();
}
public int getUniqueNumber() {
return uniqueNumber++;
}
}
SqlNode
SqlNode表示Sql節點中的動态Sql。該類(接口)隻有一個apply方法,用于解析動态Sql節點,并調用DynamicContext的appendSql方法去拼接sql語句。
public interface SqlNode {
boolean apply(DynamicContext context);
}
SqlNode實作類很多,如圖所示。光看實作類的名稱,想必大家都可以猜出這些實作類的作用了。下面将對這些實作類一一解釋
StaticTextSqlNode使用text字段記錄非動态Sql節點,apply方法直接将text字段追加到DynamicContext.sqlBuilder;MixedSqlNode中使用contents字段存放子節點的動态sql,apply方法則是周遊contents去調用每個SqlNode的apply方法,代碼都比較簡單就不貼出來了。
TextSqlNode
TextSqlNode表示包含 的 s q l 節 點 , i s D y n a m i c 方 法 用 于 檢 測 s q l 中 是 否 包 含 {}的sql節點,isDynamic方法用于檢測sql中是否包含 的sql節點,isDynamic方法用于檢測sql中是否包含{}占位符。該類的apply方法會使用GenericTokenParser将 占 位 符 解 析 成 實 際 意 義 的 參 數 值 , 因 此 {}占位符解析成實際意義的參數值,是以 占位符解析成實際意義的參數值,是以{}在mybatis中會有注入風險,應當慎用,盡量用于非前端傳遞的參數。這裡比較特殊的場景就是order by。order by後面隻能使用${}占位符,是以前端操作排序列時,務必要做防注入處理。
public class TextSqlNode implements SqlNode {
private final String text;
private final Pattern injectionFilter;
public TextSqlNode(String text) {
this(text, null);
}
public TextSqlNode(String text, Pattern injectionFilter) {
this.text = text;
this.injectionFilter = injectionFilter;
}
public boolean isDynamic() {
DynamicCheckerTokenParser checker = new DynamicCheckerTokenParser();
GenericTokenParser parser = createParser(checker);
parser.parse(text);
return checker.isDynamic();
}
@Override
public boolean apply(DynamicContext context) {
GenericTokenParser parser = createParser(new BindingTokenParser(context, injectionFilter));
context.appendSql(parser.parse(text));
return true;
}
private GenericTokenParser createParser(TokenHandler handler) {
// 這裡辨別解析的是 占 位 符 r e t u r n n e w G e n e r i c T o k e n P a r s e r ( " {}占位符 return new GenericTokenParser(" 占位符returnnewGenericTokenParser("{", “}”, handler);
}
private static class BindingTokenParser implements TokenHandler {
private DynamicContext context;
private Pattern injectionFilter;
public BindingTokenParser(DynamicContext context, Pattern injectionFilter) {
this.context = context;
this.injectionFilter = injectionFilter;
}
@Override
public String handleToken(String content) {
// 擷取使用者提供的實參
Object parameter = context.getBindings().get("_parameter");
if (parameter == null) {
context.getBindings().put("value", null);
} else if (SimpleTypeRegistry.isSimpleType(parameter.getClass())) {
context.getBindings().put("value", parameter);
}
// 通過ognl解析content的值
Object value = OgnlCache.getValue(content, context.getBindings());
String srtValue = value == null ? "" : String.valueOf(value); // issue #274 return "" instead of "null"
checkInjection(srtValue);
return srtValue;
}
private void checkInjection(String value) {
if (injectionFilter != null && !injectionFilter.matcher(value).matches()) {
throw new ScriptingException("Invalid input. Please conform to regex" + injectionFilter.pattern());
}
}
}
private static class DynamicCheckerTokenParser implements TokenHandler {
private boolean isDynamic;
public DynamicCheckerTokenParser() {
// Prevent Synthetic Access
}
public boolean isDynamic() {
return isDynamic;
}
@Override
public String handleToken(String content) {
this.isDynamic = true;
return null;
}
}
}
IfSqlNode
該類表示mybatis中的if标簽。if标簽中使用的其實就是Ognl語句,是以可以有一些很花哨的寫法,如調用參數的equals方法等,這裡不對Ognl表達式做過多的介紹。
private final SqlNode contents;
public IfSqlNode(SqlNode contents, String test) {
this.test = test;
this.contents = contents;
this.evaluator = new ExpressionEvaluator();
}
@Override
public boolean apply(DynamicContext context) {
// 檢測表達式是否為true,來決定是否執行apply方法
if (evaluator.evaluateBoolean(test, context.getBindings())) {
contents.apply(context);
return true;
}
return false;
}
}
TrimSqlNode
trimSqlNode用于根據解析結果添加或删除字尾活字首。
public class TrimSqlNode implements SqlNode {
private final List suffixesToOverride;
private final Configuration configuration;
public TrimSqlNode(Configuration configuration, SqlNode contents, String prefix, String prefixesToOverride, String suffix, String suffixesToOverride) {
this(configuration, contents, prefix, parseOverrides(prefixesToOverride), suffix, parseOverrides(suffixesToOverride));
}
protected TrimSqlNode(Configuration configuration, SqlNode contents, String prefix, List prefixesToOverride, String suffix, List suffixesToOverride) {
this.contents = contents;
this.prefix = prefix;
this.prefixesToOverride = prefixesToOverride;
this.suffix = suffix;
this.suffixesToOverride = suffixesToOverride;
this.configuration = configuration;
}
@Override
public boolean apply(DynamicContext context) {
FilteredDynamicContext filteredDynamicContext = new FilteredDynamicContext(context);
boolean result = contents.apply(filteredDynamicContext);
// 處理字首和字尾
filteredDynamicContext.applyAll();
return result;
}
private static List parseOverrides(String overrides) {
if (overrides != null) {
// 使用|分隔
final StringTokenizer parser = new StringTokenizer(overrides, “|”, false);
final List list = new ArrayList<>(parser.countTokens());
while (parser.hasMoreTokens()) {
list.add(parser.nextToken().toUpperCase(Locale.ENGLISH));
}
return list;
}
return Collections.emptyList();
}
private class FilteredDynamicContext extends DynamicContext {
private StringBuilder sqlBuffer;
public FilteredDynamicContext(DynamicContext delegate) {
super(configuration, null);
this.delegate = delegate;
this.prefixApplied = false;
this.suffixApplied = false;
this.sqlBuffer = new StringBuilder();
}
public void applyAll() {
sqlBuffer = new StringBuilder(sqlBuffer.toString().trim());
String trimmedUppercaseSql = sqlBuffer.toString().toUpperCase(Locale.ENGLISH);
if (trimmedUppercaseSql.length() > 0) {
applyPrefix(sqlBuffer, trimmedUppercaseSql);
applySuffix(sqlBuffer, trimmedUppercaseSql);
}
delegate.appendSql(sqlBuffer.toString());
}
@Override
public Map<String, Object> getBindings() {
return delegate.getBindings();
}
@Override
public void bind(String name, Object value) {
delegate.bind(name, value);
}
@Override
public int getUniqueNumber() {
return delegate.getUniqueNumber();
}
@Override
public void appendSql(String sql) {
sqlBuffer.append(sql);
}
@Override
public String getSql() {
return delegate.getSql();
}
/**
* 處理字首
*
* @param sql sql
* @param trimmedUppercaseSql 小寫sql
*/
private void applyPrefix(StringBuilder sql, String trimmedUppercaseSql) {
if (!prefixApplied) {
prefixApplied = true;
if (prefixesToOverride != null) {
for (String toRemove : prefixesToOverride) {
// 周遊prefixesToOverride,如果以其中的某項開頭就從SQL語句開頭剔除
if (trimmedUppercaseSql.startsWith(toRemove)) {
sql.delete(0, toRemove.trim().length());
break;
}
}
}
if (prefix != null) {
sql.insert(0, " ");
sql.insert(0, prefix);
}
}
}
/**
* 處理字尾。
* @param sql
* @param trimmedUppercaseSql
*/
private void applySuffix(StringBuilder sql, String trimmedUppercaseSql) {
if (!suffixApplied) {
suffixApplied = true;
if (suffixesToOverride != null) {
for (String toRemove : suffixesToOverride) {
if (trimmedUppercaseSql.endsWith(toRemove) || trimmedUppercaseSql.endsWith(toRemove.trim())) {
int start = sql.length() - toRemove.trim().length();
int end = sql.length();
sql.delete(start, end);
break;
}
}
}
if (suffix != null) {
sql.append(" ");
sql.append(suffix);
}
}
}
}
}
WhereSqlNode&SetSqlNode
WhereSqlNode和SetSqlNode分别表示where節點和set節點。這兩個類繼承了TrimSqlNode,是以自帶處理前字尾的功能。
WhereSqlNode将and、or兩個關鍵字作為需要删除的字首。當where的第一個條件以這兩個開頭時,會将and或者or删除。而SetSqlNode則會删除字首或者字尾的嘤文逗号。這裡隻貼出WhereSqlNode代碼。
public class WhereSqlNode extends TrimSqlNode {
private static List prefixList = Arrays.asList("AND ", "OR ", “AND\n”, “OR\n”, “AND\r”, “OR\r”, “AND\t”, “OR\t”);
public WhereSqlNode(Configuration configuration, SqlNode contents) {
super(configuration, contents, “WHERE”, prefixList, null, null);
}
}
ForeachSqlNode
在動态Sql語句中建構in條件時,往往需要周遊一個集合,是以使用foreach标簽。這裡需要着重介紹一下FilteredDynamicContext這個内部類。該類繼承了DynamicContext,用來處理foreach中的#{}占位符。這裡是對其不完全的處理。如#{item}會被處理乘#{__frch_item_index值}這種格式,用來表示周遊中的每一項。
public class ForEachSqlNode implements SqlNode {
public static final String ITEM_PREFIX = “_frch”;
private final String index;
private final Configuration configuration;
public ForEachSqlNode(Configuration configuration, SqlNode contents, String collectionExpression, String index, String item, String open, String close, String separator) {
this.evaluator = new ExpressionEvaluator();
this.collectionExpression = collectionExpression;
this.contents = contents;
this.open = open;
this.close = close;
this.separator = separator;
this.index = index;
this.item = item;
this.configuration = configuration;
}
@Override
public boolean apply(DynamicContext context) {
Map<String, Object> bindings = context.getBindings();
final Iterable<?> iterable = evaluator.evaluateIterable(collectionExpression, bindings);
if (!iterable.iterator().hasNext()) {
return true;
}
boolean first = true;
// 循環之前添加open指定的字元串
applyOpen(context);
int i = 0;
for (Object o : iterable) {
DynamicContext oldContext = context;
if (first || separator == null) {
// 是第一個循環,并且沒有間隔符
context = new PrefixedContext(context, “”);
} else {
context = new PrefixedContext(context, separator);
}
int uniqueNumber = context.getUniqueNumber();
// 将index和item添加到DynamicContext.bindings集合
if (o instanceof Map.Entry) {
@SuppressWarnings(“unchecked”)
Map.Entry<Object, Object> mapEntry = (Map.Entry<Object, Object>) o;
applyIndex(context, mapEntry.getKey(), uniqueNumber);
applyItem(context, mapEntry.getValue(), uniqueNumber);
} else {
applyIndex(context, i, uniqueNumber);
applyItem(context, o, uniqueNumber);
}
// 調用子節點的apply急需處理
contents.apply(new FilteredDynamicContext(configuration, context, index, item, uniqueNumber));
if (first) {
first = !((PrefixedContext) context).isPrefixApplied();
}
context = oldContext;
i++;
}
// 拼接close
applyClose(context);
context.getBindings().remove(item);
context.getBindings().remove(index);
return true;
}
private void applyIndex(DynamicContext context, Object o, int i) {
if (index != null) {
context.bind(index, o);
context.bind(itemizeItem(index, i), o);
}
}
private void applyItem(DynamicContext context, Object o, int i) {
if (item != null) {
context.bind(item, o);
context.bind(itemizeItem(item, i), o);
}
}
private void applyOpen(DynamicContext context) {
if (open != null) {
context.appendSql(open);
}
}
private void applyClose(DynamicContext context) {
if (close != null) {
context.appendSql(close);
}
}
private static String itemizeItem(String item, int i) {
return ITEM_PREFIX + item + “_” + i;
}
private static class FilteredDynamicContext extends DynamicContext {
private final DynamicContext delegate;
private final int index;
private final String itemIndex;
private final String item;
public FilteredDynamicContext(Configuration configuration, DynamicContext delegate, String itemIndex, String item, int i) {
super(configuration, null);
this.delegate = delegate;
this.index = i;
this.itemIndex = itemIndex;
this.item = item;
}
@Override
public Map<String, Object> getBindings() {
return delegate.getBindings();
}
@Override
public void bind(String name, Object value) {
delegate.bind(name, value);
}
@Override
public String getSql() {
return delegate.getSql();
}
/**
- 這裡會将#{item}占位符解析成#{__frch_item_index值}
-
@param sql
/
@Override
public void appendSql(String sql) {
GenericTokenParser parser = new GenericTokenParser("#{", “}”, content -> {
String newContent = content.replaceFirst("^\s" + item + “(?![^.,:\s])”, itemizeItem(item, index));
if (itemIndex != null && newContent.equals(content)) {
newContent = content.replaceFirst("^\s*" + itemIndex + “(?![^.,:\s])”, itemizeItem(itemIndex, index));
}
return “#{” + newContent + “}”;
});
delegate.appendSql(parser.parse(sql));
}
@Override
public int getUniqueNumber() {
return delegate.getUniqueNumber();
}
}
private class PrefixedContext extends DynamicContext {
private final DynamicContext delegate;
private final String prefix;
private boolean prefixApplied;
public PrefixedContext(DynamicContext delegate, String prefix) {
super(configuration, null);
this.delegate = delegate;
this.prefix = prefix;
this.prefixApplied = false;
}
public boolean isPrefixApplied() {
return prefixApplied;
}
@Override
public Map<String, Object> getBindings() {
return delegate.getBindings();
}
@Override
public void bind(String name, Object value) {
delegate.bind(name, value);
}
@Override
public void appendSql(String sql) {
if (!prefixApplied && sql != null && sql.trim().length() > 0) {
delegate.appendSql(prefix);
prefixApplied = true;
}
delegate.appendSql(sql);
}
@Override
public String getSql() {
return delegate.getSql();
}
@Override
public int getUniqueNumber() {
return delegate.getUniqueNumber();
}
}
}
剩餘的如ChooseSqlNode請讀者自行閱讀,代碼也都比較容易了解。
結語
本次文章隻是介紹一下動态sql解析時常用的類和接口,之後的文章對動态sql進行介紹時将不再對這些類進行贅述。
最後說一些閑話。
其實堅持寫部落格是一件很難的事情。七月份入職以來,便開始考慮寫部落格的事,起初不知道從哪寫起,部落格品質并不高。後來慢慢愛上了閱讀源碼這件事。其實mybatis源碼我已經參照某本書讀完了,但是閱讀完之後我并沒有覺得有何收獲和見解,對源碼的了解也比較淺顯,是以便想着通過撰寫部落格的方式去加深對源碼的認知。Mybatis插件機制是很重要的特性,而想編寫一個好的插件就需要對源碼有深刻的了解,是以源碼不得不讀,對于一個java程式員來說這也是必修課。在這幾篇部落格的撰寫下,我慢慢養成了寫部落格的習慣,也知道什麼該寫,什麼不該寫。部落格中大部分的内容其實都在代碼注釋上,是以顯得部落格内容不多,需要閱讀者仔細閱讀代碼注釋(但願我的部落格有人看吧。)。養成一個習慣不容易,這段時間劃水的過程中對撰寫部落格這件事也有所懈怠(說實話差點都忘了我還開了這麼大一個坑。)
*************************************優雅的分割線 **********************************
分享一波:程式員賺外快-必看的巅峰幹貨
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