MyBatis源码学习（四）

private final String sql;
private final List<ParameterMapping> parameterMappings;
private final Object parameterObject;
private final Map<String, Object> additionalParameters;
private final MetaObject metaParameters;
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// -☆- MappedStatement
public BoundSql getBoundSql(Object parameterObject) {
// 调用 sqlSource 的 getBoundSql 获取 BoundSql
BoundSql boundSql = sqlSource.getBoundSql(parameterObject);
List<ParameterMapping> parameterMappings =
boundSql.getParameterMappings();
if (parameterMappings == null || parameterMappings.isEmpty()) {
// 创建新的 BoundSql，这里的 parameterMap 是 ParameterMap 类型。
// 由<ParameterMap> 节点进行配置，该节点已经废弃，不推荐使用。
// 默认情况下，parameterMap.getParameterMappings() 返回空集合
boundSql = new BoundSql(configuration, boundSql.getSql(), 
parameterMap.getParameterMappings(), parameterObject);
 }
// 省略不重要的逻辑
return boundSql; }
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// -☆- DynamicSqlSource
public BoundSql getBoundSql(Object parameterObject) {
// 创建 DynamicContext
DynamicContext context =
new DynamicContext(configuration, parameterObject);
// 解析 SQL 片段，并将解析结果存储到 DynamicContext 中
rootSqlNode.apply(context);
SqlSourceBuilder sqlSourceParser = new SqlSourceBuilder(configuration);
Class<?> parameterType = parameterObject == null ?
Object.class : parameterObject.getClass();
// 构建 StaticSqlSource，在此过程中将 sql 语句中的占位符 #{} 替换为问号 ?，
// 并为每个占位符构建相应的 ParameterMapping
SqlSource sqlSource = sqlSourceParser.parse(
context.getSql(), parameterType, context.getBindings());
// 调用 StaticSqlSource 的 getBoundSql 获取 BoundSql
BoundSql boundSql = sqlSource.getBoundSql(parameterObject);
// 将 DynamicContext 的 ContextMap 中的内容拷贝到 BoundSql 中
for(Map.Entry<String, Object> entry : context.getBindings().entrySet()){
boundSql.setAdditionalParameter(entry.getKey(), entry.getValue());
 }
return boundSql; }
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public class DynamicContext {
public static final String PARAMETER_OBJECT_KEY = "_parameter";
public static final String DATABASE_ID_KEY = "_databaseId";
private final ContextMap bindings;
private final StringBuilder sqlBuilder = new StringBuilder();
public DynamicContext(
Configuration configuration, Object parameterObject) {
// 创建 ContextMap
if (parameterObject != null && !(parameterObject instanceof Map)) {
MetaObject metaObject =
configuration.newMetaObject(parameterObject);
bindings = new ContextMap(metaObject);
 } else {
bindings = new ContextMap(null);
 }
// 存放运行时参数 parameterObject 以及 databaseId
bindings.put(PARAMETER_OBJECT_KEY, parameterObject);
bindings.put(DATABASE_ID_KEY, configuration.getDatabaseId());
 } }
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public class MixedSqlNode implements SqlNode {
private final List<SqlNode> contents;
public MixedSqlNode(List<SqlNode> contents) {
this.contents = contents;
 }
 @Override
public boolean apply(DynamicContext context) {
// 遍历 SqlNode 集合
for (SqlNode sqlNode : contents) {
// 调用 salNode 对象本身的 apply 方法解析 sql
sqlNode.apply(context);
 }
return true;
 } }
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public class StaticTextSqlNode implements SqlNode {
private final String text;
public StaticTextSqlNode(String text) {
this.text = text;
 }
@Override
public boolean apply(DynamicContext context) {
context.appendSql(text);
return true;
 } }
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public class TextSqlNode implements SqlNode {
private final String text;
private final Pattern injectionFilter;
@Override
public boolean apply(DynamicContext context) {
// 创建 ${} 占位符解析器
GenericTokenParser parser = createParser(
new BindingTokenParser(context, injectionFilter));
// 解析 ${} 占位符，并将解析结果添加到 DynamicContext 中
context.appendSql(parser.parse(text));
return true;
 }
private GenericTokenParser createParser(TokenHandler handler) {
// 创建占位符解析器，GenericTokenParser 是一个通用解析器，
// 并非只能解析 ${} 占位符
return new GenericTokenParser("${", "}", 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) {
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);
 }
// 通过 ONGL 从用户传入的参数中获取结果
Object value = OgnlCache
.getValue(content, context.getBindings());
String srtValue = (value == null ? "" : String.valueOf(value));
// 通过正则表达式检测 srtValue 有效性
checkInjection(srtValue);
return srtValue;
 }
 } }
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public class IfSqlNode implements SqlNode {
private final ExpressionEvaluator evaluator;
private final String test;
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) {
// 通过 ONGL 评估 test 表达式的结果
if (evaluator.evaluateBoolean(test, context.getBindings())) {
// 若 test 表达式中的条件成立，则调用其他节点的 apply 方法进行解析
contents.apply(context);
return true;
 }
return false;
 } }
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public class WhereSqlNode extends TrimSqlNode {
/** 前缀列表 */
private static List<String> prefixList = Arrays.asList(
"AND ", "OR ", "AND\n", "OR\n", "AND\r", "OR\r", "AND\t", "OR\t");
public WhereSqlNode(Configuration configuration, SqlNode contents) {
// 调用父类的构造方法
super(configuration, contents, "WHERE", prefixList, null, null);
 } }
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public class TrimSqlNode implements SqlNode {
private final SqlNode contents;
private final String prefix;
private final String suffix;
private final List<String> prefixesToOverride;
private final List<String> suffixesToOverride;
private final Configuration configuration;
@Override
public boolean apply(DynamicContext context) {
// 创建具有过滤功能的 DynamicContext
FilteredDynamicContext filteredDynamicContext =
new FilteredDynamicContext(context);
// 解析节点内容
boolean result = contents.apply(filteredDynamicContext);
// 过滤掉前缀和后缀
filteredDynamicContext.applyAll();
return result;
 } }
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private class FilteredDynamicContext extends DynamicContext {
private DynamicContext delegate;
/** 构造方法会将下面两个布尔值置为 false */
private boolean prefixApplied;
private boolean suffixApplied;
private StringBuilder sqlBuffer;
public void applyAll() {
sqlBuffer = new StringBuilder(sqlBuffer.toString().trim());
String trimmedUppercaseSql =
sqlBuffer.toString().toUpperCase(Locale.ENGLISH);
if (trimmedUppercaseSql.length() > 0) {
// 引用前缀和后缀，也就是对 sql 进行过滤操作，移除掉前缀或后缀
applyPrefix(sqlBuffer, trimmedUppercaseSql);
applySuffix(sqlBuffer, trimmedUppercaseSql);
 }
// 将当前对象的 sqlBuffer 内容添加到代理类中
delegate.appendSql(sqlBuffer.toString());
}
private void applyPrefix(StringBuilder sql, String trimmedUppercaseSql){
if (!prefixApplied) {
// 设置 prefixApplied 为 true，以下逻辑仅会被执行一次
prefixApplied = true;
if (prefixesToOverride != null) {
for (String toRemove : prefixesToOverride) {
// 检测当前 sql 字符串是否包含前缀，比如 'AND ', 'AND\t'等
if (trimmedUppercaseSql.startsWith(toRemove)) {
// 移除前缀
sql.delete(0, toRemove.trim().length());
break;
 }
 }
 }
// 插入前缀，比如 WHERE
if (prefix != null) {
sql.insert(0, " ");
sql.insert(0, prefix);
 }
 }
 }
// 该方法逻辑与 applyPrefix 大同小异，大家自行分析
private void applySuffix(
StringBuilder sql, String trimmedUppercaseSql){
} }
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public class SqlNodeTest {
@Test
public void testWhereSqlNode() throws IOException {
String sqlFragment = "AND id = #{id}";
MixedSqlNode msn = new MixedSqlNode(
Arrays.asList(new StaticTextSqlNode(sqlFragment)));
WhereSqlNode wsn = new WhereSqlNode(new Configuration(), msn);
DynamicContext dc = new DynamicContext(
new Configuration(), new ParamMap<>());
wsn.apply(dc);
System.out.println("解析前：" + sqlFragment);
System.out.println("解析后：" + dc.getSql());
 } }
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