在上面两节中我们解决了关于NodeHandler和SqlNode的技术债,本章我们继续来还关于SqlSource和ParameterMapping的技术债。
1. SqlSource源码解析
这是一个接口,非常简单,我们来看下源码:
public interface SqlSource {
BoundSql getBoundSql(Object parameterObject);
}
最主要的是我们来看它的子类:
SqlSource子类
在之前我们看过关于RawSqlSource的源码,接下来我们来看下比较难得动态的DynamicSqlSource源码,我们接下来一起展示:
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;
}
}
第一个要注意的就是DynamicContext类,这个类具体是干嘛的呢?我们不进入源码进行分析,如果你有好奇心,可自行调试。这个类的作用是存储parameterObject相关的信息的,方便拿取parameterObject对应信息。
第二个要注意的就是SqlSourceBuilder类了,我们进入源码看下,先看构造方法和属性:
public class SqlSourceBuilder extends BaseBuilder {
private static final String PARAMETER_PROPERTIES = "javaType,jdbcType,mode,numericScale,resultMap,typeHandler,jdbcTypeName";
public SqlSourceBuilder(Configuration configuration) {
super(configuration);
}
public SqlSource parse(String originalSql, Class<?> parameterType, Map<String, Object> additionalParameters) {
// <1> 创建 ParameterMappingTokenHandler 对象
ParameterMappingTokenHandler handler = new ParameterMappingTokenHandler(configuration, parameterType, additionalParameters);
// <2> 创建 GenericTokenParser 对象
GenericTokenParser parser = new GenericTokenParser("#{", "}", handler);
// <3> 执行解析
String sql = parser.parse(originalSql);
// <4> 创建 StaticSqlSource 对象
return new StaticSqlSource(configuration, sql, handler.getParameterMappings());
}
}
这里又涉及到了一个内部类ParameterMappingTokenHandler:
private static class ParameterMappingTokenHandler extends BaseBuilder implements TokenHandler {
private List<ParameterMapping> parameterMappings = new ArrayList<>();
private Class<?> parameterType;
private MetaObject metaParameters;
public ParameterMappingTokenHandler(Configuration configuration, Class<?> parameterType, Map<String, Object> additionalParameters) {
super(configuration);
this.parameterType = parameterType;
this.metaParameters = configuration.newMetaObject(additionalParameters);
}
public List<ParameterMapping> getParameterMappings() {
return parameterMappings;
}
@Override
public String handleToken(String content) {
parameterMappings.add(buildParameterMapping(content));
return "?";
}
private ParameterMapping buildParameterMapping(String content) {
Map<String, String> propertiesMap = parseParameterMapping(content);
String property = propertiesMap.get("property");
Class<?> propertyType;
if (metaParameters.hasGetter(property)) { // issue #448 get type from additional params
propertyType = metaParameters.getGetterType(property);
} else if (typeHandlerRegistry.hasTypeHandler(parameterType)) {
propertyType = parameterType;
} else if (JdbcType.CURSOR.name().equals(propertiesMap.get("jdbcType"))) {
propertyType = java.sql.ResultSet.class;
} else if (property == null || Map.class.isAssignableFrom(parameterType)) {
propertyType = Object.class;
} else {
MetaClass metaClass = MetaClass.forClass(parameterType, configuration.getReflectorFactory());
if (metaClass.hasGetter(property)) {
propertyType = metaClass.getGetterType(property);
} else {
propertyType = Object.class;
}
}
ParameterMapping.Builder builder = new ParameterMapping.Builder(configuration, property, propertyType);
Class<?> javaType = propertyType;
String typeHandlerAlias = null;
for (Map.Entry<String, String> entry : propertiesMap.entrySet()) {
String name = entry.getKey();
String value = entry.getValue();
if ("javaType".equals(name)) {
javaType = resolveClass(value);
builder.javaType(javaType);
} else if ("jdbcType".equals(name)) {
builder.jdbcType(resolveJdbcType(value));
} else if ("mode".equals(name)) {
builder.mode(resolveParameterMode(value));
} else if ("numericScale".equals(name)) {
builder.numericScale(Integer.valueOf(value));
} else if ("resultMap".equals(name)) {
builder.resultMapId(value);
} else if ("typeHandler".equals(name)) {
typeHandlerAlias = value;
} else if ("jdbcTypeName".equals(name)) {
builder.jdbcTypeName(value);
} else if ("property".equals(name)) {
// Do Nothing
} else if ("expression".equals(name)) {
throw new BuilderException("Expression based parameters are not supported yet");
} else {
throw new BuilderException("An invalid property '" + name + "' was found in mapping #{" + content + "}. Valid properties are " + PARAMETER_PROPERTIES);
}
}
if (typeHandlerAlias != null) {
builder.typeHandler(resolveTypeHandler(javaType, typeHandlerAlias));
}
return builder.build();
}
private Map<String, String> parseParameterMapping(String content) {
try {
return new ParameterExpression(content);
} catch (BuilderException ex) {
throw ex;
} catch (Exception ex) {
throw new BuilderException("Parsing error was found in mapping #{" + content + "}. Check syntax #{property|(expression), var1=value1, var2=value2, ...} ", ex);
}
}
}
看了这个类是不是有点找到思路了,因为我们看到了在handleToken方法中我们返回了?,这个和我们创建动态Sql是不是有点关联了?
这里我们看到了ParameterMapping类,我们也先来看下
2. ParameterMapping源码学习
这里我们目前就只介绍它的属性和构造方法,他内置的Builder涉及到的方法太多,并且也都是取值设置值,不影响心情还是不贴了:
public class ParameterMapping {
private Configuration configuration;
private String property;
private ParameterMode mode;
private Class<?> javaType = Object.class;
private JdbcType jdbcType;
private Integer numericScale;
private TypeHandler<?> typeHandler;
private String resultMapId;
private String jdbcTypeName;
private String expression;
private ParameterMapping() {
}
}
我们再来看构造出ParameterMapping的方法buildParameterMapping:
在这个方法中我们主要讲下流程:
- 解析传进来的content内容,看是否有变量,如果有从对应参数类中获取这个属性的类型,
- 解析其存在他其他如javaType等参数设置到ParameterMapping内部的Builder方法中
- 通过Builder构建ParameterMapping
3. SqlSourceBuilder类总结
我们来总结这个类的作用。在这个类的解析方法中,我们会把整个content这样的动态语句放进去,之后通过GenericTokenParser扫描在sql中的#{}括起来的变量,把它变成?,这个流程大家应该比较熟悉,之后呢?把它封装成ParameterMapping类来记录我们取出来的,用#{}括起来的属性的相关信息,最后生成一个静态的StaticSqlSource。这样一部操作,我们整个动态Sql就已经生成完毕了。
4. 今日总结
今天我们分析了关于MyBatis解析动态sql中的#{}解析的过程,希望大家能有所收获~~~~
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