Mybatis源码分析之参数映射及处理ParameterHandler

ParameterHandler是用来设置参数规则的，当StatementHandler调用prepare方法之后，接下来就是调用它来进行设置参数。

ParameterHandler接口：

public interface ParameterHandler {

Object getParameterObject();

void setParameters(PreparedStatement ps)
throws SQLException;

}

getParameterObject是用来获取参数的，setParameters(PreparedStatement ps)是用来设置参数的，相当于对sql中所有的参数都执行ps.setXXX(value);

ParameterHandler的默认实现类是DefaultParameterHandler，其实现了接口中定义的两个方法。

getParameterObject是获取参数，这个参数值就是你传递进来的值，可能是个实体、map或单个基本类型数据。

@Override
public Object getParameterObject() {
return parameterObject;
}

设置参数，其实就是你在sql语句中配置的java对象和jdbc类型对应的关系#{id,jdbcType=INTEGER}，id默认类型是javaType=class java.lang.Integer。

//设置参数
@Override
public void setParameters(PreparedStatement ps) {
ErrorContext.instance().activity("setting parameters").object(mappedStatement.getParameterMap().getId());
//获取所有参数，ParameterMapping是java类型和jdbc类型的对应关系
List<ParameterMapping> parameterMappings = boundSql.getParameterMappings();
if (parameterMappings != null) {
for (int i = 0; i < parameterMappings.size(); i++) {
ParameterMapping parameterMapping = parameterMappings.get(i);
if (parameterMapping.getMode() != ParameterMode.OUT) {
//参数值
Object value;
//获取参数名称
String propertyName = parameterMapping.getProperty();
if (boundSql.hasAdditionalParameter(propertyName)) { // issue #448 ask first for additional params
//获取参数值
value = boundSql.getAdditionalParameter(propertyName);
} else if (parameterObject == null) {
value = null;
} else if (typeHandlerRegistry.hasTypeHandler(parameterObject.getClass())) {
//如果是单个值则直接赋值
value = parameterObject;
} else {
MetaObject metaObject = configuration.newMetaObject(parameterObject);
value = metaObject.getValue(propertyName);
}
//获取参数值对应的jdbc类型
TypeHandler typeHandler = parameterMapping.getTypeHandler();
JdbcType jdbcType = parameterMapping.getJdbcType();
if (value == null && jdbcType == null) {
jdbcType = configuration.getJdbcTypeForNull();
}
try {
//设置参数值和jdbc类型的对应关系
typeHandler.setParameter(ps, i + 1, value, jdbcType);
} catch (TypeException e) {
throw new TypeException("Could not set parameters for mapping: " + parameterMapping + ". Cause: " + e, e);
} catch (SQLException e) {
throw new TypeException("Could not set parameters for mapping: " + parameterMapping + ". Cause: " + e, e);
}
}
}
}
}

这样就设置了一个参数值对应的jdbcType了

完整的DefaultParameterHandler源码如下：

/**
* @author Clinton Begin
* @author Eduardo Macarron
*/
public class DefaultParameterHandler implements ParameterHandler {

private final TypeHandlerRegistry typeHandlerRegistry;

private final MappedStatement mappedStatement;
//所有的参数值
private final Object parameterObject;
private BoundSql boundSql;
private Configuration configuration;

public DefaultParameterHandler(MappedStatement mappedStatement, Object parameterObject, BoundSql boundSql) {
this.mappedStatement = mappedStatement;
this.configuration = mappedStatement.getConfiguration();
this.typeHandlerRegistry = mappedStatement.getConfiguration().getTypeHandlerRegistry();
this.parameterObject = parameterObject;
this.boundSql = boundSql;
}

@Override
public Object getParameterObject() {
return parameterObject;
}
//设置参数
@Override
public void setParameters(PreparedStatement ps) {
ErrorContext.instance().activity("setting parameters").object(mappedStatement.getParameterMap().getId());
//获取所有参数，ParameterMapping是java类型和jdbc类型的对应关系
List<ParameterMapping> parameterMappings = boundSql.getParameterMappings();
if (parameterMappings != null) {
for (int i = 0; i < parameterMappings.size(); i++) {
ParameterMapping parameterMapping = parameterMappings.get(i);
if (parameterMapping.getMode() != ParameterMode.OUT) {
//参数值
Object value;
//获取参数名称
String propertyName = parameterMapping.getProperty();
if (boundSql.hasAdditionalParameter(propertyName)) { // issue #448 ask first for additional params
//获取参数值
value = boundSql.getAdditionalParameter(propertyName);
} else if (parameterObject == null) {
value = null;
} else if (typeHandlerRegistry.hasTypeHandler(parameterObject.getClass())) {
//如果是单个值则直接赋值
value = parameterObject;
} else {
MetaObject metaObject = configuration.newMetaObject(parameterObject);
value = metaObject.getValue(propertyName);
}
//获取参数值对应的jdbc类型
TypeHandler typeHandler = parameterMapping.getTypeHandler();
JdbcType jdbcType = parameterMapping.getJdbcType();
if (value == null && jdbcType == null) {
jdbcType = configuration.getJdbcTypeForNull();
}
try {
//设置参数值和jdbc类型的对应关系
typeHandler.setParameter(ps, i + 1, value, jdbcType);
} catch (TypeException e) {
throw new TypeException("Could not set parameters for mapping: " + parameterMapping + ". Cause: " + e, e);
} catch (SQLException e) {
throw new TypeException("Could not set parameters for mapping: " + parameterMapping + ". Cause: " + e, e);
}
}
}
}
}

}