mybatis源码解析11---ParameterHandler解析

ParameterHandler接口是参数处理器，位于mybatis包的org.apache.ibatis.executor.parameter下，源码如下：

 public interface ParameterHandler {

 Object getParameterObject();//获取参数

 void setParameters(PreparedStatement ps)//设置参数
 throws SQLException;

 }

可见ParameterHandler接口只有简单的两个方法，一个是获取参数一个是设置参数。ParameterHandler接口默认实现类是DefaultParameterHandler，主要源码如下：

 public class DefaultParameterHandler implements ParameterHandler {

 private final TypeHandlerRegistry typeHandlerRegistry;

 private final MappedStatement mappedStatement;
 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;//设置参数
 this.boundSql = boundSql;
 }

 @Override
 public Object getParameterObject() {
 return parameterObject;//返回参数
 }

 @Override
 public void setParameters(PreparedStatement ps) {
 ErrorContext.instance().activity("setting parameters").object(mappedStatement.getParameterMap().getId());
 List<ParameterMapping> parameterMappings = boundSql.getParameterMappings();//获取所有参数，ParameterMapping是jdbc和java类型之间的对应关系
 if (parameterMappings != null) {
 //遍历所有参数，将java 类型设置成jdbc类型
 for (int i = 0; i < parameterMappings.size(); i++) {
 ParameterMapping parameterMapping = parameterMappings.get(i);
 if (parameterMapping.getMode() != ParameterMode.OUT) {
 Object value;
 String propertyName = parameterMapping.getProperty();
 if (boundSql.hasAdditionalParameter(propertyName)) { // issue #448 ask first for additional params
 value = boundSql.getAdditionalParameter(propertyName);
 } else if (parameterObject == null) {
 value = null;
 } else if (typeHandlerRegistry.hasTypeHandler(parameterObject.getClass())) {
 value = parameterObject;
 } else {
 MetaObject metaObject = configuration.newMetaObject(parameterObject);
 value = metaObject.getValue(propertyName);
 }
 TypeHandler typeHandler = parameterMapping.getTypeHandler();
 JdbcType jdbcType = parameterMapping.getJdbcType();
 if (value == null && jdbcType == null) {
 jdbcType = configuration.getJdbcTypeForNull();
 }
 try {
 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);
 }
 }
 }
 }
 }

 }

而ParameterHandler的初始化同样也是在Configuration中实现的，代码如下：

   public ParameterHandler newParameterHandler(MappedStatement mappedStatement, Object parameterObject, BoundSql boundSql) {
     ParameterHandler parameterHandler = mappedStatement.getLang().createParameterHandler(mappedStatement, parameterObject, boundSql);
     parameterHandler = (ParameterHandler) interceptorChain.pluginAll(parameterHandler);
     return parameterHandler;
   }