Mybatis源码分析之参数映射及处理ParameterHandler

太过爱你忘了你带给我的痛 2022-07-15 12:53 310阅读 0赞

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);
              }
            }
          }
        }
      }
    
    }