Mybatis 使用自定义泛型 typehandler 并且 bean 属性名称和表的列相同时，选择会引发 ClassCastException

Question

我是 Mybatis 的新手。最近在使用自定义泛型typeHander，当bean属性与表的列名相同时，select会引发ClassCastException。

以下是配置

mybatis-configuration.xml

<typeHandlers>
        <typeHandler handler="com.sut.util.enumerate.mybatis.GenericEnumUserType"
            javaType="com.sut.util.meta.WhetherTypeEnum" jdbcType="CHAR"/>
        <typeHandler handler="com.sut.util.enumerate.mybatis.GenericEnumUserType"
            javaType="com.sut.util.meta.SexTypeEnum" jdbcType="CHAR" />
        <typeHandler handler="com.sut.util.enumerate.mybatis.GenericEnumUserType"
            javaType="com.sut.util.meta.ArticleTypeEnum" jdbcType="CHAR" />
        <typeHandler handler="com.sut.util.enumerate.mybatis.GenericEnumUserType"
            javaType="com.sut.util.meta.EducationLevelEnum" jdbcType="CHAR" />
        <typeHandler handler="com.sut.util.enumerate.mybatis.GenericEnumUserType"
            javaType="com.sut.util.meta.ServiceLevelEnum" jdbcType="CHAR" />
        <typeHandler handler="com.sut.util.enumerate.mybatis.GenericEnumUserType"
            javaType="com.sut.util.meta.ServiceTypeEnum" jdbcType="CHAR" />
        <typeHandler handler="com.sut.util.enumerate.mybatis.GenericEnumUserType"
            javaType="com.sut.util.meta.StaffLevelEnum" jdbcType="CHAR" />
        <typeHandler handler="com.sut.util.enumerate.mybatis.GenericEnumUserType"
            javaType="com.sut.util.meta.ArticleStatusEnum" jdbcType="CHAR" />
        <typeHandler handler="com.sut.util.enumerate.mybatis.GenericEnumUserType"
            javaType="com.sut.util.meta.HealthyStatusEnum" jdbcType="CHAR" />
</typeHandlers>

staffMapper.xml

 <resultMap type="com.sut.persist.entity.Staff" id="staff">
    <id property="id" javaType="int" column="id" />
    <result property="staffName" javaType="String" column="STAFF_NAME" />
    <result property="imgPath" javaType="String" column="IMG_PATH" />
    <result property="staffLevel" javaType="com.sut.util.meta.StaffLevelEnum" column="LEVEL"
        typeHandler="com.sut.util.enumerate.mybatis.GenericEnumUserType" jdbcType="CHAR"/>
    <result property="birthDate" javaType="java.util.Date" column="BIRTH_DATE" />
    <result property="address" javaType="String" column="address" />
    <result property="healthyStatus" javaType="com.sut.util.meta.HealthyStatusEnum" column="HEALTHY_STATUS"
        typeHandler="com.sut.util.enumerate.mybatis.GenericEnumUserType" jdbcType="CHAR" />
    <result property="education" column="education" typeHandler="com.sut.util.enumerate.mybatis.GenericEnumUserType" /> 
    <result property="workYears" javaType="integer" column="WORK_YEARS" />
    <result property="selfIntroduction" javaType="String" column="SELF_INTRODUCTION" />
    <result property="cert" javaType="String" column="CERT" />
    <result property="remark" javaType="String" column="REMARK" />
    <result property="serviceType" javaType="com.sut.util.meta.ServiceTypeEnum" column="SERVICE_TYPE"
        typeHandler="com.sut.util.enumerate.mybatis.GenericEnumUserType" /> 
    <result property="mobile" javaType="String" column="MOBILE" />
    <result property="qqNumber" javaType="String" column="QQ_NUMBER" />
    <result property="webchatNumber" javaType="String" column="WEBCHAT_NUMBER" />
    <result property="webchatQrcode" javaType="String" column="WEBCHAT_QRCODE" />   
</resultMap>

<!-- query user by id -->
<select id="getById" parameterType="long"  resultMap="staff">
    select
        staff_id,
        staff_name,
        img_path,
        level as staffLevel,
        birth_date,
        address,
        healthy_status as healthyStatus,
        education as education, 
        work_years,
        self_introduction,
        cert,
        remark,
        service_type as serviceType,
        mobile,
        qq_number,
        webchat_number,
        webchat_qrcode
    from bbs_staff where staff_id = #{id}

Staff.java：

public class Staff implements java.io.Serializable {

    private static final long serialVersionUID = 1L;

    private long id;
    private String staffName;
    private String imgPath;
    private StaffLevelEnum staffLevel;
    private java.util.Date birthDate;
    private java.lang.String address;
    private HealthyStatusEnum healthyStatus;
    private EducationLevelEnum educationLevel;
    private int workYears;
    private String selfIntroduction;
    private String cert;
    private String remark;
    private ServiceTypeEnum serviceType;
    private String mobile;
    private String qqNumber;
    private String webchatNumber;
    private String webchatQrcode;

    /**
     * default Constructor
     */
    public Staff() {
        super();
    }


    public long getId() {
        return id;
    }


    public void setId(long id) {
        this.id = id;
    }


    public String getStaffName() {
        return staffName;
    }

    public void setStaffName(String staffName) {
        this.staffName = staffName;
    }

    public String getImgPath() {
        return imgPath;
    }

    public void setImgPath(String imgPath) {
        this.imgPath = imgPath;
    }


    public StaffLevelEnum getStaffLevel() {
        return staffLevel;
    }


    public void setStaffLevel(StaffLevelEnum staffLevel) {
        this.staffLevel = staffLevel;
    }


    public java.util.Date getBirthDate() {
        return birthDate;
    }

    public void setBirthDate(java.util.Date birthDate) {
        this.birthDate = birthDate;
    }

    public java.lang.String getAddress() {
        return address;
    }

    public void setAddress(java.lang.String address) {
        this.address = address;
    }

    public HealthyStatusEnum getHealthyStatus() {
        return healthyStatus;
    }

    public void setHealthyStatus(HealthyStatusEnum healthyStatus) {
        this.healthyStatus = healthyStatus;
    }

    public EducationLevelEnum getEducationLevel() {
        return educationLevel;
    }


    public void setEducationLevel(EducationLevelEnum educationLevel) {
        this.educationLevel = educationLevel;
    }

    public int getWorkYears() {
        return workYears;
    }

    public void setWorkYears(int workYears) {
        this.workYears = workYears;
    }


    public String getSelfIntroduction() {
        return selfIntroduction;
    }


    public void setSelfIntroduction(String selfIntroduction) {
        this.selfIntroduction = selfIntroduction;
    }

    public String getCert() {
        return cert;
    }

    public void setCert(String cert) {
        this.cert = cert;
    }

    public String getRemark() {
        return remark;
    }

    public void setRemark(String remark) {
        this.remark = remark;
    }

    public ServiceTypeEnum getServiceType() {
        return serviceType;
    }

    public void setServiceType(ServiceTypeEnum serviceType) {
        this.serviceType = serviceType;
    }

    public String getMobile() {
        return mobile;
    }

    public void setMobile(String mobile) {
        this.mobile = mobile;
    }

    public String getQqNumber() {
        return qqNumber;
    }

    public void setQqNumber(String qqNumber) {
        this.qqNumber = qqNumber;
    }

    public String getWebchatNumber() {
        return webchatNumber;
    }

    public void setWebchatNumber(String webchatNumber) {
        this.webchatNumber = webchatNumber;
    }

    public String getWebchatQrcode() {
        return webchatQrcode;
    }

    public void setWebchatQrcode(String webchatQrcode) {
        this.webchatQrcode = webchatQrcode;
    }

    @Override
    public String toString() {
        return MoreObjects.toStringHelper(Staff.class)
                .add("id", id)
                .add("staffName", staffName)
                .add("imgPath", imgPath)
                .add("level", staffLevel)
                .add("birthDate", birthDate)
                .add("address", address)
                .add("healthyStatus", healthyStatus)
                .add("education", educationLevel)
                .add("workYears", workYears)
                .add("selfIntroduction", selfIntroduction)
                .add("cert", cert)
                .add("remark", remark)
                .add("serviceType", serviceType)
                .add("mobile", mobile)
                .add("qqNumber", qqNumber)
                .add("webChatNumber", webchatNumber)
                .add("webChatQrcode", webchatQrcode)
                .toString();
    }

}

com.sut.util.enumerate.mybatis.GenericEnumUserType：

public class GenericEnumUserType<E extends StringEnumTypeImp> extends BaseTypeHandler<E>{

    private static final Logger LOG = LoggerFactory.getLogger(GenericEnumUserType.class);

    //mybatis will pass actual class when constructing TypeHandler
    private Class<E> type;

    private static final String fromStringCode = "fromStringCode";

    public GenericEnumUserType(Class<E> type){
        Preconditions.checkNotNull(type, "Type argument cannot be null");
        this.type = type;
    }

    /**
     * @see org.apache.ibatis.type.BaseTypeHandler#setNonNullParameter(java.sql.PreparedStatement, int, java.lang.Object, org.apache.ibatis.type.JdbcType)
     */
    @Override
    public void setNonNullParameter(PreparedStatement ps, int i, StringEnumTypeImp parameter, JdbcType jdbcType) throws SQLException {
        ps.setString(i, parameter.getStoreValue());
    }

    /**
     * getResult and use reflect 
     * @see org.apache.ibatis.type.BaseTypeHandler#getNullableResult(java.sql.ResultSet, java.lang.String)
     */
    @Override
    @SuppressWarnings("unchecked")
    public E getNullableResult(ResultSet rs, String columnName) throws SQLException {
        LOG.info("return type is : {}", type);
        String storeValue =  rs.getString(columnName);
        Preconditions.checkNotNull(type, "Type argument cannot be null");
        try {
            Method fromMethod = type.getMethod(fromStringCode, String.class);
            return (E) fromMethod.invoke(null, storeValue);
        } catch (IllegalAccessException | NoSuchMethodException | SecurityException | IllegalArgumentException | InvocationTargetException e) {
            e.printStackTrace();
        }
        return null;
    }

    /**
     * 
     * @see org.apache.ibatis.type.BaseTypeHandler#getNullableResult(java.sql.ResultSet, int)
     */
    @SuppressWarnings("unchecked")
    @Override
    public E getNullableResult(ResultSet rs, int columnIndex) throws SQLException {
        LOG.info("return type is {}", type);
        String storeValue =  rs.getString(columnIndex);
        Preconditions.checkNotNull(type, "Type argument cannot be null");
        try {
            Method fromMethod = type.getMethod(fromStringCode, String.class);
            return (E) fromMethod.invoke(null, storeValue);
        } catch (IllegalAccessException | NoSuchMethodException | SecurityException | IllegalArgumentException | InvocationTargetException e) {
            e.printStackTrace();
        }
        return null;
    }

    /**
     * not used
     * @see org.apache.ibatis.type.BaseTypeHandler#getNullableResult(java.sql.CallableStatement, int)
     */
    @Override
    public E getNullableResult(CallableStatement cs, int columnIndex) throws SQLException {
        try {
            return type.newInstance();
        } catch (InstantiationException | IllegalAccessException e) {
            e.printStackTrace();
        }
        return null;
    }

}

调用getById方法时，会抛出异常：

Struts has detected an unhandled exception:

Messages:   
java.lang.ClassCastException@6f26a5f5
Could not set property 'education' of 'class com.sut.persist.entity.Staff' with value 'com.sut.util.meta.HealthyStatusEnum@3b554a50' Cause: java.lang.IllegalArgumentException: java.lang.ClassCastException@6f26a5f5
nested exception is org.apache.ibatis.reflection.ReflectionException: Could not set property 'education' of 'class com.sut.persist.entity.Staff' with value 'com.sut.util.meta.HealthyStatusEnum@3b554a50' Cause: java.lang.IllegalArgumentException: java.lang.ClassCastException@6f26a5f5 

mybatis 文档说在使用 Generic TypeHandler 时，它会得到 By JavaType，即使 jdbcType 为 null，它也会得到正确的 TypeHandler。我检查了三遍配置，并调试了源代码。然后我发现 ResultSetWrapper 会将列分离为 mappedColumns 和 UnmappedColumns，unmappedColumns 将返回正确的 TypeHandler，而 mappedColumns 不会。我很好奇为什么会这样。这是一个错误还是我的配置不正确。

环境：
Mybatis : 3.4.1
MySQL : 5.6

任何帮助将不胜感激！

Answer 1

在您的实际mapper.xml 中，您可以尝试对枚举处理类型执行以下操作

<result property="educationLevel" column="education" javaType="com.sut.util.meta.EducationLevelEnum" jdbcType="CHAR" />

• 匹配属性name 来自您的 POJO 教育级别而不是教育
• 提供javaType和jdbcType
• 从结果映射中移除handler（让mybatis去做）