前言

TypeHandler

TypeHandler 是 Mybatis 中的类型处理器，用于 JavaType 和 JdbcType 之间的切换

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public interface TypeHandler<T> {

  void setParameter(PreparedStatement ps, int i, T parameter, JdbcType jdbcType) throws SQLException;

  T getResult(ResultSet rs, String columnName) throws SQLException;

  T getResult(ResultSet rs, int columnIndex) throws SQLException;

  T getResult(CallableStatement cs, int columnIndex) throws SQLException;

}

BaseTypeHandler

BaseTypeHandler 是在 TypeHandler 的基础上做的一层封装，让类型处理器的实现更加简单

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public abstract class BaseTypeHandler<T> extends TypeReference<T> implements TypeHandler<T> {

  @Deprecated
  protected Configuration configuration;

  @Deprecated
  public void setConfiguration(Configuration c) {
    this.configuration = c;
  }

  @Override
  public void setParameter(PreparedStatement ps, int i, T parameter, JdbcType jdbcType) throws SQLException {
    if (parameter == null) {
      if (jdbcType == null) {
        throw new TypeException("JDBC requires that the JdbcType must be specified for all nullable parameters.");
      }
      try {
        ps.setNull(i, jdbcType.TYPE_CODE);
      } catch (SQLException e) {
        throw new TypeException("Error setting null for parameter #" + i + " with JdbcType " + jdbcType + " . "
              + "Try setting a different JdbcType for this parameter or a different jdbcTypeForNull configuration property. "
              + "Cause: " + e, e);
      }
    } else {
      try {
        setNonNullParameter(ps, i, parameter, jdbcType);
      } catch (Exception e) {
        throw new TypeException("Error setting non null for parameter #" + i + " with JdbcType " + jdbcType + " . "
              + "Try setting a different JdbcType for this parameter or a different configuration property. "
              + "Cause: " + e, e);
      }
    }
  }

  @Override
  public T getResult(ResultSet rs, String columnName) throws SQLException {
    try {
      return getNullableResult(rs, columnName);
    } catch (Exception e) {
      throw new ResultMapException("Error attempting to get column '" + columnName + "' from result set.  Cause: " + e, e);
    }
  }

  @Override
  public T getResult(ResultSet rs, int columnIndex) throws SQLException {
    try {
      return getNullableResult(rs, columnIndex);
    } catch (Exception e) {
      throw new ResultMapException("Error attempting to get column #" + columnIndex + " from result set.  Cause: " + e, e);
    }
  }

  @Override
  public T getResult(CallableStatement cs, int columnIndex) throws SQLException {
    try {
      return getNullableResult(cs, columnIndex);
    } catch (Exception e) {
      throw new ResultMapException("Error attempting to get column #" + columnIndex + " from callable statement.  Cause: " + e, e);
    }
  }

  public abstract void setNonNullParameter(PreparedStatement ps, int i, T parameter, JdbcType jdbcType) throws SQLException;

  public abstract T getNullableResult(ResultSet rs, String columnName) throws SQLException;

  public abstract T getNullableResult(ResultSet rs, int columnIndex) throws SQLException;

  public abstract T getNullableResult(CallableStatement cs, int columnIndex) throws SQLException;

}

SpringBoot 实现自定义TypeHandler

以下是自定义的类型处理器，作用是将 String[] 转换为 varchar 

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@MappedTypes(String[].class)
@MappedJdbcTypes(JdbcType.VARCHAR)
public class StringArrayHandlerType extends BaseTypeHandler<String[]> {


    @Override
    public void setNonNullParameter(PreparedStatement preparedStatement, int i, String[] strings, JdbcType jdbcType) throws SQLException {
        preparedStatement.setString(i, StringUtils.join(Arrays.asList(strings), ","));
    }

    @Override
    public String[] getNullableResult(ResultSet resultSet, String s) throws SQLException {
        return this.getStringArray(resultSet.getString(s));
    }

    @Override
    public String[] getNullableResult(ResultSet resultSet, int i) throws SQLException {
        return this.getStringArray(resultSet.getString(i));
    }

    @Override
    public String[] getNullableResult(CallableStatement callableStatement, int i) throws SQLException {
        return this.getStringArray(callableStatement.getString(i));
    }

    private String[] getStringArray(String s){
        return s.split(",");
    }
}

application.yml

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mybatis:
  mapperLocations: classpath:mapper/*.xml
  type-handlers-package: com.yxd.sharding.mybatis

测试

User.java

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@Data
public class User {
    private String username;
    private String password;
    private String[] hobbies;
}

UserMapper.java

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@Mapper
public interface UserMapper {
    @Insert("INSERT INTO user (`username`, `password`, `hobbies`) VALUES(#{username}, #{password}, #{hobbies})")
    int insert(User user);

    @Select("SELECT * FROM user WHERE id = #{id}")
    User getById(Integer id);
}

数据库：user

字段名 类型
id int
username varchar
password varchar
hobbies varchar

单元测试：

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@Test
void insert() {
    User user = new User();
    user.setUsername("yuxudong");
    user.setPassword("123456");
    String[] hobbies = {"唱", "跳", "rap", "篮球"};
    user.setHobbies(hobbies);
    // 插入成功
    userMapper.insert(user);
}

@Test
void get() {
    User user = userMapper.getById(1);
    // User(username=yuxudong, password=123456, hobbies=[唱, 跳, rap, 篮球])
    System.out.println(user);
}

数据库中的结果

id username password hobbies
1 yuxudong 123456 唱, 跳, rap, 篮球