mybatis從使用到了解(五)_mybatis類型映射(TypeHandler)

mybatis的TypeHandler類型轉(zhuǎn)換

java有java的數(shù)據(jù)類型鞋诗，數(shù)據(jù)哭有數(shù)據(jù)庫的類型峭跳，當我們把java數(shù)據(jù)插入數(shù)據(jù)庫的時候，需要講java數(shù)據(jù)類型轉(zhuǎn)化為數(shù)據(jù)庫數(shù)據(jù)類型稀颁；當我們從數(shù)據(jù)庫讀取數(shù)據(jù)的時候吹菱，需要把數(shù)據(jù)庫類型轉(zhuǎn)化為java類型來處理。這中間的轉(zhuǎn)化吱韭，mybatis中是通過TypeHandler類型處理器來處理的吆豹。

我們先通過一個例子來了解TypeHandler的實現(xiàn)機制

在這個例子中講java字符數(shù)組String[]轉(zhuǎn)化成數(shù)據(jù)庫varchar類型。如：String[] interests = {"movie", "music"}轉(zhuǎn)為”movie,music"理盆，同時也能實現(xiàn)從varchar轉(zhuǎn)化為String[] 數(shù)組痘煤。

自定義類型轉(zhuǎn)化器

@MappedTypes({String[].class})
@MappedJdbcTypes({JdbcType.VARCHAR})
public class StringArrayTypeHandler extends BaseTypeHandler<String[]>{
    /**
     * 把Java類型參數(shù)轉(zhuǎn)換為對應的數(shù)據(jù)庫類型
     * @param ps 當前的PreparedStatement對象
     * @param i 當前參數(shù)位置
     * @param parameter 當前參數(shù)的Java對象
     * @param jdbcType 當前參數(shù)的數(shù)據(jù)庫類型
     * @throws SQLException
     */
    @Override
    public void setNonNullParameter(PreparedStatement ps, int i, String[] parameter, JdbcType jdbcType) throws SQLException {
        // 由于BaseTypeHandler中已經(jīng)把parameter為null的情況做了處理，所以這里我們就不用在判斷parameter是否為空猿规，直接用就可以了
        StringBuffer result = new StringBuffer();
        for (String value : parameter) {
            result.append(value).append(",");
        }
        result.deleteCharAt(result.length() - 1);
        ps.setString(i, result.toString());
    }

    /**
     * 獲取數(shù)據(jù)結果集時把數(shù)據(jù)庫類型轉(zhuǎn)換為對應的Java類型
     * @param rs 當前的結果集
     * @param columnName 當前的字段名稱
     * @return  轉(zhuǎn)換后的Java對象
     * @throws SQLException
     */
    @Override
    public String[] getNullableResult(ResultSet rs, String columnName) throws SQLException {
        return this.getStringArray(rs.getString(columnName));
    }

    /**
     * 通過字段位置獲取字段數(shù)據(jù)時把數(shù)據(jù)庫類型轉(zhuǎn)換為對應的Java類型
     * @param rs 當前的結果集
     * @param columnIndex 當前字段的位置
     * @return 轉(zhuǎn)換后的Java對象
     * @throws SQLException
     */
    @Override
    public String[] getNullableResult(ResultSet rs, int columnIndex) throws SQLException {
        return this.getStringArray(rs.getString(columnIndex));
    }

    /**
     * 調(diào)用存儲過程后把數(shù)據(jù)庫類型的數(shù)據(jù)轉(zhuǎn)換為對應的Java類型
     * @param cs  當前的CallableStatement執(zhí)行后的CallableStatement
     * @param columnIndex  當前輸出參數(shù)的位置
     * @return
     * @throws SQLException
     */
    @Override
    public String[] getNullableResult(CallableStatement cs, int columnIndex) throws SQLException {
        return this.getStringArray(cs.getString(columnIndex));
    }

    /**
     * 講”movie,music"轉(zhuǎn)化為數(shù)組對象
     * @param columnValue
     * @return
     */
    private String[] getStringArray(String columnValue) {
        if (columnValue == null)
            return null;
        return columnValue.split(",");
    }
}

配置文件里配置自定義的TypeHandler

<typeHandlers>
    <!--<typeHandler handler="com.yongssu.mybatis.demo1.StringArrayTypeHandler" javaType="[Ljava.lang.String;" jdbcType="VARCHAR"/>-->
    <typeHandler handler="com.yongssu.mybatis.demo1.StringArrayTypeHandler"/>
</typeHandlers>

如果在自定義類型轉(zhuǎn)化器時通過注解標注了對應的javaType以及jdbcType衷快，則在配置文件中不需要再次聲明；如果沒有姨俩，則需要在配置文件中說明avaType和jdbcType蘸拔。

聲明包含String[]數(shù)組的學生類

public class Student {
    private int student_id;
    private String student_name;
    private int student_age;
    private String student_phone;
    private String[] interests;
    public Student() {
        super();
    }
    public int getStudent_id() {
        return student_id;
    }
    public void setStudent_id(int student_id) {
        this.student_id = student_id;
    }
    public String getStudent_name() {
        return student_name;
    }
    public void setStudent_name(String student_name) {
        this.student_name = student_name;
    }
    public int getStudent_age() {
        return student_age;
    }
    public void setStudent_age(int student_age) {
        this.student_age = student_age;
    }
    public String getStudent_phone() {
        return student_phone;
    }
    public void setStudent_phone(String student_phone) {
        this.student_phone = student_phone;
    }
    public String[] getInterests() {
        return interests;
    }
    public void setInterests(String[] interests) {
        this.interests = interests;
    }
    @Override
    public String toString() {
        return "Student{" +
                "student_id=" + student_id +
                ", student_name='" + student_name + '\'' +
                ", student_age=" + student_age +
                ", student_phone='" + student_phone + '\'' +
                ", interests=" + Arrays.toString(interests) +
                '}';
    }
}

在stutent.xml中增加sql語句

<resultMap id="studentResult" type="Student">
    <id column="student_id" property="student_id"/>
    <result column="student_name" property="student_name"/>
    <result column="student_age" property="student_age"/>
    <result column="student_phone" property="student_phone"/>
    <result column="interests" property="interests"/>
</resultMap>

<insert id="insertStudent" parameterType="Student" useGeneratedKeys="true" keyColumn="id">
    insert into student (student_name,student_age,student_phone,interests) values
    (#{student_name},#{student_age},#{student_phone},#{interests,javaType=[Ljava.lang.String;,jdbcType=VARCHAR})
</insert>

<select id="findById" parameterType="int" resultMap="studentResult">
    select * from student where student_id = #{id}
</select>

測試類

/**
 * 方式4
 * @throws IOException
 */
public static void test04() throws IOException {
    // 讀取配置文件
    Reader reader = Resources.getResourceAsReader("config.xml");
    // 創(chuàng)建SqlSeessionFactory工廠
    SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);
    Student student = new Student();
    String[] interests = {"movie", "music"};
    student.setInterests(interests);
    student.setStudent_age(12);
    student.setStudent_name("yongsheng.su");
    student.setStudent_phone("123456");
    // 執(zhí)行sql
    SqlSession session = sqlSessionFactory.openSession();
    try {
        StudentMapper mapper = session.getMapper(StudentMapper.class);
        int result = mapper.insertStudent(student);
        System.out.println(result);
        session.commit();
    } finally {
        session.close();
    }
}

public static void test05() throws IOException {
    // 讀取配置文件
    Reader reader = Resources.getResourceAsReader("config.xml");
    // 創(chuàng)建SqlSeessionFactory工廠
    SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);

    Student student = null;
    // 執(zhí)行sql
    SqlSession session = sqlSessionFactory.openSession();
    try {
        StudentMapper mapper = session.getMapper(StudentMapper.class);
        student = mapper.selectStudent(7);
        System.out.println(student);
        session.commit();
    } finally {
        session.close();
    }
    System.out.println(student);
}

mybatis類型映射實現(xiàn)說明

通過上面的例子师郑，可以發(fā)現(xiàn)要實現(xiàn)自定義TypeHandler，只需要繼承BaseTypeHandler调窍，然后實現(xiàn)相應的轉(zhuǎn)換規(guī)則就可以宝冕。其實除了繼承BaseTypeHadler以外，還可以自己實現(xiàn)TypeHandler邓萨。通過下面代碼地梨，可以發(fā)現(xiàn)，BaseHandler也是繼承自TypeHandler先誉，并提供了一些默認的實現(xiàn)湿刽，對null值做了一些處理，這樣我們繼承BaseTypeHandler時就不需要對null值做處理了褐耳。

TypeHandler接口

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類實現(xiàn)

public abstract class BaseTypeHandler<T> extends TypeReference<T> implements TypeHandler<T> {
  protected Configuration configuration;
  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 {
    T result;
    try {
      result = getNullableResult(rs, columnName);
    } catch (Exception e) {
      throw new ResultMapException("Error attempting to get column '" + columnName + "' from result set.  Cause: " + e, e);
    }
    if (rs.wasNull()) {
      return null;
    } else {
      return result;
    }
  }
  @Override
  public T getResult(ResultSet rs, int columnIndex) throws SQLException {
    T result;
    try {
      result = getNullableResult(rs, columnIndex);
    } catch (Exception e) {
      throw new ResultMapException("Error attempting to get column #" + columnIndex+ " from result set.  Cause: " + e, e);
    }
    if (rs.wasNull()) {
      return null;
    } else {
      return result;
    }
  }
  @Override
  public T getResult(CallableStatement cs, int columnIndex) throws SQLException {
    T result;
    try {
      result = getNullableResult(cs, columnIndex);
    } catch (Exception e) {
      throw new ResultMapException("Error attempting to get column #" + columnIndex+ " from callable statement.  Cause: " + e, e);
    }
    if (cs.wasNull()) {
      return null;
    } else {
      return result;
    }
  }

  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;
}

mybatis提供的默認類型

對于一些常用的java類型，mybatis已經(jīng)提供了相應的TypeHandler,并且會自動注冊他們渴庆。mybatis提供了以下集中類型轉(zhuǎn)換器铃芦。

register(Boolean.class, new BooleanTypeHandler());
register(boolean.class, new BooleanTypeHandler());
register(JdbcType.BOOLEAN, new BooleanTypeHandler());
register(JdbcType.BIT, new BooleanTypeHandler());
register(Byte.class, new ByteTypeHandler());
register(byte.class, new ByteTypeHandler());
register(JdbcType.TINYINT, new ByteTypeHandler());
register(Short.class, new ShortTypeHandler());
register(short.class, new ShortTypeHandler());
register(JdbcType.SMALLINT, new ShortTypeHandler());
register(Integer.class, new IntegerTypeHandler());
register(int.class, new IntegerTypeHandler());
register(JdbcType.INTEGER, new IntegerTypeHandler());
register(Long.class, new LongTypeHandler());
register(long.class, new LongTypeHandler());
register(Float.class, new FloatTypeHandler());
register(float.class, new FloatTypeHandler());
register(JdbcType.FLOAT, new FloatTypeHandler());
register(Double.class, new DoubleTypeHandler());
register(double.class, new DoubleTypeHandler());
register(JdbcType.DOUBLE, new DoubleTypeHandler());
register(Reader.class, new ClobReaderTypeHandler());
register(String.class, new StringTypeHandler());
register(String.class, JdbcType.CHAR, new StringTypeHandler());
register(String.class, JdbcType.CLOB, new ClobTypeHandler());
register(String.class, JdbcType.VARCHAR, new StringTypeHandler());
register(String.class, JdbcType.LONGVARCHAR, new ClobTypeHandler());
register(String.class, JdbcType.NVARCHAR, new NStringTypeHandler());
register(String.class, JdbcType.NCHAR, new NStringTypeHandler());
register(String.class, JdbcType.NCLOB, new NClobTypeHandler());
register(JdbcType.CHAR, new StringTypeHandler());
register(JdbcType.VARCHAR, new StringTypeHandler());
register(JdbcType.CLOB, new ClobTypeHandler());
register(JdbcType.LONGVARCHAR, new ClobTypeHandler());
register(JdbcType.NVARCHAR, new NStringTypeHandler());
register(JdbcType.NCHAR, new NStringTypeHandler());
register(JdbcType.NCLOB, new NClobTypeHandler());
register(Object.class, JdbcType.ARRAY, new ArrayTypeHandler());
register(JdbcType.ARRAY, new ArrayTypeHandler());
register(BigInteger.class, new BigIntegerTypeHandler());
register(JdbcType.BIGINT, new LongTypeHandler());
register(BigDecimal.class, new BigDecimalTypeHandler());
register(JdbcType.REAL, new BigDecimalTypeHandler());
register(JdbcType.DECIMAL, new BigDecimalTypeHandler());
register(JdbcType.NUMERIC, new BigDecimalTypeHandler());
register(InputStream.class, new BlobInputStreamTypeHandler());
register(Byte[].class, new ByteObjectArrayTypeHandler());
register(Byte[].class, JdbcType.BLOB, new BlobByteObjectArrayTypeHandler());
register(Byte[].class, JdbcType.LONGVARBINARY, new BlobByteObjectArrayTypeHandler());
register(byte[].class, new ByteArrayTypeHandler());
register(byte[].class, JdbcType.BLOB, new BlobTypeHandler());
register(byte[].class, JdbcType.LONGVARBINARY, new BlobTypeHandler());
register(JdbcType.LONGVARBINARY, new BlobTypeHandler());
register(JdbcType.BLOB, new BlobTypeHandler());
register(Object.class, UNKNOWN_TYPE_HANDLER);
register(Object.class, JdbcType.OTHER, UNKNOWN_TYPE_HANDLER);
register(JdbcType.OTHER, UNKNOWN_TYPE_HANDLER);
register(Date.class, new DateTypeHandler());
register(Date.class, JdbcType.DATE, new DateOnlyTypeHandler());
register(Date.class, JdbcType.TIME, new TimeOnlyTypeHandler());
register(JdbcType.TIMESTAMP, new DateTypeHandler());
register(JdbcType.DATE, new DateOnlyTypeHandler());
register(JdbcType.TIME, new TimeOnlyTypeHandler());
register(java.sql.Date.class, new SqlDateTypeHandler());
register(java.sql.Time.class, new SqlTimeTypeHandler());
register(java.sql.Timestamp.class, new SqlTimestampTypeHandler());

參考文章：http://4443915.blog.51cto.com/4433915/1828533

最后編輯于：2017.12.05 05:16:39

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