MyBatis获取自增长主键值的两种方式及源码浅析

CREATE TABLE `user` (
	`id` INT(11) NOT NULL AUTO_INCREMENT,
	`user_name` VARCHAR(32) NULL DEFAULT NULL,
	`pass_word` VARCHAR(16) NULL DEFAULT NULL,
	`address` VARCHAR(16) NULL DEFAULT NULL,
	PRIMARY KEY (`id`)
)
COLLATE='utf8_general_ci'
ENGINE=InnoDB
;

public class UserScope implements Serializable{

    /**
     * 姓名
     */
    private String userName;
    /**
     * 主键ID
     */
    private Integer id;
    /**
     * 密码
     */
    private String passWord;
    /**
     * 地址
     */
    private String address;
}

    @Override
    public void addUser(UserScope userScope) {
        this.getSqlSession().insert("userMapper.addUser",userScope);
    }

    @Override
    public int addUserSelectKey(UserScope userScope){

        this.getSqlSession().insert("userMapper.insertSelectKey",userScope);
        System.out.println(userScope);
        return userScope.getId();//获取自增长主键值
    }

Mapper.xml

<mapper namespace="userMapper">
    <insert id="addUser" parameterType="userScope" useGeneratedKeys="true" keyProperty="id">
        insert user(user_name,pass_word,address) values (#{userName},#{passWord},#{address})
    </insert>
    <insert id="insertSelectKey" parameterType="userScope">
        <selectKey keyProperty="id" resultType="int">
            select LAST_INSERT_ID()
        </selectKey>
        insert user(user_name,pass_word,address) values (#{userName},#{passWord},#{address})
    </insert>
</mapper>

  @Override
  public int update(String statement, Object parameter) {
    try {
      dirty = true;
      //这里是根据命名空间和ID获取要执行的sql的信息	
      MappedStatement ms = configuration.getMappedStatement(statement);
      return executor.update(ms, wrapCollection(parameter));//执行sql
    } catch (Exception e) {
      throw ExceptionFactory.wrapException("Error updating database.  Cause: " + e, e);
    } finally {
      ErrorContext.instance().reset();
    }
  }

BaseExecutor

  @Override
  public int update(MappedStatement ms, Object parameter) throws SQLException {
    ErrorContext.instance().resource(ms.getResource()).activity("executing an update").object(ms.getId());//记录操作信息，如果有异常的话，会从这里取异常信息
    if (closed) {
      throw new ExecutorException("Executor was closed.");
    }
    clearLocalCache();//清空本地缓存
    return doUpdate(ms, parameter);//执行sql
  }

SimpleExecutor

  public int doUpdate(MappedStatement ms, Object parameter) throws SQLException {
    Statement stmt = null;
    try {
      Configuration configuration = ms.getConfiguration();
      StatementHandler handler = configuration.newStatementHandler(this, ms, parameter, RowBounds.DEFAULT, null, null);//获取执行sql的Statement
      stmt = prepareStatement(handler, ms.getStatementLog());//封装StatementHandler的信息。打开连接、事务是否超时等。
      return handler.update(stmt);//执行sql
    } finally {
      closeStatement(stmt);
    }
  }

PreparedStatementHandler

  public int update(Statement statement) throws SQLException {
    PreparedStatement ps = (PreparedStatement) statement;
    ps.execute();//这里是调用的JDBC4PreparedStatement执行sql
    int rows = ps.getUpdateCount();//获取受影响的行数，也就是调用插入操作的时候返回的真正值。
    Object parameterObject = boundSql.getParameterObject();//获取参数对象
    KeyGenerator keyGenerator = mappedStatement.getKeyGenerator();//判断是那种KeyGenerator
    keyGenerator.processAfter(executor, mappedStatement, ps, parameterObject);//根据KeyGenerator去set主键值
    return rows;
  }

StatementHandler的UML图如下

KeyGenerator

  public void processBatch(MappedStatement ms, Statement stmt, Collection<Object> parameters) {
    ResultSet rs = null;
    try {
      rs = stmt.getGeneratedKeys();//获取执行结果值
      final Configuration configuration = ms.getConfiguration();
      final TypeHandlerRegistry typeHandlerRegistry = configuration.getTypeHandlerRegistry();
      final String[] keyProperties = ms.getKeyProperties();//获取设置的keyProperty
      final ResultSetMetaData rsmd = rs.getMetaData();
      TypeHandler<?>[] typeHandlers = null;
      if (keyProperties != null && rsmd.getColumnCount() >= keyProperties.length) {//如果设置了keyProperty，则在参数对象中放入处理之后的结果值
        for (Object parameter : parameters) {
          // there should be one row for each statement (also one for each parameter)
          if (!rs.next()) {
            break;
          }
          final MetaObject metaParam = configuration.newMetaObject(parameter);
          if (typeHandlers == null) {
            typeHandlers = getTypeHandlers(typeHandlerRegistry, metaParam, keyProperties, rsmd);//keyProperty设置的字段类型的处理器
          }
          populateKeys(rs, metaParam, keyProperties, typeHandlers);//在参数对象中设置keyProperty的字段值
        }
      }

  private void populateKeys(ResultSet rs, MetaObject metaParam, String[] keyProperties, TypeHandler<?>[] typeHandlers) throws SQLException {
    for (int i = 0; i < keyProperties.length; i++) {
      TypeHandler<?> th = typeHandlers[i];
      if (th != null) {
        Object value = th.getResult(rs, i + 1);
        metaParam.setValue(keyProperties[i], value);//在参数对象中设置keyProperty的字段值
      }
    }
  }

  public void setValue(String name, Object value) {
    PropertyTokenizer prop = new PropertyTokenizer(name);
    if (prop.hasNext()) {
      MetaObject metaValue = metaObjectForProperty(prop.getIndexedName());
      if (metaValue == SystemMetaObject.NULL_META_OBJECT) {
        if (value == null && prop.getChildren() != null) {
          // don't instantiate child path if value is null
          return;
        } else {
          metaValue = objectWrapper.instantiatePropertyValue(name, prop, objectFactory);
        }
      }
      metaValue.setValue(prop.getChildren(), value);
    } else {
      objectWrapper.set(prop, value);//在参数对象中设置keyProperty的字段值（根据反射来操作的）
    }
  }

  private void setBeanProperty(PropertyTokenizer prop, Object object, Object value) {
    try {
      Invoker method = metaClass.getSetInvoker(prop.getName());
      Object[] params = {value};
      try {
        method.invoke(object, params);//设置参数对象的值
      }

对象组装器的类图如下：主要有对象组装器、集合组装器、Map组装器

  public Object invoke(Object target, Object[] args) throws IllegalAccessException, InvocationTargetException {
    field.set(target, args[0]);//这个field对象就是java.lang.reflect.Field对象。
    return null;
  }

    public void addUserBatch(List<UserScope> list) {

        this.getSqlSession().insert("userMapper.addUserBatch",list);
        System.out.println(Arrays.toString(list.toArray()));
    }

    <insert id="addUserBatch" parameterType="java.util.List" useGeneratedKeys="true" keyProperty="id" keyColumn="id">
      insert user(user_name,pass_word,address) values
      <foreach collection="list" item="item" separator=",">
          ( #{item.userName},#{item.passWord},#{item.address} )
      </foreach>
    </insert>