大龄菜鸟-》 mybatis 源码阅读-》 exceptions 异常模块

马上快过年了，今年的年过的很不一样，新冠也不知道啥时候可以彻底消灭。

财务不自由的我。决定留在大上海，过年如果没事干就写写文章。欧耶~

活着就去做想做的事！不推迟不放弃。

进入主题

一：目录总览

异常模块的东西看着是不多哈。相比之前的反射模块，这个看起来真的比较轻松。

实际上，mybatis的异常类并非全部定义在这个目录下。其他的包下也是有的。下面整理罗列了下

这些异常类代码都是相同的。所以，这里就简单整理如下：

reflection 包：ReflectionException
logging 包：LogException
builder 包：BuilderException、IncompleteElementException
scripting 包：ScriptingException
binding 包：BindingException
type 包：TypeException
session 包：SqlSessionException
cache 包：CacheException
transaction 包：TransactionException
datasource 包：DataSourceException
executor 包：ResultMapException、ExecutorException、BatchExecutorException
plugin 包：PluginException

二： IbatisException 类继承 RuntimeException,IBatis 的异常基类，具体代码如下。

package org.apache.ibatis.exceptions;

/**
 * @author Clinton Begin
 */
@Deprecated
public class IbatisException extends RuntimeException {

  private static final long serialVersionUID = 3880206998166270511L;

  public IbatisException() {
    super();
  }

  public IbatisException(String message) {
    super(message);
  }

  public IbatisException(String message, Throwable cause) {
    super(message, cause);
  }

  public IbatisException(Throwable cause) {
    super(cause);
  }

}

三： PersistenceException，继承 IbatisException 类，目前 MyBatis 真正的异常基类。代码如下：

package org.apache.ibatis.exceptions;

/**
 * @author Clinton Begin
 */
@SuppressWarnings("deprecation")
public class PersistenceException extends IbatisException {

  private static final long serialVersionUID = -7537395265357977271L;

  public PersistenceException() {
    super();
  }

  public PersistenceException(String message) {
    super(message);
  }

  public PersistenceException(String message, Throwable cause) {
    super(message, cause);
  }

  public PersistenceException(Throwable cause) {
    super(cause);
  }
}

四：TooManyResultsException，继承 PersistenceException 类，查询返回过多结果的异常。期望返回一条，实际返回了多条。代码如下：

/**
 *    Copyright 2009-2015 the original author or authors.
 *
 *    Licensed under the Apache License, Version 2.0 (the "License");
 *    you may not use this file except in compliance with the License.
 *    You may obtain a copy of the License at
 *
 *       http://www.apache.org/licenses/LICENSE-2.0
 *
 *    Unless required by applicable law or agreed to in writing, software
 *    distributed under the License is distributed on an "AS IS" BASIS,
 *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *    See the License for the specific language governing permissions and
 *    limitations under the License.
 */
package org.apache.ibatis.exceptions;

/**
 * 继承 PersistenceException 类，查询返回过多结果的异常
 * 期望返回一条，实际返回了多条。代码如下：
 * @author Clinton Begin
 */
public class TooManyResultsException extends PersistenceException {

  private static final long serialVersionUID = 8935197089745865786L;

  public TooManyResultsException() {
    super();
  }

  public TooManyResultsException(String message) {
    super(message);
  }

  public TooManyResultsException(String message, Throwable cause) {
    super(message, cause);
  }

  public TooManyResultsException(Throwable cause) {
    super(cause);
  }
}

五： ExceptionFactory ,就是进行下异常的包装

package org.apache.ibatis.exceptions;

import org.apache.ibatis.executor.ErrorContext;

/**
 * @author Clinton Begin
 */
public class ExceptionFactory {

  private ExceptionFactory() {
    // Prevent Instantiation
  }
  /**
   * 包装异常成 PersistenceException
   *
   * @param message 消息
   * @param e 发生的异常
   * @return PersistenceException
   */
  public static RuntimeException wrapException(String message, Exception e) {
    // 因为instance 和 message 和 cause 这些方法都是单独调用的，
    // 所以 instance用了本地线程变量。来保存线程上下的值。
    return new PersistenceException(ErrorContext.instance().message(message).cause(e).toString(), e);
  }

}


/**
 *  ErrorContext  对象
 *    Copyright 2009-2020 the original author or authors.
 *
 *    Licensed under the Apache License, Version 2.0 (the "License");
 *    you may not use this file except in compliance with the License.
 *    You may obtain a copy of the License at
 *
 *       http://www.apache.org/licenses/LICENSE-2.0
 *
 *    Unless required by applicable law or agreed to in writing, software
 *    distributed under the License is distributed on an "AS IS" BASIS,
 *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *    See the License for the specific language governing permissions and
 *    limitations under the License.
 */
package org.apache.ibatis.executor;

/**
 * @author Clinton Begin
 */
public class ErrorContext {

  private static final String LINE_SEPARATOR = System.lineSeparator();
  // 创建一个 本地线程的  ErrorContext 对象
  private static final ThreadLocal<ErrorContext> LOCAL = ThreadLocal.withInitial(ErrorContext::new);

  private ErrorContext stored;
  private String resource;
  private String activity;
  private String object;
  private String message;
  private String sql;
  private Throwable cause;

  private ErrorContext() {
  }

  public static ErrorContext instance() {
    return LOCAL.get();
  }

  public ErrorContext store() {
    ErrorContext newContext = new ErrorContext();
    newContext.stored = this;
    LOCAL.set(newContext);
    return LOCAL.get();
  }

  public ErrorContext recall() {
    if (stored != null) {
      LOCAL.set(stored);
      stored = null;
    }
    return LOCAL.get();
  }

  public ErrorContext resource(String resource) {
    this.resource = resource;
    return this;
  }

  public ErrorContext activity(String activity) {
    this.activity = activity;
    return this;
  }

  public ErrorContext object(String object) {
    this.object = object;
    return this;
  }

  public ErrorContext message(String message) {
    this.message = message;
    return this;
  }

  public ErrorContext sql(String sql) {
    this.sql = sql;
    return this;
  }

  public ErrorContext cause(Throwable cause) {
    this.cause = cause;
    return this;
  }

  public ErrorContext reset() {
    resource = null;
    activity = null;
    object = null;
    message = null;
    sql = null;
    cause = null;
    LOCAL.remove();
    return this;
  }

  @Override
  public String toString() {
    StringBuilder description = new StringBuilder();

    // message
    if (this.message != null) {
      description.append(LINE_SEPARATOR);
      description.append("### ");
      description.append(this.message);
    }

    // resource
    if (resource != null) {
      description.append(LINE_SEPARATOR);
      description.append("### The error may exist in ");
      description.append(resource);
    }

    // object
    if (object != null) {
      description.append(LINE_SEPARATOR);
      description.append("### The error may involve ");
      description.append(object);
    }

    // activity
    if (activity != null) {
      description.append(LINE_SEPARATOR);
      description.append("### The error occurred while ");
      description.append(activity);
    }

    // sql
    if (sql != null) {
      description.append(LINE_SEPARATOR);
      description.append("### SQL: ");
      description.append(sql.replace('\n', ' ').replace('\r', ' ').replace('\t', ' ').trim());
    }

    // cause
    if (cause != null) {
      description.append(LINE_SEPARATOR);
      description.append("### Cause: ");
      description.append(cause.toString());
    }

    return description.toString();
  }

}

/**
*
* 单测类
**/
package org.apache.ibatis.exceptions;

import static org.junit.jupiter.api.Assertions.assertEquals;
import static org.junit.jupiter.api.Assertions.assertTrue;

import java.lang.reflect.InvocationTargetException;

import org.apache.ibatis.binding.BindingException;
import org.apache.ibatis.builder.BuilderException;
import org.apache.ibatis.cache.CacheException;
import org.apache.ibatis.datasource.DataSourceException;
import org.apache.ibatis.executor.ExecutorException;
import org.apache.ibatis.logging.LogException;
import org.apache.ibatis.parsing.ParsingException;
import org.apache.ibatis.plugin.PluginException;
import org.apache.ibatis.reflection.ReflectionException;
import org.apache.ibatis.scripting.ScriptingException;
import org.apache.ibatis.session.SqlSessionException;
import org.apache.ibatis.transaction.TransactionException;
import org.apache.ibatis.type.TypeException;
import org.junit.jupiter.api.Test;

class GeneralExceptionsTest {

  private static final String EXPECTED_MESSAGE = "Test Message";
  private static final Exception EXPECTED_CAUSE = new Exception("Nested Exception");

  @Test
  void should() {
    RuntimeException thrown = ExceptionFactory.wrapException(EXPECTED_MESSAGE, EXPECTED_CAUSE);
    assertTrue(thrown instanceof PersistenceException, "Exception should be wrapped in RuntimeSqlException.");
    testThrowException(thrown);
  }
}

这个模块还是比较简单的~

大龄菜鸟-》 mybatis 源码阅读-》 exceptions 异常模块

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