关于threadLocal用法推荐

package org.apache.ibatis.executor;

/**
 * 错误上下文
 *
 * @author Clinton Begin
 */
public class ErrorContext {

  private static final String LINE_SEPARATOR = System.lineSeparator();

  /**线程级别的缓存，并且初始化创建了{@link 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() {
  }

  /**
   * 获取当前线程中的{@link ErrorContext}对象
   *
   * @return
   */
  public static ErrorContext instance() {
    return LOCAL.get();
  }


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

  /**
   * 重新调用
   * @return
   */
  public ErrorContext recall() {
    if (stored != null) {
      LOCAL.set(stored);
      stored = null;
    }
    return LOCAL.get();
  }

  /**
   * 设置对象的resource属性
   *
   * @param resource
   * @return {@link ErrorContext}
   */
  public ErrorContext resource(String resource) {
    this.resource = resource;
    return this;
  }

  /**
   * 设置对象activity属性
   * @param activity
   * @return
   */
  public ErrorContext activity(String activity) {
    this.activity = activity;
    return this;
  }

  /**
   * 设置对象object属性
   *
   * @param object
   * @return
   */
  public ErrorContext object(String object) {
    this.object = object;
    return this;
  }

  /**
   * 设置对象的message属性
   *
   * @param message
   * @return
   */
  public ErrorContext message(String message) {
    this.message = message;
    return this;
  }

  /**
   * 设置对象的sql属性
   *
   * @param sql
   * @return
   */
  public ErrorContext sql(String sql) {
    this.sql = sql;
    return this;
  }

  /**
   * 设置对象的cause属性
   *
   * @param cause
   * @return
   */
  public ErrorContext cause(Throwable cause) {
    this.cause = cause;
    return this;
  }

  /**
   * 重置
   *
   * @return
   */
  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();
  }

}

BaseStatementHandler

  protected void generateKeys(Object parameter) {
    KeyGenerator keyGenerator = mappedStatement.getKeyGenerator();
    ErrorContext.instance().store();
    keyGenerator.processBefore(executor, mappedStatement, null, parameter);
    ErrorContext.instance().recall();
  }