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http://www.yiibai.com/java/io/printwriter_checkerror.htmlhttp://docs.oracle.com/javase/7/docs/api/java/io/PrintWriter.html#checkError()
public boolean checkError()Flushes the stream if it's not closed and checks its error state.Returns:true if the print stream has encountered an error, either on the underlying output stream or during a format conversion.
如果流没有关闭，Flush(从缓存中输出数据并缓存)。然后检查流的错误状态
如果有错误才返回 true
这个应该跟 setError 和 clearError 有关
![[Web front-end] Node.js quick start](https://img.php.cn/upload/course/000/000/067/662b5d34ba7c0227.png)
如果流没有关闭，Flush(从缓存中输出数据并缓存)。然后检查流的错误状态
如果有错误才返回 true
这个应该跟 setError 和 clearError 有关