java.lang.IllegalStateException: getOutputStream() has already been called for this response

最新推荐文章于 2023-08-11 14:37:08 发布

原创最新推荐文章于 2023-08-11 14:37:08 发布 · 1.2k 阅读

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#org.apache.catalina.connector. #java.lang.IllegalStateExceptio #getOutputStream() has already

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本文详细解释了在Java Servlet中，同时使用ServletResponse.getOutputStream()和ServletResponse.getWriter()方法时引发的错误原因。介绍了这两种方法如何分别控制二进制数据和字符数据的输出，并探讨了它们之间的互斥机制。

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报错原因:

当使用 javax.servlet.ServletResponse.getOutputStream() 方法获取 ServletOutputStream 对象;

又再使用 javax.servlet.ServletResponse.getWriter() 方法获取 PrintWriter 对象时就会报错.

源码片段: org.apache.catalina.connector.Response


/** Using output stream flag. **/
protected boolean usingOutputStream = false;

@Override
public ServletOutputStream getOutputStream()throws IOException {
	if (usingWriter) {
		throw new IllegalStateException(sm.getString("coyoteResponse.getOutputStream.ise"));
	}
    // 当获取 ServletOutputStream 对象时, 会把 usingOutputStream 成员变量设置为 true.
	usingOutputStream = true;
	if (outputStream == null) {
		outputStream = new CoyoteOutputStream(outputBuffer);
	}
	return outputStream;
}

@Override
public PrintWriter getWriter()throws IOException {
	// 如果已经通过 getOutputStream() 方法获取 ServletOutputStream 对象了, usingOutputStream = true
	if (usingOutputStream) {
		throw new IllegalStateException(sm.getString("coyoteResponse.getWriter.ise"));
	}
	
	if (ENFORCE_ENCODING_IN_GET_WRITER) {
		/*
		* If the response's character encoding has not been specified as
		* described in <code>getCharacterEncoding</code> (i.e., the method
		* just returns the default value <code>ISO-8859-1</code>),
		* <code>getWriter</code> updates it to <code>ISO-8859-1</code>
		* (with the effect that a subsequent call to getContentType() will
		* include a charset=ISO-8859-1 component which will also be
		* reflected in the Content-Type response header, thereby satisfying
		* the Servlet spec requirement that containers must communicate the
		* character encoding used for the servlet response's writer to the
		* client).
		*/
		setCharacterEncoding(getCharacterEncoding());
	}
	usingWriter = true;
	outputBuffer.checkConverter();
	if (writer == null) {
		writer = new CoyoteWriter(outputBuffer);
	}
	return writer;
}