報錯原因:
當使用 javax.servlet.ServletResponse.getOutputStream() 方法獲取 ServletOutputStream 對象;
又再使用 javax.servlet.ServletResponse.getWriter() 方法獲取 PrintWriter 對象時就會報錯.
源碼片段: 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"));
}
// 當獲取 ServletOutputStream 對象時, 會把 usingOutputStream 成員變量設置爲 true.
usingOutputStream = true;
if (outputStream == null) {
outputStream = new CoyoteOutputStream(outputBuffer);
}
return outputStream;
}
@Override
public PrintWriter getWriter()throws IOException {
// 如果已經通過 getOutputStream() 方法獲取 ServletOutputStream 對象了, 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;
}