经典的错误，求方案。getOutputStream() has already been called for this response

Question

[code="java"]严重: Servlet.service() for servlet spring-mvc threw exception
java.lang.IllegalStateException: getOutputStream() has already been called for this response[/code]

[code="java"]
严重: Servlet.service() for servlet spring-mvc threw exception
java.lang.IllegalStateException: getOutputStream() has already been called for this response
at org.apache.catalina.connector.Response.getWriter(Response.java:611)
at org.apache.catalina.connector.ResponseFacade.getWriter(ResponseFacade.java:198)
at javax.servlet.ServletResponseWrapper.getWriter(ServletResponseWrapper.java:112)
at org.apache.jasper.runtime.JspWriterImpl.initOut(JspWriterImpl.java:125)
at org.apache.jasper.runtime.JspWriterImpl.flushBuffer(JspWriterImpl.java:118)
at org.apache.jasper.runtime.PageContextImpl.release(PageContextImpl.java:180)[/code]

尝试了网上和多的解决方案 无效！

Answer 1

下面的代码是在实现HTTP协议封装Response时的部分代码
SimpleHttpResponse.java
[code="java"]
OutputStream ops;
PrintWriter writer;
String ce = "utf-8";
public OutputStream getOutputStream() throws Exception {
if(dateType==W)throw new Exception("getWriter() has already been called!");
if(ops==null){
ops = new ByteArrayOutputStream();
dateType = O;
}
return ops;
}
public PrintWriter getWriter() throws Exception {
if(dateType==O)throw new Exception("getOutputStream() has already been called!");
if(writer==null){
ops = new ByteArrayOutputStream();
writer = new PrintWriter(new BufferedWriter(new OutputStreamWriter(ops,ce)),true);
dateType = W;
}
return writer;
}
[/code]
W和O表示已经定义流的模式。
为什么getWriter()之后不能getOutputStream()？或者getOutputStream()之后不能getWriter()呢？
很简单writer是写入字符的，一行写完之后还可能会插入换行回车。显然是不能和outputStream重叠使用。
原理已经给出了，请楼主自己根据实际情况理解错误的原因。