Java - cocher si ServletResponse a n'importe quel contenu - Stack Overflow

How can I check if a response (ServletResponse) contains any content without calling the getWriter() - method, e. g. in a filter? Or in other words: the filter should only modify the content if there was already written something into the stream:

public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
    // Only do that if there is really some content
    PrintWriter out = response.getWriter();

It could happen that the response.getWriter() - method might be called later on somewhere else in the code (not in this filter, e. g. for a file-download). In that case, the second call will fail since the stream was already opened...

One way is to extend ServletResponseWrapper and use a CharArrayWriter internally for writing the response. The CharArrayWriter has a size() method which will return the size of the buffer. Make sure you pass a wrapped response down the filter chain and you should be able to get the size at any point in the program.

public class LengthAwareServletResponseWrapper extends ServletResponseWrapper {

    private final CharArrayWriter out = new CharArrayWriter();

    public LengthAwareServletResponseWrapper(final ServletResponse response) {
        super(response);
    }

    public int getWrittenContentLength() {
        return out.size();
    }

    @Override
    public PrintWriter getWriter() throws IOException {
        return new PrintWriter(out);
    }
}

How can I check if a response (ServletResponse) contains any content without calling the getWriter() - method, e. g. in a filter? Or in other words: the filter should only modify the content if there was already written something into the stream:

public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
    // Only do that if there is really some content
    PrintWriter out = response.getWriter();

It could happen that the response.getWriter() - method might be called later on somewhere else in the code (not in this filter, e. g. for a file-download). In that case, the second call will fail since the stream was already opened...

One way is to extend ServletResponseWrapper and use a CharArrayWriter internally for writing the response. The CharArrayWriter has a size() method which will return the size of the buffer. Make sure you pass a wrapped response down the filter chain and you should be able to get the size at any point in the program.

public class LengthAwareServletResponseWrapper extends ServletResponseWrapper {

    private final CharArrayWriter out = new CharArrayWriter();

    public LengthAwareServletResponseWrapper(final ServletResponse response) {
        super(response);
    }

    public int getWrittenContentLength() {
        return out.size();
    }

    @Override
    public PrintWriter getWriter() throws IOException {
        return new PrintWriter(out);
    }
}

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