【发布时间】：2017-02-07 14:22:07
【问题描述】：
我编写了一个 Java HTTP 响应过滤器，我在其中修改了 HTTP 响应正文。由于我正在更改 HTTP 响应正文，因此我必须根据新内容更新响应中提交的 http content-length 标头。我正在按照以下方式进行操作。
response.setContentLength( next.getBytes().length );
接下来听到的是string
但是，此方法无法设置 HTTP 响应的新内容长度。有人可以建议我在 Java 过滤器中完成它的正确方法是什么
package com.test;
import java.io.BufferedReader;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.CharArrayWriter;
import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.ServletInputStream;
import javax.servlet.ServletOutputStream;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletRequestWrapper;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpServletResponseWrapper;
public class DumpFilter implements Filter {
private static class ByteArrayServletStream extends ServletOutputStream {
ByteArrayOutputStream baos;
ByteArrayServletStream(ByteArrayOutputStream baos) {
this.baos = baos;
}
public void write(int param) throws IOException {
baos.write(param);
}
}
private static class ByteArrayPrintWriter {
private ByteArrayOutputStream baos = new ByteArrayOutputStream();
private PrintWriter pw = new PrintWriter(baos);
private ServletOutputStream sos = new ByteArrayServletStream(baos);
public PrintWriter getWriter() {
return pw;
}
public ServletOutputStream getStream() {
return sos;
}
byte[] toByteArray() {
return baos.toByteArray();
}
}
private class BufferedServletInputStream extends ServletInputStream {
ByteArrayInputStream bais;
public BufferedServletInputStream(ByteArrayInputStream bais) {
this.bais = bais;
}
public int available() {
return bais.available();
}
public int read() {
return bais.read();
}
public int read(byte[] buf, int off, int len) {
return bais.read(buf, off, len);
}
}
private class BufferedRequestWrapper extends HttpServletRequestWrapper {
ByteArrayInputStream bais;
ByteArrayOutputStream baos;
BufferedServletInputStream bsis;
byte[] buffer;
public BufferedRequestWrapper(HttpServletRequest req) throws IOException {
super(req);
InputStream is = req.getInputStream();
baos = new ByteArrayOutputStream();
byte buf[] = new byte[1024];
int letti;
while ((letti = is.read(buf)) > 0) {
baos.write(buf, 0, letti);
}
buffer = baos.toByteArray();
}
public ServletInputStream getInputStream() {
try {
bais = new ByteArrayInputStream(buffer);
bsis = new BufferedServletInputStream(bais);
} catch (Exception ex) {
ex.printStackTrace();
}
return bsis;
}
public byte[] getBuffer() {
return buffer;
}
}
private boolean dumpRequest;
private boolean dumpResponse;
public void init(FilterConfig filterConfig) throws ServletException {
dumpRequest = Boolean.valueOf(filterConfig.getInitParameter("dumpRequest"));
dumpResponse = Boolean.valueOf(filterConfig.getInitParameter("dumpResponse"));
}
public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse,
FilterChain filterChain) throws IOException, ServletException {
final HttpServletRequest httpRequest = (HttpServletRequest)servletRequest;
BufferedRequestWrapper bufferedRequest= new BufferedRequestWrapper(httpRequest);
if (dumpRequest) {
System.out.println("REQUEST -> " + new String(bufferedRequest.getBuffer()));
}
final HttpServletResponse response = (HttpServletResponse) servletResponse;
final ByteArrayPrintWriter pw = new ByteArrayPrintWriter();
HttpServletResponse wrappedResp = new HttpServletResponseWrapper(response) {
public PrintWriter getWriter() {
return pw.getWriter();
}
public ServletOutputStream getOutputStream() {
return pw.getStream();
}
};
filterChain.doFilter(bufferedRequest, wrappedResp);
byte[] bytes = pw.toByteArray();
String s = new String(bytes);
String next = "test message";
response.getOutputStream().write(next.getBytes());
///response.setHeader("Content-Length", String.valueOf(next.length()));
response.setContentLength( next.getBytes().length );
// if (dumpResponse) System.out.println("RESPONSE -> " + s);
}
public void destroy() {}
}
上面给出的是Filter类，但你可能不需要阅读整个类。以下是 doFilter 代码，我在其中修改了 http 正文并设置了内容长度。
public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse,
FilterChain filterChain) throws IOException, ServletException {
final HttpServletRequest httpRequest = (HttpServletRequest)servletRequest;
BufferedRequestWrapper bufferedRequest= new BufferedRequestWrapper(httpRequest);
if (dumpRequest) {
System.out.println("REQUEST -> " + new String(bufferedRequest.getBuffer()));
}
final HttpServletResponse response = (HttpServletResponse) servletResponse;
final ByteArrayPrintWriter pw = new ByteArrayPrintWriter();
HttpServletResponse wrappedResp = new HttpServletResponseWrapper(response) {
public PrintWriter getWriter() {
return pw.getWriter();
}
public ServletOutputStream getOutputStream() {
return pw.getStream();
}
};
filterChain.doFilter(bufferedRequest, wrappedResp);
byte[] bytes = pw.toByteArray();
String s = new String(bytes);
String next = "test message";
response.getOutputStream().write(next.getBytes());
///response.setHeader("Content-Length", String.valueOf(next.length()));
response.setContentLength( next.getBytes().length );
// if (dumpResponse) System.out.println("RESPONSE -> " + s);
}
【问题讨论】：
-
内容长度响应标头描述了响应正文的长度。您遇到什么错误？请发布 servlet 代码。
-
从 PrintWriter 获得的写入器没有设置编码类型的工具，它使用平台所涉及的默认编码。在 mosy 平台上，默认编码为 UTF-16，因此 next.getBytes().length 将返回下一个长度的 2 倍。
标签： java http servlets filter content-length