HttpClient: Content-Length header already present解决及分析

快来打我* 2023-06-16 02:22 16阅读 0赞

在用HttpClient的时候出现如下问题：

org.apache.http.client.ClientProtocolException
    at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:822)
    at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:754)
    at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:732)
    ……
    Caused by: org.apache.http.ProtocolException: Content-Length header already present
    at org.apache.http.protocol.RequestContent.process(RequestContent.java:67)
    at org.apache.http.protocol.ImmutableHttpProcessor.process(ImmutableHttpProcessor.java:108)
    at org.apache.http.protocol.HttpRequestExecutor.preProcess(HttpRequestExecutor.java:174)
    at org.apache.http.impl.client.DefaultRequestDirector.execute(DefaultRequestDirector.java:462)
    at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:820)
    ... 27 more

*  出现上面的问题是发送请求的时候设置了请求头`Content-Length`参数。
 *  解决办法：把设置的请求头`Content-Length`参数去掉。
 *  分析原因：  
    跟踪代码:查看HttpClient中RequestContent类的process方法，看到当body非空时，会自动加上Content-Length请求头及其对应值，不需要自己手动加上它。加上就会抛出上面的异常。  
    源码：

public class RequestContent implements HttpRequestInterceptor { 
        private final boolean overwrite;
    
        public RequestContent() { 
            this(false);
        }
    
        public RequestContent(boolean overwrite) { 
            this.overwrite = overwrite;
        }
    
        public void process(HttpRequest request, HttpContext context) throws HttpException, IOException { 
            Args.notNull(request, "HTTP request");
            if (request instanceof HttpEntityEnclosingRequest) { 
                if (this.overwrite) { 
                    request.removeHeaders("Transfer-Encoding");
                    request.removeHeaders("Content-Length");
                } else { 
                    if (request.containsHeader("Transfer-Encoding")) { 
                        throw new ProtocolException("Transfer-encoding header already present");
                    }
    
                    if (request.containsHeader("Content-Length")) { 
                        throw new ProtocolException("Content-Length header already present");
                    }
                }
    
                ProtocolVersion ver = request.getRequestLine().getProtocolVersion();
                HttpEntity entity = ((HttpEntityEnclosingRequest)request).getEntity();
                if (entity == null) { 
                    request.addHeader("Content-Length", "0");
                    return;
                }
    
                if (!entity.isChunked() && entity.getContentLength() >= 0L) { 
                	//计算请求头的长度
                    request.addHeader("Content-Length", Long.toString(entity.getContentLength()));
                } else { 
                    if (ver.lessEquals(HttpVersion.HTTP_1_0)) { 
                        throw new ProtocolException("Chunked transfer encoding not allowed for " + ver);
                    }
    
                    request.addHeader("Transfer-Encoding", "chunked");
                }
    
                if (entity.getContentType() != null && !request.containsHeader("Content-Type")) { 
                    request.addHeader(entity.getContentType());
                }
    
                if (entity.getContentEncoding() != null && !request.containsHeader("Content-Encoding")) { 
                    request.addHeader(entity.getContentEncoding());
                }
            }
    
        }
    }