Question

如何获取HttpServletResponse里面的内容

Answer 1

背景：在SPRING 框架之中， 有一个服务端需要提供多种形态的服务，这里的多种形态只是返回值得展示形式（其实 数据内在逻辑完全一样）， 比如：
形式1： JSONP({“key1”: value1, "key2":value2, "key3":value3, ....})
形式2： {“key1”: value1, "key2":value2, "key3":value3, ....}

为了使得后台业务处理代码一样（不做任何区分），现在理由过滤器，对返回接口进行处理，根据需要加上 ：JSONP(...)

主要实现步骤如下：

1. 在web.xml 中配置过滤器
<filter>
<filter-name>RewriteResponse</filter-name>
<filter-class>com.robin.filter.RewriteResponse</filter-class>
</filter>

<filter-mapping>
<filter-name>RewriteResponse</filter-name>
<servlet-name>/*</servlet-name>
</filter-mapping>
// 斜杠星代表匹配任何请求

2. 重点在于RewriteResponse 过滤器

public class RewriteResponseFilter extends Filter {
public String description() {
// TODO Auto-generated method stub
return null;
}
public void doFilter(ServletRequest request, ServletResponse response,
FilterChain chain) throws IOException {
// TODO Auto-generated method stub

ResponseWrapper responseWrapper = new ResponseWrapper((HttpServletResponse) response);
try {
chain.doFilter(request, responseWrapper);
} catch (ServletException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
String responseContent = new String(responseWrapper.getDataStream());
RestResponse fullResponse = new RestResponse(205, "OK-MESSAGE",responseContent);
byte[] responseToSend = restResponseBytes(fullResponse);
response.getOutputStream().write(responseToSend);
}

private byte[] restResponseBytes(RestResponse response) throws IOException {
String serialized = new ObjectMapper().writeValueAsString(response);
return serialized.getBytes("UTF-8");
}
}

3. 通用业务类（用于返回）
public class RestResponse implements Serializable {
private int status;
private String message;

private Object data;
public RestResponse(int status, String message, Object data) {
this.status = status;
this.message = message;
this.data = data;
}

public int getStatus() {
return status;
}
public void setStatus(int status) {
this.status = status;
}
public String getMessage() {
return message;
}
public void setMessage(String message) {
this.message = message;
}
public Object getData() {
return data;
}
public void setData(Object data) {
this.data = data;
}

}

4. 实现ServletOutputStream 指定的扩展
public class FilterServletOutputStream extends ServletOutputStream {

DataOutputStream output;
public FilterServletOutputStream(OutputStream output) {
this.output = new DataOutputStream(output);
}

@Override
public void write(int arg0) throws IOException {
output.write(arg0);
}

@Override
public void write(byte[] arg0, int arg1, int arg2) throws IOException {
output.write(arg0, arg1, arg2);
}

@Override
public void write(byte[] arg0) throws IOException {
output.write(arg0);
}
}

5. 替换原来的输出
public class ResponseWrapper extends HttpServletResponseWrapper {

ByteArrayOutputStream output;
FilterServletOutputStream filterOutput;
HttpResponseStatus status = HttpResponseStatus.OK;

public ResponseWrapper(HttpServletResponse response) {
super(response);
output = new ByteArrayOutputStream();
}

@Override
public ServletOutputStream getOutputStream() throws IOException {
if (filterOutput == null) {
filterOutput = new FilterServletOutputStream(output);
}
return filterOutput;
}

public byte[] getDataStream() {
return output.toByteArray();
}
}