httpmidfetchunchangedfilter.html

用JAVA编写的,在做实验的时候留下来的,本来想删的,但是传上来,大家分享吧

<a name="93" href="#93">93</a>          <em class="comment">// Return FALSE when the document has NOT changed!</em>
<a name="94" href="#94">94</a>          <em class="comment">// Return TRUE if the document has changed or we can't tell</em>
<a name="95" href="#95">95</a>          <strong>if</strong>(o instanceof <a href="../../../../org/archive/crawler/datamodel/CrawlURI.html">CrawlURI</a> == false){
<a name="96" href="#96">96</a>              <em class="comment">// Only handles CrawlURIs</em>
<a name="97" href="#97">97</a>              <strong>if</strong> (logger.isLoggable(Level.INFO)) {
<a name="98" href="#98">98</a>                  logger.info(<span class="string">"Error: Object passed for evaluation was not a "</span> +
<a name="99" href="#99">99</a>                      <span class="string">"CrawlURI. "</span> + o.toString());
<a name="100" href="#100">100</a>             }
<a name="101" href="#101">101</a>             <strong>return</strong> <strong>true</strong>;
<a name="102" href="#102">102</a>         }
<a name="103" href="#103">103</a>         
<a name="104" href="#104">104</a>         <a href="../../../../org/archive/crawler/datamodel/CrawlURI.html">CrawlURI</a> curi = (CrawlURI)o;
<a name="105" href="#105">105</a>         
<a name="106" href="#106">106</a>         <strong>if</strong> (curi.isHttpTransaction() == false) {
<a name="107" href="#107">107</a>             <em class="comment">// Only handles HTTP</em>
<a name="108" href="#108">108</a>             <strong>if</strong> (logger.isLoggable(Level.INFO)) {
<a name="109" href="#109">109</a>                 logger.info(<span class="string">"Error: Non HTTP CrawlURI was passed for evalution. "</span>
<a name="110" href="#110">110</a>                     + curi.toString());
<a name="111" href="#111">111</a>             }
<a name="112" href="#112">112</a>             <strong>return</strong> <strong>true</strong>;
<a name="113" href="#113">113</a>         }
<a name="114" href="#114">114</a>         
<a name="115" href="#115">115</a>         <strong>if</strong>(curi.containsKey(A_HTTP_TRANSACTION) == false){
<a name="116" href="#116">116</a>             <em class="comment">// Missing header info, can't do anything.</em>
<a name="117" href="#117">117</a>             <strong>if</strong> (logger.isLoggable(Level.INFO)) {
<a name="118" href="#118">118</a>                 logger.info(<span class="string">"Error: Missing HttpMethod object in CrawlURI. "</span>
<a name="119" href="#119">119</a>                         + curi.toString());
<a name="120" href="#120">120</a>             }
<a name="121" href="#121">121</a>             <strong>return</strong> <strong>true</strong>;
<a name="122" href="#122">122</a>         }
<a name="123" href="#123">123</a>         
<a name="124" href="#124">124</a>         <em class="comment">// Intially assume header info is missing</em>
<a name="125" href="#125">125</a>         <strong>int</strong> datestamp = HEADER_PREDICTS_MISSING;
<a name="126" href="#126">126</a>         <strong>int</strong> etag = HEADER_PREDICTS_MISSING;
<a name="127" href="#127">127</a>         HttpMethod method = (HttpMethod)curi.getObject(A_HTTP_TRANSACTION);
<a name="128" href="#128">128</a> 
<a name="129" href="#129">129</a>         <em class="comment">// Compare datestamps (last-modified)</em>
<a name="130" href="#130">130</a>         String newDatestamp = <strong>null</strong>;
<a name="131" href="#131">131</a>         <strong>if</strong> (method.getResponseHeader(<span class="string">"last-modified"</span>) != <strong>null</strong>) {
<a name="132" href="#132">132</a>             newDatestamp = method.getResponseHeader(<span class="string">"last-modified"</span>).getValue();
<a name="133" href="#133">133</a>         }
<a name="134" href="#134">134</a>         
<a name="135" href="#135">135</a>         <strong>if</strong> (newDatestamp != <strong>null</strong> &amp;&amp; newDatestamp.length() > 0) {
<a name="136" href="#136">136</a>             datestamp = HEADER_PREDICTS_CHANGED; <em class="comment">// Not missing, assume change</em>
<a name="137" href="#137">137</a>             <strong>if</strong> (curi.containsKey(A_LAST_DATESTAMP)) {
<a name="138" href="#138">138</a>                 <strong>if</strong> (newDatestamp.equals(curi.getString(A_LAST_DATESTAMP))) {
<a name="139" href="#139">139</a>                     <em class="comment">// Both new and old are present and equal, datestamp</em>
<a name="140" href="#140">140</a>                     <em class="comment">// predicts no change</em>
<a name="141" href="#141">141</a>                     datestamp = HEADER_PREDICTS_UNCHANGED;
<a name="142" href="#142">142</a>                 }
<a name="143" href="#143">143</a>             }
<a name="144" href="#144">144</a>             curi.putString(A_LAST_DATESTAMP, newDatestamp);
<a name="145" href="#145">145</a>         }
<a name="146" href="#146">146</a>         
<a name="147" href="#147">147</a>         <em class="comment">// Compare ETags</em>
<a name="148" href="#148">148</a>         String newETag = <strong>null</strong>;
<a name="149" href="#149">149</a>         <strong>if</strong>(method.getResponseHeader(<span class="string">"last-etag"</span>) != <strong>null</strong>){
<a name="150" href="#150">150</a>             newETag = method.getResponseHeader(<span class="string">"last-etag"</span>).getValue();
<a name="151" href="#151">151</a>         }
<a name="152" href="#152">152</a>         
<a name="153" href="#153">153</a>         <strong>if</strong>(newETag != <strong>null</strong> &amp;&amp; newETag.length() > 0){
<a name="154" href="#154">154</a>             etag = HEADER_PREDICTS_CHANGED; <em class="comment">// Not missing, assume change</em>
<a name="155" href="#155">155</a>             <strong>if</strong>(curi.containsKey(A_LAST_ETAG)){
<a name="156" href="#156">156</a>                 <strong>if</strong>(newETag.equals(curi.getString(A_LAST_ETAG))){
<a name="157" href="#157">157</a>                     <em class="comment">// Both new and old are present and equal, etag </em>
<a name="158" href="#158">158</a>                     <em class="comment">// predicts no change</em>
<a name="159" href="#159">159</a>                     etag = HEADER_PREDICTS_UNCHANGED;
<a name="160" href="#160">160</a>                 }
<a name="161" href="#161">161</a>             }
<a name="162" href="#162">162</a>             curi.putString(A_LAST_ETAG, newETag);
<a name="163" href="#163">163</a>         }
<a name="164" href="#164">164</a>         
<a name="165" href="#165">165</a>         <em class="comment">// If both are present, predict no change only if both agree</em>
<a name="166" href="#166">166</a>         <strong>if</strong> (datestamp == HEADER_PREDICTS_UNCHANGED
<a name="167" href="#167">167</a>                 &amp;&amp; etag == HEADER_PREDICTS_UNCHANGED) {
<a name="168" href="#168">168</a>             <em class="comment">// Have both and they agree, no change</em>
<a name="169" href="#169">169</a>             curi.putInt(A_CONTENT_STATE_KEY, CONTENT_UNCHANGED);
<a name="170" href="#170">170</a>             <strong>return</strong> false;
<a name="171" href="#171">171</a>         }
<a name="172" href="#172">172</a>         <em class="comment">// If one or the other is missing, trust the one that is present</em>
<a name="173" href="#173">173</a>         <strong>if</strong> (datestamp == HEADER_PREDICTS_MISSING
<a name="174" href="#174">174</a>                 &amp;&amp; etag == HEADER_PREDICTS_UNCHANGED) {
<a name="175" href="#175">175</a>             <em class="comment">// Only have etag, and it predicts no change</em>
<a name="176" href="#176">176</a>             curi.putInt(A_CONTENT_STATE_KEY, CONTENT_UNCHANGED);
<a name="177" href="#177">177</a>             <strong>return</strong> false;
<a name="178" href="#178">178</a>         }
<a name="179" href="#179">179</a>         <strong>if</strong> (datestamp == HEADER_PREDICTS_UNCHANGED
<a name="180" href="#180">180</a>                 &amp;&amp; etag == HEADER_PREDICTS_MISSING) {
<a name="181" href="#181">181</a>             <em class="comment">// Only have last-modified, and it predicts no change</em>
<a name="182" href="#182">182</a>             curi.putInt(A_CONTENT_STATE_KEY, CONTENT_UNCHANGED);
<a name="183" href="#183">183</a>             <strong>return</strong> false;
<a name="184" href="#184">184</a>         }
<a name="185" href="#185">185</a>         <strong>return</strong> <strong>true</strong>; <em class="comment">// Default, assume change. </em>
<a name="186" href="#186">186</a>     }
<a name="187" href="#187">187</a> }
</pre>
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