java爬蟲第一天-bug記錄

注意：實現爬蟲要使用idea自帶的maven。
bug1：

Cannot resolve symbol 'response'

原因：

try {
             CloseableHttpResponse response = httpClient.execute(httpGet);

            if(response.getStatusLine().getStatusCode() == 200) {
                String content = EntityUtils.toString(response.getEntity() , "utf-8");
                System.out.println(content.length());
            }
        } catch (IOException e) {
            e.printStackTrace();
        }finally {
            try {
                response.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
            try {
                httpClient.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }

解決辦法：

 CloseableHttpResponse response = null;
        try {
             response = httpClient.execute(httpGet);

            if(response.getStatusLine().getStatusCode() == 200) {
                String content = EntityUtils.toString(response.getEntity() , "utf-8");
                System.out.println(content.length());
            }
        } catch (IOException e) {
            e.printStackTrace();
        }finally {
            try {
                response.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
            try {
                httpClient.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }

bug2：

org.apache.http.client.ClientProtocolException
	at org.apache.http.impl.client.InternalHttpClient.doExecute(InternalHttpClient.java:187)
	at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:83)
	at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:108)
	at cn.itcast.crawler.test.HttpGetTest.main(HttpGetTest.java:21)
Caused by: org.apache.http.ProtocolException: Target host is not specified
	at org.apache.http.impl.conn.DefaultRoutePlanner.determineRoute(DefaultRoutePlanner.java:71)
	at org.apache.http.impl.client.InternalHttpClient.determineRoute(InternalHttpClient.java:125)
	at org.apache.http.impl.client.InternalHttpClient.doExecute(InternalHttpClient.java:184)
	... 3 more
Exception in thread "main" java.lang.NullPointerException
	at cn.itcast.crawler.test.HttpGetTest.main(HttpGetTest.java:31)

原因：

CloseableHttpClient httpClient = HttpClients.createDefault();
        HttpGet httpGet = new HttpGet("");
        CloseableHttpResponse response = null;
        try {
             response = httpClient.execute(httpGet);

            if(response.getStatusLine().getStatusCode() == 200) {
                String content = EntityUtils.toString(response.getEntity() , "utf-8");
                System.out.println(content.length());
            }
        } catch (IOException e) {
            e.printStackTrace();
        }

解決辦法：

CloseableHttpClient httpClient = HttpClients.createDefault();
        HttpGet httpGet = new HttpGet("http://www.itcast.cn");
        CloseableHttpResponse response = null;
        try {
             response = httpClient.execute(httpGet);

            if(response.getStatusLine().getStatusCode() == 200) {
                String content = EntityUtils.toString(response.getEntity() , "utf-8");
                System.out.println(content.length());
            }
        } catch (IOException e) {
            e.printStackTrace();
        }

bug3:註釋掉test仍看不到日誌輸出。

log4j:WARN No appenders could be found for logger (org.apache.http.client.protocol.RequestAddCookies).
log4j:WARN Please initialize the log4j system properly.
log4j:WARN See http://logging.apache.org/log4j/1.2/faq.html#noconfig for more info.

</dependency>
        <!-- https://mvnrepository.com/artifact/org.slf4j/slf4j-log4j12 -->
        <dependency >
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-log4j12</artifactId>
            <version>1.7.25</version>
<!--            <scope>test</scope>-->
        </dependency>

解決：
因為1.2版本的要在 log4j.properties 檔案裡配置輸出

# Global logging configuration 這個配置是除錯用的配置，生產環境要改成INFO或更高階別
log4j.rootLogger=DEBUG, stdout
# Console output...
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern= %-d{yyyy-MM-dd HH:mm:ss} [ %t:%r ] - [ %p ] %m%n

原始碼：

package cn.itcast.crawler.test;

import org.apache.http.client.methods.CloseableHttpResponse;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.util.EntityUtils;

import java.io.IOException;


public class HttpGetTest {
    public static void main(String[] args)  {
        CloseableHttpClient httpClient = HttpClients.createDefault();
        HttpGet httpGet = new HttpGet("http://www.itcast.cn");
        CloseableHttpResponse response = null;
        try {
            response = httpClient.execute(httpGet);

            if(response.getStatusLine().getStatusCode() == 200) {
                String content = EntityUtils.toString(response.getEntity() , "utf-8");
                System.out.println(content.length());
            }
        } catch (IOException e) {
            e.printStackTrace();
        }finally {
            try {
                response.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
            try {
                httpClient.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }


    }
}