1、场景
1.1、依赖版本
- avatica-core 1.11.0
- druid 0.12.0
1.2、问题重现：
使用Avatica JDBC查询语句：SELECT score FROM student WHERE name='小明'
到Druid变成：SELECT score FROM student WHERE name='??'。
2、解决过程
思路：检查请求发送前request body -> 检查收到请求后解析的文本
2.1、初步怀疑请求编码所致
初步怀疑请求的编码格式设置不正确。为了方便查看返回的结果是否是乱码，我们使用EXPLAIN PLAN FOR来调试。查看请求日志，可以知道avatica的内部使用了HttpClient实现的。
17:45:17.557 [main] DEBUG org.apache.http.headers - http-outgoing-0 >> POST /druid/v2/sql/avatica/ HTTP/1.1
17:45:17.557 [main] DEBUG org.apache.http.headers - http-outgoing-0 >> Content-Length: 241
17:45:17.557 [main] DEBUG org.apache.http.headers - http-outgoing-0 >> Content-Type: application/octet-stream
17:45:17.557 [main] DEBUG org.apache.http.headers - http-outgoing-0 >> Host: localhost:8082
17:45:17.557 [main] DEBUG org.apache.http.headers - http-outgoing-0 >> Connection: Keep-Alive
17:45:17.557 [main] DEBUG org.apache.http.headers - http-outgoing-0 >> User-Agent: Apache-HttpClient/4.5.3 (Java/1.8.0_131)
17:45:17.557 [main] DEBUG org.apache.http.headers - http-outgoing-0 >> Accept-Encoding: gzip,deflate
17:45:17.557 [main] DEBUG org.apache.http.wire - http-outgoing-0 >> "POST /druid/v2/sql/avatica/ HTTP/1.1[
][
]"
17:45:17.557 [main] DEBUG org.apache.http.wire - http-outgoing-0 >> "Content-Length: 241[
][
]"
17:45:17.557 [main] DEBUG org.apache.http.wire - http-outgoing-0 >> "Content-Type: application/octet-stream[
][
]"
17:45:17.557 [main] DEBUG org.apache.http.wire - http-outgoing-0 >> "Host: localhost:8082[
][
]"
17:45:17.557 [main] DEBUG org.apache.http.wire - http-outgoing-0 >> "Connection: Keep-Alive[
][
]"
17:45:17.557 [main] DEBUG org.apache.http.wire - http-outgoing-0 >> "User-Agent: Apache-HttpClient/4.5.3 (Java/1.8.0_131)[
][
]"
17:45:17.557 [main] DEBUG org.apache.http.wire - http-outgoing-0 >> "Accept-Encoding: gzip,deflate[
][
]"
17:45:17.557 [main] DEBUG org.apache.http.wire - http-outgoing-0 >> "[
][
]"
17:45:17.557 [main] DEBUG org.apache.http.wire - http-outgoing-0 >> "{"request":"prepareAndExecute","connectionId":"b4490330-c1c1-493a-b40d-a4303698cafa","statementId":1,"sql":"EXPLAIN PLAN FOR SELECT score FROM student WHERE name='[0xe6][0xb4][0x97][0xe5]'","maxRowsInFirstFrame":-1,"maxRowCount":-1}"
可以发现请求的sqlEXPLAIN PLAN FOR SELECT score FROM student WHERE name='小明'发送时变成了EXPLAIN PLAN FOR SELECT score FROM student WHERE name='[0xe6][0xb4][0x97][0xe5]'，这是编码乱了吗？其实不是的，我们可以通过指定avatica的HttpClient，来调试请求发送前的数据。
通过复制avatica-core-1.11.0.jar的AvaticaCommonsHttpClientImpl类，改变public byte[] send(byte[] request)的实现，可以改变请求的方式。
同时jdbc调用的时候指定httpclient_impl，即可。
String url = "jdbc:avatica:remote:url=http://localhost:8082/druid/v2/sql/avatica/";
Properties connectionProperties = new Properties();
connectionProperties.setProperty("httpclient_impl", "com.test.MyAvaticaCommonsHttpClientImpl");
conn = DriverManager.getConnection(url, connectionProperties);
最后无论怎么改变send方法的实现，最后返回的结果始终带有??。
17:45:18.907 [main] DEBUG org.apache.http.wire - http-outgoing-0 << "HTTP/1.1 200 OK[
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]"
17:45:18.908 [main] DEBUG org.apache.http.wire - http-outgoing-0 << "Date: Tue, 15 May 2018 09:45:30 GMT[
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]"
17:45:18.908 [main] DEBUG org.apache.http.wire - http-outgoing-0 << "Content-Type: application/json;charset=utf-8[
][
]"
17:45:18.908 [main] DEBUG org.apache.http.wire - http-outgoing-0 << "Content-Length: 1641[
][
]"
17:45:18.908 [main] DEBUG org.apache.http.wire - http-outgoing-0 << "Server: Jetty(9.3.19.v20170502)[
][
]"
17:45:18.908 [main] DEBUG org.apache.http.wire - http-outgoing-0 << "[
][
]"
17:45:18.909 [main] DEBUG org.apache.http.wire - http-outgoing-0 << "{"response":"executeResults","missingStatement":false,"rpcMetadata":{"response":"rpcMetadata","serverAddress":"master:8082"},"results":[{"response":"resultSet","connectionId":"b4490330-c1c1-493a-b40d-a4303698cafa","statementId":1,"ownStatement":false,"signature":{"columns":[{"ordinal":0,"autoIncrement":false,"caseSensitive":true,"searchable":false,"currency":false,"nullable":0,"signed":true,"displaySize":-1,"label":"PLAN","columnName":"PLAN","schemaName":null,"precision":-1,"scale":-2147483648,"tableName":null,"catalogName":null,"type":{"type":"scalar","id":12,"name":"VARCHAR","rep":"STRING"},"readOnly":true,"writable":false,"definitelyWritable":false,"columnClassName":"java.lang.String"}],"sql":"EXPLAIN PLAN FOR SELECT score FROM student WHERE name='??'","parameters":[],"cursorFactory":{"style":"LIST","clazz":null,"fieldNames":null},"statementType":"SELECT"},"firstFrame":{"offset":0,"done":true,"rows":[["DruidQueryRel(query=[{"queryType":"scan","dataSource":{"type":"table","name":"student"},"intervals":{"type":"intervals","intervals":["-146136543-09-08T08:23:32.096Z/146140482-04-24T15:36:27.903Z"]},"virtualColumns":[],"resultFormat":"compactedList","batchSize":20480,"filter":{"type":"selector","dimension":"name","value":"??","extractionFn":null},"columns":["score"],"legacy":false,"context":{},"descending":false,"granularity":{"type":"all"}}], signature=[{name:STRING])
"]]},"updateCount":-1,"rpcMetadata":{"response":"rpcMetadata","serverAddress":"master:8082"}}]}[
]"
17:45:18.910 [main] DEBUG org.apache.http.headers - http-outgoing-0 << HTTP/1.1 200 OK
17:45:18.910 [main] DEBUG org.apache.http.headers - http-outgoing-0 << Date: Tue, 15 May 2018 09:45:30 GMT
17:45:18.911 [main] DEBUG org.apache.http.headers - http-outgoing-0 << Content-Type: application/json;charset=utf-8
17:45:18.911 [main] DEBUG org.apache.http.headers - http-outgoing-0 << Content-Length: 1641
17:45:18.911 [main] DEBUG org.apache.http.headers - http-outgoing-0 << Server: Jetty(9.3.19.v20170502)
2.2、检查Druid收到的请求以及返回
既然检查发送前的请求没问题，那么接下来检查请求接收后的情况。
通过全局搜索Druid的源码，搜索/druid/v2/sql/avatica/，可以知道我们刚才的请求被DruidAvaticaHandler类接收并处理，最后实际处理的avatica-server，而这里用的是1.10.0版本，通过版本对比，没版本的问题。
通过检查avatica-server的AvaticaJsonHandler类的方法：
public void handle(String target, Request baseRequest, HttpServletRequest request, HttpServletResponse response)
看到不和谐的地方：
final String jsonRequest = new String(rawRequest.getBytes("ISO-8859-1"), "UTF-8");,
UTF-8编码传来的请求居然用ISO-8859-1转换？原来问题就出现在这里。
3、解决方法
3.1、修改avatica-server源码
上github克隆avatica-server 1.10.0的代码，找到AvaticaJsonHandler类的方法：
public void handle(String target, Request baseRequest, HttpServletRequest request, HttpServletResponse response)
修改：
final String jsonRequest = new String(rawRequest.getBytes("ISO-8859-1"), "UTF-8");
=> final String jsonRequest = new String(rawRequest.getBytes("UTF-8"), "UTF-8");
3.2、重新编译avatica-server
运行clean install -Dmaven.test.skip=true -Dcheckstyle.skip=true，重新生成avatica-server的jar
3.3、覆盖Druid的依赖
上Druid所在的服务器，进入lib，把avatica-server-1.10.0.jar备份并覆盖，重启服务。
编译好的jar包下载：https://download.csdn.net/download/yongjian_pan/10417162