mget(可以通过索引、类型、或ID一次得到同一索引或不同索引库里的文档集合) & mapping

使用multi get API可以通过索引名、类型名、文档id一次得到一个文档集合，文档可以来自同一个索引库，也可以来自不同索引库。示例如下:

MultiGetResponse multiGetItemResponses = client.prepareMultiGet()
.add("twitter", "tweet", "1")    //注释1
.add("twitter", "tweet", "2", "3", "4")     //注释2
.add("another", "type", "foo")          //注释3
.get();

for (MultiGetItemResponse itemResponse : multiGetItemResponses) {       //注释4
GetResponse response = itemResponse.getResponse();
if (response.isExists()) {                   //注释5
String json = response.getSourceAsString();    //注释6
}
}

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注释1: 通过单一的ID获取一个文档. 

注释2：传入多个id，从相同的索引名/类型名中获取多个文档. 

注释3：可以同时获取不同索引中的文档. 

注释4：遍历结果集. 

注释5：检验文档是否存在. 

注释6：获取文档源.

一、获取索引的所有mapping

通过java客户端获取mapping：

package elasticsearch.in.action.client;

import java.net.InetAddress;
import java.net.UnknownHostException;

import org.elasticsearch.client.transport.TransportClient;
import org.elasticsearch.cluster.metadata.MappingMetaData;
import org.elasticsearch.common.collect.ImmutableOpenMap;
import org.elasticsearch.common.settings.Settings;
import org.elasticsearch.common.transport.InetSocketTransportAddress;

public class TransClient {
public static String clusterName = "elasticsearch";// 集群名称
public static String serverIP = "127.0.0.1";// 服务器IP
public static void main(String[] args) {
System.out.println(getMapping("news", "sportnews"));
}

public static String getMapping(String indexname, String typename) {
Settings settings = Settings.settingsBuilder().put("cluster.name", clusterName).build();
String mapping="";
try {
TransportClient client = TransportClient.builder().settings(settings).build()
.addTransportAddress(new InetSocketTransportAddress(InetAddress.getByName(serverIP), 9300));

ImmutableOpenMap<String, MappingMetaData> mappings = client.admin().cluster().prepareState().execute()
.actionGet().getState().getMetaData().getIndices().get(indexname).getMappings();
mapping = mappings.get(typename).source().toString();

client.close();
} catch (UnknownHostException e) {
e.printStackTrace();
}

return mapping;
}

}

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二、获取所有的type以及每个type的mapping

mapping信息都是ImmutableOpenMap

for (ObjectObjectCursor<String, MappingMetaData> cursor : mappings) {
System.out.println(cursor.key); // 索引下的每个type
System.out.println(cursor.value.getSourceAsMap()); // 每个type的mapping
}