[HTTP][API] Add backends info API for spark/flink connector (#6984)

Doris should provide a http api to return backends list for connectors to submit stream load,
and without privilege checking, which can let common user to use it

fe/fe-core/src/main/java/org/apache/doris/httpv2/rest/BackendsAction.java

@@ -0,0 +1,112 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+package org.apache.doris.httpv2.rest;
+
+import org.apache.doris.catalog.Catalog;
+import org.apache.doris.httpv2.entity.ResponseEntityBuilder;
+import org.apache.doris.system.Backend;
+
+import com.fasterxml.jackson.annotation.JsonProperty;
+import com.google.common.base.Strings;
+import com.google.common.collect.Lists;
+
+import org.apache.logging.log4j.LogManager;
+import org.apache.logging.log4j.Logger;
+import org.springframework.web.bind.annotation.RequestMapping;
+import org.springframework.web.bind.annotation.RequestMethod;
+import org.springframework.web.bind.annotation.RestController;
+
+import java.util.List;
+import javax.servlet.http.HttpServletRequest;
+import javax.servlet.http.HttpServletResponse;
+
+import lombok.Getter;
+import lombok.Setter;
+
+/**
+ * This class responsible for returning current backends info.
+ * Mainly used for flink/spark connector, which need backends info to execute stream load.
+ * It only requires password, no auth check.
+ * <p>
+ * Response:
+ * <p>
+ * {
+ * "msg": "success",
+ * "code": 0,
+ * "data": {
+ * "backends": [
+ * {
+ * "ip": "192.1.1.1",
+ * "http_port": 8040,
+ * "is_alive": true
+ * }
+ * ]
+ * },
+ * "count": 0
+ * }
+ */
+@RestController
+public class BackendsAction extends RestBaseController {
+    public static final Logger LOG = LogManager.getLogger(BackendsAction.class);
+
+    private static final String IS_ALIVE = "is_alive";
+
+    @RequestMapping(path = "/api/backends", method = {RequestMethod.GET})
+    public Object getBackends(HttpServletRequest request, HttpServletResponse response) {
+        executeCheckPassword(request, response);
+
+        boolean needAlive = false;
+        String isAlive = request.getParameter(IS_ALIVE);
+        if (!Strings.isNullOrEmpty(isAlive) && isAlive.equalsIgnoreCase("true")) {
+            needAlive = true;
+        }
+
+        BackendInfo backendInfo = new BackendInfo();
+        backendInfo.backends = Lists.newArrayList();
+        List<Long> beIds = Catalog.getCurrentSystemInfo().getBackendIds(needAlive);
+        for (Long beId : beIds) {
+            Backend be = Catalog.getCurrentSystemInfo().getBackend(beId);
+            if (be != null) {
+                BackendRow backendRow = new BackendRow();
+                backendRow.ip = be.getHost();
+                backendRow.httpPort = be.getHttpPort();
+                backendRow.isAlive = be.isAlive();
+                backendInfo.backends.add(backendRow);
+            }
+        }
+        return ResponseEntityBuilder.ok(backendInfo);
+    }
+
+    @Getter
+    @Setter
+    public static class BackendInfo {
+        @JsonProperty("backends")
+        public List<BackendRow> backends;
+    }
+
+    @Getter
+    @Setter
+    public static class BackendRow {
+        @JsonProperty("ip")
+        public String ip;
+        @JsonProperty("http_port")
+        public int httpPort;
+        @JsonProperty("is_alive")
+        public boolean isAlive;
+    }
+}