我试图实现从PostgreSQL的ResultSet发送Json的restful服务，我能够通过使用Jersey将mapset映射到POJO类，我不想使用像Gson这样的任何其他库，但是我我希望在没有中间POJO的情况下直接将结果集作为Json发送，因为我不需要POJO用于任何其他目的，我对servlet或restfull或JAXB等不是很熟悉
我能够从ResultSet创建一个自定义的JsonArray（Javax.json）而没有POJO类，并转换为String并在服务上发送String，截至目前为数字，字符串，日期，时间戳（甚至可以尝试为数组做）使用递归，没有写自定义MessageBodyWriter，但可以编写简单的，甚至可能假装甚至为此写作）但是我并不完全理解我做的是否是正确的做法以及如何处理PostgreSQL到Json的所有数据类型并通过Rest发送。
请告诉我有关实施此方法的方法的建议，以及 请评论一些先进的事情，以及它们如何在Jersey，JAXB，JAX-RS上更清楚地相互关联，例如，就像POJO如何在内部转换为Json，哪个是转换的MessageBodyWriter。
请给我关于球衣的建议，而不是其他图书馆。
谢谢。
请找到我写的以下代码，并建议我改进。
资源类：
@Path("/message")
public class MessageResource {
MessageService msgService = new MessageService();
Test t = new Test();
@GET
@Produces(MediaType.TEXT_PLAIN)
public String getMessages() throws SQLException {
return t.getAllMessages();
}
}
服务类：
public class Test {
private static ResultSetMetaData rsmd;
private static int numOfColumns;
PostgreHelper help = new PostgreHelper();
public String getAllMessages() throws SQLException {
RetrieveFromPostGre getData = new RetrieveFromPostGre();
Map<String, ?> config = null;
JsonBuilderFactory factory = Json.createBuilderFactory(config);
JsonObjectBuilder rowJsonObject = factory.createObjectBuilder();
JsonArrayBuilder tableJsonArray = factory.createArrayBuilder();
getData.selectRows("db1", "schema1", "table1");
ResultSet rs = getData.selectRows("db1", "schema1", "table1");
rsmd=rs.getMetaData();
numOfColumns = rsmd.getColumnCount();
try {
while(rs.next()) {
createJsonObjectOfSingleRow(rs, rowJsonObject);
tableJsonArray.add(rowJsonObject);
}
} catch (Exception e) {
System.out.println("error");
}
return tableJsonArray.build().toString();
}
public void createJsonObjectOfSingleRow(ResultSet rs, JsonObjectBuilder rowJsonObject) throws SQLException {
String numberType[] = {"BOOLEAN", "INTEGER", "FLOAT", "LONG", "DOUBLE"};
String stringType[] = {"STRING", "DATE"};
for (int i=1; i<=numOfColumns; i++) {
String column_name = rsmd.getColumnName(i);
System.out.println(help.getDataType(rsmd.getColumnType(i)));
if(Arrays.asList(numberType).contains(help.getDataType(rsmd.getColumnType(i)))) {
System.out.println("in num");
rowJsonObject.add(column_name, rs.getInt(column_name));
}
else if(Arrays.asList(stringType).contains(help.getDataType(rsmd.getColumnType(i)))) {
System.out.println("in stri");
rowJsonObject.add(column_name, rs.getString(column_name));
}
else if(help.getDataType(rsmd.getColumnType(i)).equalsIgnoreCase("ARRAY")) {
/* This is not working, and here I was thinking of doing recursion*/
//System.out.println("in arr");
//JsonArray jArray = (JsonArray) rs.getArray(column_name);
//rowJsonObject.add(column_name, jArray);
rowJsonObject.add("array", "flag");//just for the sake of running code successfully wrote this statement
}
}
}
}
PostgreServices：
public class RetrieveFromPostGre {
PostgreConnection postgreConnection = new PostgreConnection();
PostgreHelper getColumnsMeta = new PostgreHelper();
private String databaseName, schemaName, tableName;
private Map<String, String> columns = new HashMap<String, String>();
public String getDatabaseName() {
return databaseName;
}
public void setDatabaseName(String databaseName) {
this.databaseName = databaseName;
}
public String getSchemaName() {
return schemaName;
}
public void setSchemaName(String schemaName) {
this.schemaName = schemaName;
}
public String getTableName() {
return tableName;
}
public void setTableName(String tableName) {
this.tableName = tableName;
}
public Map<String, String> getColumns() {
return columns;
}
public void setColumns(Map<String, String> columns) {
this.columns = columns;
}
public ResultSet selectRows(String databaseName, String schemaName, String tableName) throws SQLException {
this.setDatabaseName(databaseName);
this.setSchemaName(schemaName);
this.setTableName(tableName);
Connection dbConnection = postgreConnection.getdbconnection(this.getDatabaseName());
ResultSet rs = this.retrieveRows(dbConnection);
return rs;
}
public ResultSet retrieveRows(Connection dbConnection) throws SQLException {
Statement stmt = null;
ResultSet rs = null;
String sql;
sql = "select * from " + this.schemaName + "." + this.tableName;
try {
stmt = dbConnection.createStatement();
rs = stmt.executeQuery(sql);
return rs;
//stmt.close();
} catch (Exception e) {
System.err.println( e.getClass().getName()+": "+ e.getMessage() );
e.printStackTrace();
System.exit(0);
}
return rs;
}
}
DatabaseHelper：
public class PostgreHelper {
public String getDataType(int i) {
String type="";
switch(i) {
case java.sql.Types.INTEGER:
type="INTEGER"; break;
case java.sql.Types.BIGINT:
type="LONG"; break;
case java.sql.Types.BOOLEAN:
type="BOOLEAN"; break;
case java.sql.Types.BIT:
type="BOOLEAN"; break;
case java.sql.Types.FLOAT:
type="FLOAT"; break;
case java.sql.Types.REAL:
type="DOUBLE"; break;
case java.sql.Types.DOUBLE:
type="DOUBLE"; break;
case java.sql.Types.NUMERIC:
type="INTEGER"; break;
case java.sql.Types.DECIMAL:
type="DOUBLE"; break;
case java.sql.Types.CHAR:
type="STRING"; break;
case java.sql.Types.NCHAR:
type="STRING"; break;
case java.sql.Types.VARCHAR:
type="STRING"; break;
case java.sql.Types.NVARCHAR:
type="STRING"; break;
case java.sql.Types.LONGVARCHAR:
type="STRING"; break;
case java.sql.Types.DATE:
type="DATE"; break;
case java.sql.Types.TIME:
type="DATE"; break;
case java.sql.Types.TIMESTAMP:
type="DATE"; break;
case java.sql.Types.BINARY:
type="BINARY"; break;
case java.sql.Types.VARBINARY:
type="BINARY"; break;
case java.sql.Types.LONGVARBINARY:
type="BINARY"; break;
case java.sql.Types.NULL:
type="STRING"; break;
case java.sql.Types.OTHER:
type="STRING"; break;
case java.sql.Types.JAVA_OBJECT:
type="OBJECT"; break;
case java.sql.Types.DISTINCT:
type="STRING"; break;
case java.sql.Types.STRUCT:
type="STRING"; break;
case java.sql.Types.ARRAY:
type="ARRAY"; break;
case java.sql.Types.BLOB:
type="STRING"; break;
case java.sql.Types.CLOB:
type="STRING"; break;
case java.sql.Types.REF:
type="STRING"; break;
}
return type;
}
}
SerializableJSONArray Code，我写这个类代码只是为了知道评论者是否会工作：
public class SerializableJSONArray implements Serializable {
private transient JSONArray jsonArray;
public SerializableJSONArray(JSONArray jsonArray) {
this.jsonArray = jsonArray;
}
public JSONArray getJSONArray() {
return jsonArray;
}
private void writeObject(ObjectOutputStream oos) throws IOException {
oos.defaultWriteObject();
oos.writeObject(jsonArray.toString());
}
private void readObject(ObjectInputStream ois) throws ClassNotFoundException, IOException, JSONException {
ois.defaultReadObject();
jsonArray = new JSONArray((String) ois.readObject());
}
}
答案 0 :(得分：0)
ResultSet不是serializable。你不能将它们直接转换（序列化）为json。
首先需要将ResultSet中所需的值提取到某个可序列化对象，然后再将其转换为json。
答案 1 :(得分：0)
将您的对象存储在地图中，然后将地图转换为json。
以下示例执行此操作，甚至不需要杰克逊。它使用javax.json
public static String toJSON(List<Map<String,String>> maps) {
return javax.json.Json.createArrayBuilder(maps).build().toString();
}