servlet初始化方法無法創建mysql表-為什么？

Question

我的Java Servlet初始化方法無法創建mysql表-我想知道為什么。 當我直接登錄mysql並創建表時，生活很美好，當我刪除表並運行servlet時-沒有表，servlet會拋出一個異常（尚未完全挖掘出來）。代碼如下所示：

package ...;
import ... // quite a bit
@WebServlet("/MyClass") 
public class MyClass extends HttpServlet {
          public void init() throws ServletException {
        try {     Foo foo = Foo.getInstance();
                    foo.createTables();  
            } catch (Exception e) {
                throw new ServletException("Error creating tables", e);         
            }
      }

... //更多MyClass的東西} // Foo是一個單例，看起來像這樣：

    package ...;
    import ... // quite a bit
public class Foo {
  public static final Foo INSTANCE = new Foo();

  public static Foo getInstance() {
    return INSTANCE;
  } 

... //更多Foo的東西，然后

public void createTables(){
 try {

        // first establish a connection
 Connection connection = Foo.getInstance().getConnection(); // get connection est.

//與dbase的est連接-設置表后，效果很好

 //Create a query. 
 Statement stmt = connection.createStatement(); 

    String query = "CREATE TABLE IF NOT EXISTS survey (uuid_Survey VARCHAR(36) NOT NULL, "+
    "top VARCHAR(40), " +
    " likert VARCHAR(40), "+
    " numerical VARCHAR(40), "+
    " open VARCHAR(40), " +
    " KEY ix_survey_uuid (uuid_Survey), "+
    " PRIMARY KEY (uuid_Survey))";

 ResultSet rs = stmt.executeQuery( query ); 
     query = "CREATE TABLE IF NOT EXISTS result (" +
    "uuid_Survey VARCHAR(36) NOT NULL, "+
    "remoteAddress VARCHAR(15) NOT NULL, " +
    "currentTime BIGINT NOT NULL, "+
    " likert VARCHAR(40),"+
    " numerical DOUBLE, " +
    " open VARCHAR(40),  "+
    " PRIMARY KEY (uuid_Survey, remoteAddress, currentTime),"+
    "FOREIGN KEY ix_survey_uuid (uuid_Survey) REFERENCES survey (uuid_Survey))" ;

 rs = stmt.executeQuery( query );  

 connection.close();

 } catch (Exception e) {
        System.err.println("Error creating tables: " + e);
 }

 }

Answer 1

您不能使用stmt.executeQuery( query );

正如醫生所說-

ResultSet#executeQuery(String sql) -此方法執行給定的SQL語句，該語句返回單個ResultSet對象。 其中sql-要發送到數據庫的SQL語句，通常是靜態SQL SELECT語句

您可能想使用execute（）代替

像stmt.execute(query);

要么

String query = "CREATE TABLE IF NOT EXISTS survey (uuid_Survey VARCHAR(36) NOT NULL,"+
        "top VARCHAR(40), " +
        " likert VARCHAR(40), "+
        " numerical VARCHAR(40), "+
        " open VARCHAR(40), " +
        " KEY ix_survey_uuid (uuid_Survey), "+
        " PRIMARY KEY (uuid_Survey))";
PreparedStatement statement = conn.prepareStatement(query);
int count = statement.executeUpdate();
if(count>=0){
    System.out.println("Successfully created.");
}