2 update · J2EE入門實例教程

和上節的思想一樣。我們如下開發： 1. 定制路由 2. 開發C 3. 開發V 4. 測試C與V是否成功對接 5. 開發M 6. 測試M 7. 對接C與M 8. 對接V與C 9. 集成測試在現階段，可以說所有的開發步驟都離不開上述的9步。 # 定制路由 ```  <action name="update" class="teacher.Update"> <result name="success">/jsp/success.jsp</result> <result name="error">/jsp/error.jsp</result> </action> ``` # C ``` package teacher; import entity.Teacher; public class Update { private int id; private String name; private String username; private Boolean sex; private String password; private String email; public int getId() { return id; } public void setId(int id) { this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } public String getUsername() { return username; } public void setUsername(String username) { this.username = username; } public Boolean getSex() { return sex; } public void setSex(String sex) { if (sex.equals("0")) { this.sex = false; } else { this.sex = true; } } public String getPassword() { return password; } public void setPassword(String password) { this.password = password; } public String getEmail() { return email; } public void setEmail(String email) { this.email = email; } // 該execute方法將被自動調用，方法的返回類型必須為String public String execute() { // 獲取要編輯的教師，并實例化 Teacher teacher = new Teacher(id, name, username, email, sex, password); // 打印查看獲取到的信息 System.out.println(teacher.toString()); return "success"; } } ``` # V V層文件，我們仍然使用統一的success.jsp. 已存在。無需更改. # 測試C與V是否成功對接 ![測試](https://box.kancloud.cn/1ad2f21377bd630b321d4145d9029318_549x222.gif) # M ``` public Boolean update() { // 創建會話（這里的session也是會話的意思，我們以前接觸的http中的session，處理的是用戶與服務器的對話） Session session = MysqlJavaee.getCurrentSession(); // 開啟事務（使用緩沖池進行數據庫的連接） Transaction transaction = session.beginTransaction(); // 在這里，必須使用try catch finally語句。來確定會話正常關閉. // 否則，當操作數據庫產生錯誤時，你可能需要重啟mysql服務 try { // 獲取對象 // 使用Teacher.class來獲取到Teacher的類名(包括包名) Teacher teacher = (Teacher) session.get(Teacher.class, id); // 賦值 teacher.setName(name); teacher.setEmail(email); teacher.setPassword(password); teacher.setSex(sex); // 更新 session.update(teacher); // 提交事務 transaction.commit(); // 捕獲異常 } catch (HibernateException e) { // 如果事務執行異常，則回滾事務 if (null != transaction) { transaction.rollback(); } // 打印異常 e.printStackTrace(); } finally { // 如果session處于開啟狀態，則關閉session if (session.isOpen()) { // 關閉會話 session.close(); } } return true; } ``` ## 測試 ``` @Test public void update() { Teacher teacher = Teacher.getTeacherById(1); System.out.println("更新操作前"); System.out.println(teacher.toString()); // 更新 teacher = new Teacher(1, "this is lisi", "zhangsan", "zhangsan@yunzhiclub.com", false, "123"); teacher.update(); // 查看結果 teacher = Teacher.getTeacherById(1); System.out.println("更新操作后"); System.out.println(teacher.toString()); } ``` 我們可以對`(1, "this is zhangsan", "zhangsan", "zhangsan@yunzhiclub.com", false, "123")`的值進行更改，然后執行測試并查看控制臺，同時查看數據表中的數據是否做了更新（初期的時候很重要）. # C對接M ``` // 該execute方法將被自動調用，方法的返回類型必須為String public String execute() { // 獲取要編輯的教師，并實例化 Teacher teacher = new Teacher(id, name, username, email, sex, password); // 更新 teacher.update(); return "success"; } ``` # V對接C ``` // 該execute方法將被自動調用，方法的返回類型必須為String public String execute() { // 獲取要編輯的教師，并實例化 Teacher teacher = new Teacher(id, name, username, email, sex, password); // 更新 teacher.update(); return "success"; } ``` # 集成測試 [http://localhost:8080/javaee/teacher/edit?id=1](http://localhost:8080/javaee/teacher/edit?id=1), 添加數據后點擊submit，查看數據表是否進行更新操作. # 重構代碼如果你前面學習夠扎實的話，相信肯定能夠方法，我們在update()方法中獲取要更新的對象時，是完全可以使用`getTeacherById`來替換`Teacher teacher = (Teacher) session.get(Teacher.class, id);`的。從軟件工程的角度上來講，我們也應該這樣做。原因就不用說了吧：不造相同的輪子. 現在，讓我們修改并測試一下。 ## 代碼修改 ``` // 獲取對象 // 使用Teacher.class來獲取到Teacher的類名(包括包名) Teacher teacher = this.getTeacherById(id); // 賦值 teacher.setName(name); ``` ## 單元測試進行單元測試，我們得到了一個異常: ``` 更新操作前 Teacher [id=1, name=hello, username=zhangsan, email=zhangsan@yunzhiclub.com, sex=false, password=] org.hibernate.TransactionException: nested transactions not supported Hibernate: select teacher0_.id as id1_0_0_, teacher0_.email as email2_0_0_, teacher0_.name as name3_0_0_, teacher0_.password as password4_0_0_, teacher0_.sex as sex5_0_0_, teacher0_.username as username6_0_0_ from Teacher teacher0_ where teacher0_.id=? at org.hibernate.engine.transaction.spi.AbstractTransactionImpl.begin(AbstractTransactionImpl.java:152) at org.hibernate.internal.SessionImpl.beginTransaction(SessionImpl.java:1426) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:498) at org.hibernate.context.internal.ThreadLocalSessionContext$TransactionProtectionWrapper.invoke(ThreadLocalSessionContext.java:352) at com.sun.proxy.$Proxy9.beginTransaction(Unknown Source) at entity.Teacher.getTeacherById(Teacher.java:276) at entity.Teacher.update(Teacher.java:318) at entity.TestTeacher.update(TestTeacher.java:35) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:498) at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:47) at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12) at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:44) at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17) at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:271) at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:70) at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:50) at org.junit.runners.ParentRunner$3.run(ParentRunner.java:238) at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:63) at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:236) at org.junit.runners.ParentRunner.access$000(ParentRunner.java:53) at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:229) at org.junit.runners.ParentRunner.run(ParentRunner.java:309) at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:50) at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:467) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:683) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:390) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:197) 更新操作后 ``` 有說人，老師這怎么看呀，根本抓不住重點。是的，如果把它當成作文來看，當然抓不住重點了。如果抓重點呢？ > 只看自己負責的代碼部分的異常。本著這個思想，我們刪除沒有用的信息后： ``` 更新操作前 Teacher [id=1, name=hello, username=zhangsan, email=zhangsan@yunzhiclub.com, sex=false, password=] org.hibernate.TransactionException: nested transactions not supported at entity.Teacher.getTeacherById(Teacher.java:276) at entity.Teacher.update(Teacher.java:318) at entity.TestTeacher.update(TestTeacher.java:35) ``` 現在異常明朗了。我們知道，自己先執行了TestTeacher.update，然后執行了Teacher.update，再然后執行了：eacher.getTeacherById。看來：異常的輸出順序與執行順序正好相反。把自己的代碼單獨的列出來，最終我們發現，問題出在了Teacher.getTeacherById(Teacher.java:276),我們在控制臺中，單擊跳轉到該行，發現原來是這句:`Transaction transaction = session.beginTransaction();` # BUG產生的原因報的問題是：nested transactions not supported 好的，報錯行找到了，提示找到了，下面我們開始GOOGLE：nested transactions not supported 如果這4個單詞你有不認識的，那么你在GOOGLE前，首先要做的是，去翻譯這行英文為：不支持事務嵌套使用能過查詢我們明白了。他的意思好像是這樣。以下使用正確： ``` 事務開始事務結束事務再開始事務再結束事務再再再開始事務再再再結束 ``` 以下使用錯誤： ``` 事務開始事務開始事務結束事務結束 ``` 找到了錯誤，我們再分析代碼。由于我們在進行session處理里，采用的單例模式。即：張三找我要輔導員，我把王五指定給了他；李四找我要輔導員，我還是給他的王五。所以，在update中，我們已經開啟了事務，而此時，我們又調用getTeacherById方法，當這個方法再開始事務的時候。就出現事務嵌套，最終引發了上述BUG。 # 引用server層徹底解決bug 知道了上述的原因，就不能解決了。由于在數據實體類的方法中，需要使用事務來保證數據操作的安全性。而每個事務都應該是獨立存在，所以在實體中，不能出現互相調用的情況。為了避免這種情況，同時，又不會造相同的輪子。我們增加一個server來解決這個問題。 ## 重構實體 ``` package entity; ... // 聲明主體 @Entity public class Teacher { public Boolean update() { // 創建會話（這里的session也是會話的意思，我們以前接觸的http中的session，處理的是用戶與服務器的對話） Session session = MysqlJavaee.getCurrentSession(); // 開啟事務（使用緩沖池進行數據庫的連接） Transaction transaction = session.beginTransaction(); // 在這里，必須使用try catch finally語句。來確定會話正常關閉. // 否則，當操作數據庫產生錯誤時，你可能需要重啟mysql服務 try { // 更新 session.update(this); // 提交事務 transaction.commit(); // 捕獲異常 } catch (HibernateException e) { // 如果事務執行異常，則回滾事務 if (null != transaction) { transaction.rollback(); } // 打印異常 e.printStackTrace(); } finally { // 如果session處于開啟狀態，則關閉session if (session.isOpen()) { // 關閉會話 session.close(); } } return true; } ... ``` ### 測試 ``` @Test public void update() { Teacher teacher = Teacher.getTeacherById(1); System.out.println("更新操作前"); System.out.println(teacher.toString()); // 更新 teacher.setName("hello1"); teacher.update(); // 查看結果 teacher = Teacher.getTeacherById(1); System.out.println("更新操作后"); System.out.println(teacher.toString()); } ``` 控制臺： ``` 更新操作前 Teacher [id=1, name=hello, username=zhangsan, email=zhangsan@yunzhiclub.com, sex=false, password=] Hibernate: update Teacher set email=?, name=?, password=?, sex=?, username=? where id=? Hibernate: select teacher0_.id as id1_0_0_, teacher0_.email as email2_0_0_, teacher0_.name as name3_0_0_, teacher0_.password as password4_0_0_, teacher0_.sex as sex5_0_0_, teacher0_.username as username6_0_0_ from Teacher teacher0_ where teacher0_.id=? 更新操作后 Teacher [id=1, name=hello1, username=zhangsan, email=zhangsan@yunzhiclub.com, sex=false, password=] Hibernate: select teacher0_.id as id1_0_0_, teacher0_.email as email2_0_0_, teacher0_.name as name3_0_0_, teacher0_.password as password4_0_0_, teacher0_.sex as sex5_0_0_, teacher0_.username as username6_0_0_ from Teacher teacher0_ where teacher0_.id=? Teacher [id=1, name=hello1, username=zhangsan, email=zhangsan@yunzhiclub.com, sex=false, password=] class entity.Teacher ``` ## 建立server包我們在src右建，新建一個package,并起名為server ## 建立TeacherServer文件在package上右建，新建一個class，并起名為TeacherServer,代碼如下： ``` package server; import entity.Teacher; public class TeacherServer { public Boolean update(Teacher newTeacher) { // 獲取數據表數據 Teacher teacher = Teacher.getTeacherById(newTeacher.getId()); // 賦值 teacher.setEmail(newTeacher.getEmail()); teacher.setName(newTeacher.getName()); teacher.setUsername(newTeacher.getUsername()); teacher.setPassword(newTeacher.getPassword()); teacher.setSex(newTeacher.getSex()); // 更新并返回 teacher.update(); return true; } } ``` ### 單元測試同樣，我們在test目錄中，新建一個package, 命名為server，并新建一個TeacherServerTest測試類. 代碼如下： ``` package server; import org.junit.Test; import entity.Teacher; public class TeacherServerTest { @Test public void update() { Teacher teacher = Teacher.getTeacherById(1); System.out.println("更新操作前"); System.out.println(teacher.toString()); // 更新 teacher = new Teacher(1, "this is zhangsan", "zhangsan", "zhangsan@yunzhiclub.com", false, "123"); TeacherServer.update(teacher); // 查看結果 teacher = Teacher.getTeacherById(1); System.out.println("更新操作后"); System.out.println(teacher.toString()); } } ``` 控制臺： ``` 更新操作前 Teacher [id=1, name=hello1, username=zhangsan, email=zhangsan@yunzhiclub.com, sex=false, password=] Hibernate: select teacher0_.id as id1_0_0_, teacher0_.email as email2_0_0_, teacher0_.name as name3_0_0_, teacher0_.password as password4_0_0_, teacher0_.sex as sex5_0_0_, teacher0_.username as username6_0_0_ from Teacher teacher0_ where teacher0_.id=? Hibernate: update Teacher set email=?, name=?, password=?, sex=?, username=? where id=? Hibernate: select teacher0_.id as id1_0_0_, teacher0_.email as email2_0_0_, teacher0_.name as name3_0_0_, teacher0_.password as password4_0_0_, teacher0_.sex as sex5_0_0_, teacher0_.username as username6_0_0_ from Teacher teacher0_ where teacher0_.id=? 更新操作后 Teacher [id=1, name=this is zhangsan, username=zhangsan, email=zhangsan@yunzhiclub.com, sex=false, password=123] ``` ## 對接C層 Update.java ``` // 該execute方法將被自動調用，方法的返回類型必須為String public String execute() { // 獲取要編輯的教師，并實例化 Teacher teacher = new Teacher(id, name, username, email, sex, password); // 更新 TeacherServer.update(teacher); return "success"; } ``` ## 集成測試 [http://localhost:8080/javaee/teacher/edit?id=1](http://localhost:8080/javaee/teacher/edit?id=1)輸入信息后提交，并查看控制臺與數據庫. ** 自下節開始，我們開始拋棄在C層中，直接調用entity的方法。改為C調用server，server再調用entity。** > 本節參考官方文檔：[#objectstate-modifying](https://docs.jboss.org/hibernate/orm/3.3/reference/en/html/objectstate.html#objectstate-modifying)