JPA J2SE 桌面应用范例
JPA虽然是Java EE规范的一部分，但是可以在J2SE环境下单独使用，不需要Web相关容器。本篇主要通过Netbeans 自动生成的代码来学习JPA相关内容。
1.打开Netbeans 8.1 添加Mysql数据库连接
2.新建Java应用程式，输入项目名称JpaExample
3.在项目中右键新建其他，选择主样例窗体/详细样例窗体，输入类名称和包名称
4.选择第一步建立的数据库连接->选择表(user)，右侧为程式中用到的栏位，默认是全部带到右边，不需要的可以移到左边
5.选择在Swing界面上显示的栏位，默认全部在右边表示全选，不需要的可以移到左边。点击完成
6.查看生成的类，persistence.xml是jpa配置文件，User.java是对于table的实体，MasterDetailForm.java是自动生成的Swing界面，自动添加的库文件包括实现JPA2.1 的EclipseLink和添加连接mysql数据库的jdbc驱动，都是安装Netbeans自带的可以自行替换指定版本。
7.运行，点击New就可以新增内容，Delete删除上面Jtable选中的数据，Save保存到数据库，Refresh 刷新数据，主要是数据库数据与JPA同步，如果数据库有变动，刷新后本地JPA显示变动后数据。
8.代码分析,完整MasterDetailForm.java如下。
package com.cc.jpa; import java.awt.EventQueue; import java.beans.Beans; import java.util.ArrayList; import java.util.List; import javax.persistence.RollbackException; import javax.swing.JFrame; import javax.swing.JPanel; /** * * @author dev */ public class MasterDetailForm extends JPanel { public MasterDetailForm() { initComponents(); if (!Beans.isDesignTime()) { entityManager.getTransaction().begin(); } } /** * This method is called from within the constructor to initialize the form. * WARNING: Do NOT modify this code. The content of this method is always * regenerated by the Form Editor. */ @SuppressWarnings("unchecked") // <editor-fold defaultstate="collapsed" desc="Generated Code"> private void initComponents() { bindingGroup = new org.jdesktop.beansbinding.BindingGroup(); entityManager = java.beans.Beans.isDesignTime() ? null : javax.persistence.Persistence.createEntityManagerFactory("ccPU").createEntityManager(); query = java.beans.Beans.isDesignTime() ? null : entityManager.createQuery("SELECT u FROM User u"); list = java.beans.Beans.isDesignTime() ? java.util.Collections.emptyList() : org.jdesktop.observablecollections.ObservableCollections.observableList(query.getResultList()); masterScrollPane = new javax.swing.JScrollPane(); masterTable = new javax.swing.JTable(); idLabel = new javax.swing.JLabel(); usernmaeLabel = new javax.swing.JLabel(); passwordLabel = new javax.swing.JLabel(); nameLabel = new javax.swing.JLabel(); idField = new javax.swing.JTextField(); usernmaeField = new javax.swing.JTextField(); passwordField = new javax.swing.JTextField(); nameField = new javax.swing.JTextField(); saveButton = new javax.swing.JButton(); refreshButton = new javax.swing.JButton(); newButton = new javax.swing.JButton(); deleteButton = new javax.swing.JButton(); FormListener formListener = new FormListener(); org.jdesktop.swingbinding.JTableBinding jTableBinding = org.jdesktop.swingbinding.SwingBindings.createJTableBinding(org.jdesktop.beansbinding.AutoBinding.UpdateStrategy.READ_WRITE, list, masterTable); org.jdesktop.swingbinding.JTableBinding.ColumnBinding columnBinding = jTableBinding.addColumnBinding(org.jdesktop.beansbinding.ELProperty.create("${id}")); columnBinding.setColumnName("Id"); columnBinding.setColumnClass(Integer.class); columnBinding = jTableBinding.addColumnBinding(org.jdesktop.beansbinding.ELProperty.create("${usernmae}")); columnBinding.setColumnName("Usernmae"); columnBinding.setColumnClass(String.class); columnBinding = jTableBinding.addColumnBinding(org.jdesktop.beansbinding.ELProperty.create("${password}")); columnBinding.setColumnName("Password"); columnBinding.setColumnClass(String.class); columnBinding = jTableBinding.addColumnBinding(org.jdesktop.beansbinding.ELProperty.create("${name}")); columnBinding.setColumnName("Name"); columnBinding.setColumnClass(String.class); bindingGroup.addBinding(jTableBinding); masterScrollPane.setViewportView(masterTable); idLabel.setText("Id:"); usernmaeLabel.setText("Usernmae:"); passwordLabel.setText("Password:"); nameLabel.setText("Name:"); org.jdesktop.beansbinding.Binding binding = org.jdesktop.beansbinding.Bindings.createAutoBinding(org.jdesktop.beansbinding.AutoBinding.UpdateStrategy.READ_WRITE, masterTable, org.jdesktop.beansbinding.ELProperty.create("${selectedElement.id}"), idField, org.jdesktop.beansbinding.BeanProperty.create("text")); binding.setSourceUnreadableValue("null"); bindingGroup.addBinding(binding); binding = org.jdesktop.beansbinding.Bindings.createAutoBinding(org.jdesktop.beansbinding.AutoBinding.UpdateStrategy.READ, masterTable, org.jdesktop.beansbinding.ELProperty.create("${selectedElement != null}"), idField, org.jdesktop.beansbinding.BeanProperty.create("enabled")); bindingGroup.addBinding(binding); binding = org.jdesktop.beansbinding.Bindings.createAutoBinding(org.jdesktop.beansbinding.AutoBinding.UpdateStrategy.READ_WRITE, masterTable, org.jdesktop.beansbinding.ELProperty.create("${selectedElement.usernmae}"), usernmaeField, org.jdesktop.beansbinding.BeanProperty.create("text")); binding.setSourceUnreadableValue("null"); bindingGroup.addBinding(binding); binding = org.jdesktop.beansbinding.Bindings.createAutoBinding(org.jdesktop.beansbinding.AutoBinding.UpdateStrategy.READ, masterTable, org.jdesktop.beansbinding.ELProperty.create("${selectedElement != null}"), usernmaeField, org.jdesktop.beansbinding.BeanProperty.create("enabled")); bindingGroup.addBinding(binding); binding = org.jdesktop.beansbinding.Bindings.createAutoBinding(org.jdesktop.beansbinding.AutoBinding.UpdateStrategy.READ_WRITE, masterTable, org.jdesktop.beansbinding.ELProperty.create("${selectedElement.password}"), passwordField, org.jdesktop.beansbinding.BeanProperty.create("text")); binding.setSourceUnreadableValue("null"); bindingGroup.addBinding(binding); binding = org.jdesktop.beansbinding.Bindings.createAutoBinding(org.jdesktop.beansbinding.AutoBinding.UpdateStrategy.READ, masterTable, org.jdesktop.beansbinding.ELProperty.create("${selectedElement != null}"), passwordField, org.jdesktop.beansbinding.BeanProperty.create("enabled")); bindingGroup.addBinding(binding); binding = org.jdesktop.beansbinding.Bindings.createAutoBinding(org.jdesktop.beansbinding.AutoBinding.UpdateStrategy.READ_WRITE, masterTable, org.jdesktop.beansbinding.ELProperty.create("${selectedElement.name}"), nameField, org.jdesktop.beansbinding.BeanProperty.create("text")); binding.setSourceUnreadableValue("null"); bindingGroup.addBinding(binding); binding = org.jdesktop.beansbinding.Bindings.createAutoBinding(org.jdesktop.beansbinding.AutoBinding.UpdateStrategy.READ, masterTable, org.jdesktop.beansbinding.ELProperty.create("${selectedElement != null}"), nameField, org.jdesktop.beansbinding.BeanProperty.create("enabled")); bindingGroup.addBinding(binding); saveButton.setText("Save"); saveButton.addActionListener(formListener); refreshButton.setText("Refresh"); refreshButton.addActionListener(formListener); newButton.setText("New"); newButton.addActionListener(formListener); deleteButton.setText("Delete"); binding = org.jdesktop.beansbinding.Bindings.createAutoBinding(org.jdesktop.beansbinding.AutoBinding.UpdateStrategy.READ, masterTable, org.jdesktop.beansbinding.ELProperty.create("${selectedElement != null}"), deleteButton, org.jdesktop.beansbinding.BeanProperty.create("enabled")); bindingGroup.addBinding(binding); deleteButton.addActionListener(formListener); javax.swing.GroupLayout layout = new javax.swing.GroupLayout(this); this.setLayout(layout); layout.setHorizontalGroup( layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING) .addGroup(javax.swing.GroupLayout.Alignment.TRAILING, layout.createSequentialGroup() .addComponent(newButton) .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED) .addComponent(deleteButton) .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED) .addComponent(refreshButton) .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED) .addComponent(saveButton) .addContainerGap()) .addGroup(layout.createSequentialGroup() .addContainerGap() .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING) .addComponent(idLabel) .addComponent(usernmaeLabel) .addComponent(passwordLabel) .addComponent(nameLabel)) .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED) .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING) .addComponent(idField, javax.swing.GroupLayout.DEFAULT_SIZE, 315, Short.MAX_VALUE) .addComponent(usernmaeField, javax.swing.GroupLayout.DEFAULT_SIZE, 315, Short.MAX_VALUE) .addComponent(passwordField, javax.swing.GroupLayout.DEFAULT_SIZE, 315, Short.MAX_VALUE) .addComponent(nameField, javax.swing.GroupLayout.DEFAULT_SIZE, 315, Short.MAX_VALUE)) .addContainerGap()) .addGroup(layout.createSequentialGroup() .addContainerGap() .addComponent(masterScrollPane, javax.swing.GroupLayout.DEFAULT_SIZE, 380, Short.MAX_VALUE) .addContainerGap()) ); layout.linkSize(javax.swing.SwingConstants.HORIZONTAL, new java.awt.Component[] {deleteButton, newButton, refreshButton, saveButton}); layout.setVerticalGroup( layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING) .addGroup(layout.createSequentialGroup() .addContainerGap() .addComponent(masterScrollPane, javax.swing.GroupLayout.DEFAULT_SIZE, 130, Short.MAX_VALUE) .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED) .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE) .addComponent(idLabel) .addComponent(idField, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)) .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED) .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE) .addComponent(usernmaeLabel) .addComponent(usernmaeField, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)) .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED) .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE) .addComponent(passwordLabel) .addComponent(passwordField, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)) .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED) .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE) .addComponent(nameLabel) .addComponent(nameField, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)) .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED) .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE) .addComponent(saveButton) .addComponent(refreshButton) .addComponent(deleteButton) .addComponent(newButton)) .addContainerGap()) ); bindingGroup.bind(); } // Code for dispatching events from components to event handlers. private class FormListener implements java.awt.event.ActionListener { FormListener() {} public void actionPerformed(java.awt.event.ActionEvent evt) { if (evt.getSource() == saveButton) { MasterDetailForm.this.saveButtonActionPerformed(evt); } else if (evt.getSource() == refreshButton) { MasterDetailForm.this.refreshButtonActionPerformed(evt); } else if (evt.getSource() == newButton) { MasterDetailForm.this.newButtonActionPerformed(evt); } else if (evt.getSource() == deleteButton) { MasterDetailForm.this.deleteButtonActionPerformed(evt); } } }// </editor-fold> @SuppressWarnings("unchecked") private void refreshButtonActionPerformed(java.awt.event.ActionEvent evt) { entityManager.getTransaction().rollback(); entityManager.getTransaction().begin(); java.util.Collection data = query.getResultList(); for (Object entity : data) { entityManager.refresh(entity); } list.clear(); list.addAll(data); } private void deleteButtonActionPerformed(java.awt.event.ActionEvent evt) { int[] selected = masterTable.getSelectedRows(); List<com.cc.jpa.User> toRemove = new ArrayList<com.cc.jpa.User>(selected.length); for (int idx = 0; idx < selected.length; idx++) { com.cc.jpa.User u = list.get(masterTable.convertRowIndexToModel(selected[idx])); toRemove.add(u); entityManager.remove(u); } list.removeAll(toRemove); } private void newButtonActionPerformed(java.awt.event.ActionEvent evt) { com.cc.jpa.User u = new com.cc.jpa.User(); entityManager.persist(u); list.add(u); int row = list.size() - 1; masterTable.setRowSelectionInterval(row, row); masterTable.scrollRectToVisible(masterTable.getCellRect(row, 0, true)); } private void saveButtonActionPerformed(java.awt.event.ActionEvent evt) { try { entityManager.getTransaction().commit(); entityManager.getTransaction().begin(); } catch (RollbackException rex) { rex.printStackTrace(); entityManager.getTransaction().begin(); List<com.cc.jpa.User> merged = new ArrayList<com.cc.jpa.User>(list.size()); for (com.cc.jpa.User u : list) { merged.add(entityManager.merge(u)); } list.clear(); list.addAll(merged); } } // Variables declaration - do not modify private javax.swing.JButton deleteButton; private javax.persistence.EntityManager entityManager; private javax.swing.JTextField idField; private javax.swing.JLabel idLabel; private java.util.List<com.cc.jpa.User> list; private javax.swing.JScrollPane masterScrollPane; private javax.swing.JTable masterTable; private javax.swing.JTextField nameField; private javax.swing.JLabel nameLabel; private javax.swing.JButton newButton; private javax.swing.JTextField passwordField; private javax.swing.JLabel passwordLabel; private javax.persistence.Query query; private javax.swing.JButton refreshButton; private javax.swing.JButton saveButton; private javax.swing.JTextField usernmaeField; private javax.swing.JLabel usernmaeLabel; private org.jdesktop.beansbinding.BindingGroup bindingGroup; // End of variables declaration public static void main(String[] args) { /* Set the Nimbus look and feel */ //<editor-fold defaultstate="collapsed" desc=" Look and feel setting code (optional) "> /* If Nimbus (introduced in Java SE 6) is not available, stay with the default look and feel. * For details see http://download.oracle.com/javase/tutorial/uiswing/lookandfeel/plaf.html */ try { for (javax.swing.UIManager.LookAndFeelInfo info : javax.swing.UIManager.getInstalledLookAndFeels()) { if ("Nimbus".equals(info.getName())) { javax.swing.UIManager.setLookAndFeel(info.getClassName()); break; } } } catch (ClassNotFoundException ex) { java.util.logging.Logger.getLogger(MasterDetailForm.class.getName()).log(java.util.logging.Level.SEVERE, null, ex); } catch (InstantiationException ex) { java.util.logging.Logger.getLogger(MasterDetailForm.class.getName()).log(java.util.logging.Level.SEVERE, null, ex); } catch (IllegalAccessException ex) { java.util.logging.Logger.getLogger(MasterDetailForm.class.getName()).log(java.util.logging.Level.SEVERE, null, ex); } catch (javax.swing.UnsupportedLookAndFeelException ex) { java.util.logging.Logger.getLogger(MasterDetailForm.class.getName()).log(java.util.logging.Level.SEVERE, null, ex); } //</editor-fold> /* Create and display the form */ EventQueue.invokeLater(new Runnable() { public void run() { JFrame frame = new JFrame(); frame.setContentPane(new MasterDetailForm()); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); frame.pack(); frame.setVisible(true); } }); } }
主要部分:
entityManager初始化，ccPU是在persistence.xml中定义的persistence-unit 的名称， query 和list的 代码 一个是新建一个查询，另一个是查出所有资料。query其实可以用另一种写法，使用entityManager.createNamedQuery("User.findAll");
查看User.java文件会发现，Netbeans 生成的文件里面默认生成了几个Query，也可以根据需要自行添加，集中管理。
entityManager = java.beans.Beans.isDesignTime() ? null : javax.persistence.Persistence.createEntityManagerFactory("ccPU").createEntityManager();
query = java.beans.Beans.isDesignTime() ? null : entityManager.createQuery("SELECT u FROM User u"); list = java.beans.Beans.isDesignTime() ? java.util.Collections.emptyList() : org.jdesktop.observablecollections.ObservableCollections.observableList(query.getResultList());
User:
/* * To change this license header, choose License Headers in Project Properties. * To change this template file, choose Tools | Templates * and open the template in the editor. */ package com.cc.jpa; import java.beans.PropertyChangeListener; import java.beans.PropertyChangeSupport; import java.io.Serializable; import javax.persistence.Basic; import javax.persistence.Column; import javax.persistence.Entity; import javax.persistence.Id; import javax.persistence.NamedQueries; import javax.persistence.NamedQuery; import javax.persistence.Table; import javax.persistence.Transient; /** * * @author dev */ @Entity @Table(name = "user", catalog = "cc", schema = "") @NamedQueries({ @NamedQuery(name = "User.findAll", query = "SELECT u FROM User u"), @NamedQuery(name = "User.findById", query = "SELECT u FROM User u WHERE u.id = :id"), @NamedQuery(name = "User.findByUsernmae", query = "SELECT u FROM User u WHERE u.usernmae = :usernmae"), @NamedQuery(name = "User.findByPassword", query = "SELECT u FROM User u WHERE u.password = :password"), @NamedQuery(name = "User.findByName", query = "SELECT u FROM User u WHERE u.name = :name")}) public class User implements Serializable { @Transient private PropertyChangeSupport changeSupport = new PropertyChangeSupport(this); private static final long serialVersionUID = 1L; @Id @Basic(optional = false) @Column(name = "id") private Integer id; @Basic(optional = false) @Column(name = "usernmae") private String usernmae; @Basic(optional = false) @Column(name = "password") private String password; @Basic(optional = false) @Column(name = "name") private String name; public User() { } public User(Integer id) { this.id = id; } public User(Integer id, String usernmae, String password, String name) { this.id = id; this.usernmae = usernmae; this.password = password; this.name = name; } public Integer getId() { return id; } public void setId(Integer id) { Integer oldId = this.id; this.id = id; changeSupport.firePropertyChange("id", oldId, id); } public String getUsernmae() { return usernmae; } public void setUsernmae(String usernmae) { String oldUsernmae = this.usernmae; this.usernmae = usernmae; changeSupport.firePropertyChange("usernmae", oldUsernmae, usernmae); } public String getPassword() { return password; } public void setPassword(String password) { String oldPassword = this.password; this.password = password; changeSupport.firePropertyChange("password", oldPassword, password); } public String getName() { return name; } public void setName(String name) { String oldName = this.name; this.name = name; changeSupport.firePropertyChange("name", oldName, name); } @Override public int hashCode() { int hash = 0; hash += (id != null ? id.hashCode() : 0); return hash; } @Override public boolean equals(Object object) { // TODO: Warning - this method won't work in the case the id fields are not set if (!(object instanceof User)) { return false; } User other = (User) object; if ((this.id == null && other.id != null) || (this.id != null && !this.id.equals(other.id))) { return false; } return true; } @Override public String toString() { return "com.cc.jpa.User[ id=" + id + " ]"; } public void addPropertyChangeListener(PropertyChangeListener listener) { changeSupport.addPropertyChangeListener(listener); } public void removePropertyChangeListener(PropertyChangeListener listener) { changeSupport.removePropertyChangeListener(listener); } }
New，主要是新增一个新的User对象，没有写到数据库中，主要是前端操作
com.cc.jpa.User u = new com.cc.jpa.User(); entityManager.persist(u); list.add(u); int row = list.size() - 1; masterTable.setRowSelectionInterval(row, row); masterTable.scrollRectToVisible(masterTable.getCellRect(row, 0, true));
Delete，执行entityManager.remove(u)并没有写到数据库是因为有开启Transaction ，在保存的时候才会commit
int[] selected = masterTable.getSelectedRows();
List<com.cc.jpa.User> toRemove = new ArrayList<com.cc.jpa.User>(selected.length); for (int idx = 0; idx < selected.length; idx++) { com.cc.jpa.User u = list.get(masterTable.convertRowIndexToModel(selected[idx])); toRemove.add(u); entityManager.remove(u); } list.removeAll(toRemove);
Save，主要就是Transaction 的提交以及异常处理
try {
entityManager.getTransaction().commit();
entityManager.getTransaction().begin();
} catch (RollbackException rex) {
rex.printStackTrace();
entityManager.getTransaction().begin();
List<com.cc.jpa.User> merged = new ArrayList<com.cc.jpa.User>(list.size());
for (com.cc.jpa.User u : list) {
merged.add(entityManager.merge(u));
}
list.clear();
list.addAll(merged);
}
Refresh，同步数据库数据
entityManager.getTransaction().rollback(); entityManager.getTransaction().begin(); java.util.Collection data = query.getResultList(); for (Object entity : data) { entityManager.refresh(entity); } list.clear(); list.addAll(data);
此范例主要是J2SE 下JPA的使用，实际项目中，可能设计很多table，程式也会相应的分层，如果只是学习一下JPA的特性熟悉下方法，这种方式也是没问题的。使用eclipse 创建JPA时 EclipseLink 需要单独下载，EclipseLink 前身是Oracle TopLink ，以前商业框架 ADF的一部分，用JPA 选择EclipseLink ，Hibernate 或其他实现都没有关系，而且只用JPA的功能，不用实现提供的一些扩展的话，切换使用都是没有问题的，就像JSP页面用不同的容器，Tomcat、Jetty、GlassFish结果是没差别的。
